{"id":4577,"date":"2026-09-19T17:04:29","date_gmt":"2026-09-19T09:04:29","guid":{"rendered":"https:\/\/cnkuangya.com\/?p=4577"},"modified":"2026-09-19T17:04:36","modified_gmt":"2026-09-19T09:04:36","slug":"does-an-spd-protect-against-overvoltage","status":"publish","type":"post","link":"https:\/\/cnkuangya.com\/it\/blog\/does-an-spd-protect-against-overvoltage\/","title":{"rendered":"Un SPD protegge dalle sovratensioni? Differenza tra sovratensioni transitorie e temporanee (TOV)"},"content":{"rendered":"<p class=\"wp-block-paragraph\"><strong>Un SPD protegge dalle sovratensioni?<\/strong> L'espressione.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\"protezione contro le sovratensioni\" <strong>\u201cpu\u00f2 essere fuorviante, poich\u00e9 non ogni sovratensione \u00e8 un impulso transitorio.\u201d<\/strong> Si considerino tre situazioni:.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Consider three situations:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Una sovratensione indotta da fulmine raggiunge un quadro elettrico solo per una frazione di secondo.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La tensione di alimentazione aumenta significativamente per diversi secondi a causa di un guasto di rete.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Oppure un neutro allentato causa il permanere di una tensione anomala su parte dell'impianto finch\u00e9 il guasto non viene riparato.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Tutti e tre comportano <strong>sovratensione<\/strong>, ma non sono lo stesso evento elettrico.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">E un SPD non risponde a tutti loro allo stesso modo.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La distinzione pi\u00f9 importante \u00e8 questa:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>Un SPD convenzionale \u00e8 progettato principalmente per limitare le sovratensioni transitorie. Non dovrebbe essere trattato automaticamente come protezione contro tensioni di alimentazione anomale temporanee o prolungate.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Questa distinzione influenza la scelta dell'SPD, l'analisi dei guasti e persino il modo in cui i tecnici interpretano un SPD danneggiato.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><a href=\"https:\/\/webstore.iec.ch\/en\/publication\/65315\" rel=\"noopener\">IEC 61643-01:2024<\/a> definisce gli SPD a bassa tensione come dispositivi contenenti almeno un componente non lineare e destinati a <strong>limitare le sovratensioni e deviare le correnti di scarica<\/strong>. Per i sistemi di alimentazione a bassa tensione in CA, i requisiti di prodotto sono forniti in <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/65314\" rel=\"noopener\">IEC 61643-11:2025<\/a>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Risposta rapida: un SPD protegge dalle sovratensioni?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>S\u00ec, ma solo da determinati tipi di sovratensione.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Un SPD \u00e8 progettato principalmente per <strong>sovratensioni transitorie<\/strong>, come quelle causate da effetti di fulmini o eventi di commutazione.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Normalmente non \u00e8 inteso per regolare la tensione di alimentazione o scollegare i carichi quando la tensione RMS rimane troppo elevata.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La tabella sottostante mostra la differenza fondamentale.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Condizione elettrica<\/th><th>Caratteristica tipica<\/th><th>Rischio principale<\/th><th>Cosa fa normalmente un SPD<\/th><\/tr><tr><td>Sovratensione transitoria<\/td><td>Impulso brevissimo<\/td><td>Danno all'isolamento\/elettronico<\/td><td>Devia la corrente di sovratensione e limita la tensione<\/td><\/tr><tr><td>Sovratensione temporanea (TOV)<\/td><td>Tensione a frequenza industriale elevata per un periodo temporaneo<\/td><td>Riscaldamento e sovraccarico elettrico<\/td><td>Pu\u00f2 resistervi o raggiungere una condizione definita di guasto\/disconnessione, a seconda dell'SPD<\/td><\/tr><tr><td>Tensione anomala prolungata<\/td><td>L'alimentazione rimane al di fuori del normale intervallo operativo<\/td><td>Surriscaldamento\/danneggiamento continuo delle apparecchiature<\/td><td>Non deve essere considerato come protezione principale<\/td><\/tr><tr><td>Sottotensione<\/td><td>La tensione di alimentazione scende al di sotto dell'intervallo normale<\/td><td>Malfunzionamento del motore\/apparecchiatura<\/td><td>L'SPD convenzionale non corregge il problema<\/td><\/tr><tr><td>Sovracorrente \/ cortocircuito<\/td><td>Carico eccessivo o corrente di guasto<\/td><td>Surriscaldamento del conduttore\/apparecchiatura<\/td><td>Il fusibile o l'interruttore automatico svolgono questa funzione<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/transient-surge-vs-tov-vs-sustained-overvoltage-1024x576.jpg\" alt=\"Transient surge vs TOV vs sustained overvoltage\" class=\"wp-image-4579\" srcset=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/transient-surge-vs-tov-vs-sustained-overvoltage-1024x576.jpg 1024w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/transient-surge-vs-tov-vs-sustained-overvoltage-300x169.jpg 300w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/transient-surge-vs-tov-vs-sustained-overvoltage-768x432.jpg 768w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/transient-surge-vs-tov-vs-sustained-overvoltage-1536x864.jpg 1536w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/transient-surge-vs-tov-vs-sustained-overvoltage-18x10.jpg 18w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/transient-surge-vs-tov-vs-sustained-overvoltage-600x338.jpg 600w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/transient-surge-vs-tov-vs-sustained-overvoltage.jpg 1672w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Un picco transitorio, una sovratensione temporanea e una sovratensione permanente differiscono principalmente per durata, causa e protezione richiesta.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Ecco perch\u00e9 la domanda:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\u201cIl mio quadro ha gi\u00e0 un SPD?\u201d<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">non \u00e8 la stessa cosa di:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\u201cLa mia apparecchiatura \u00e8 protetta contro ogni condizione di tensione anomala?\u201d<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Non lo \u00e8.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Picco transitorio vs TOV vs Sovratensione permanente<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Il termine <strong>sovratensione<\/strong> \u00e8 una categoria ampia.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Comprendere la durata e la causa dell'evento \u00e8 essenziale prima di decidere quale dispositivo di protezione debba intervenire.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">1. Sovratensione transitoria<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Una sovratensione transitoria \u00e8 un disturbo di tensione di breve durata.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Le cause tipiche includono:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>effetti dei fulmini;<\/li>\n\n\n\n<li>operazioni di manovra;<\/li>\n\n\n\n<li>commutazione di carichi induttivi;<\/li>\n\n\n\n<li>commutazione di condensatori;<\/li>\n\n\n\n<li>altri eventi transitori nel sistema elettrico.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">I test standard per gli SPD utilizzano comunemente forme d'onda a impulso come <strong>forma d'onda di corrente 8\/20 \u03bcs<\/strong> per applicazioni di Tipo 2.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">L'evento si verifica estremamente rapidamente.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Questo \u00e8 esattamente l'ambiente per cui \u00e8 progettato un SPD. Se desideri esaminare pi\u00f9 in dettaglio il processo di clamping e di deviazione della corrente, consulta la nostra guida su <a href=\"https:\/\/cnkuangya.com\/it\/blog\/how-a-dc-surge-protective-device-spd-works-an-engineers-guide\/\">come funziona un dispositivo di protezione contro le sovratensioni in corrente continua (DC)<\/a>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">2. Sovratensione Temporanea \u2014 TOV<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Una TOV \u00e8 diversa.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La tensione rimane elevata molto pi\u00f9 a lungo di un impulso ed \u00e8 generalmente associata al sistema di alimentazione piuttosto che a un singolo picco su scala di microsecondi.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Le possibili cause possono includere:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>guasti a terra;<\/li>\n\n\n\n<li>problemi al neutro;<\/li>\n\n\n\n<li>condizioni di messa a terra del sistema;<\/li>\n\n\n\n<li>ferro-risonanza;<\/li>\n\n\n\n<li>problemi di regolazione della tensione;<\/li>\n\n\n\n<li>condizioni di commutazione anomale.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">L'intensit\u00e0 da sola non definisce il rischio.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Tensione + durata + modalit\u00e0 di protezione + sistema di messa a terra + design dell'SPD<\/strong> sono tutti fattori rilevanti.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">ABB, ad esempio, distingue <strong>Uc<\/strong>, la massima tensione continuativa di esercizio, da <strong>UT<\/strong>, la tenuta alle sovratensioni temporanee. La sua <a href=\"https:\/\/library.e.abb.com\/public\/5f77fa22e4d3438cad7d4687077bc99c\/1TXH000309C0201_OVR%20practical%20guide.pdf\" rel=\"noopener\">guida pratica OVR<\/a> tratta il comportamento TOV separatamente dalle prestazioni contro le correnti di sovratensione e dimostra che lo stress applicabile dipende dal collegamento dell'SPD e dalla configurazione della rete.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">3. Sovratensione sostenuta o permanente<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Se una tensione di alimentazione anomala persiste invece di comportarsi come un evento di guasto temporaneo, il problema ingegneristico cambia nuovamente.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Un SPD convenzionale collegato in parallelo non deve essere utilizzato come regolatore di tensione.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Un dispositivo progettato per monitorare la tensione RMS e avviare la disconnessione \u00e8 normalmente richiesto quando l'obiettivo progettuale \u00e8:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>Scollegare il carico se la tensione di alimentazione rimane al di sopra o al di sotto di una soglia accettabile.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Ad esempio, Schneider Electric <a href=\"https:\/\/www.se.com\/us\/en\/product\/RM22TR33\/3phase-control-relay-harmony-control-relays-8a-2co-380-480v-ac\/\" rel=\"noopener\">Rel\u00e8 di controllo tensione Harmony<\/a> forniscono funzioni di monitoraggio di sovratensione e sottotensione. Questa \u00e8 una funzione diversa dal ruolo di deviazione rapida delle sovratensioni di un SPD.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Perch\u00e9 un SPD pu\u00f2 gestire una sovratensione ma essere danneggiato da una TOV?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This seems contradictory at first.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">An SPD may discharge a very large surge current measured in kiloamperes.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This is why asking <strong>\u201cdoes an SPD protect against overvoltage?\u201d<\/strong> requires first identifying whether the event is a transient surge, a TOV, or a sustained abnormal supply condition.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">So why could a much smaller abnormal AC voltage damage it?<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La risposta \u00e8:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>Energy is not determined by current magnitude alone. Time matters.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Consider an MOV-based SPD.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Under normal operating voltage, the MOV remains in a high-impedance state and conducts only a very small current.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">When a transient surge raises the voltage sufficiently, the MOV becomes conductive.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Surge current is diverted through the SPD and the voltage is limited.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The surge then disappears very quickly.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The MOV returns toward its normal high-impedance state.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A simplified sequence looks like this:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Palcoscenico<\/th><th>Voltage condition<\/th><th>MOV behavior<\/th><\/tr><tr><td>Normal operation<\/td><td>Below its conduction region<\/td><td>High impedance<\/td><\/tr><tr><td>Surge arrives<\/td><td>Voltage rises rapidly<\/td><td>MOV becomes conductive<\/td><\/tr><tr><td>Surge current flows<\/td><td>Very short high-energy event<\/td><td>Energy is absorbed\/diverted<\/td><\/tr><tr><td>Surge ends<\/td><td>Voltage returns to normal<\/td><td>MOV returns toward standby<\/td><\/tr><tr><td>TOV persists<\/td><td>Voltage remains abnormally high<\/td><td>Continued conduction may produce heat<\/td><\/tr><tr><td>Excessive thermal stress<\/td><td>Temperature continues increasing<\/td><td>Thermal disconnector may operate or MOV may be damaged<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/mov-behavior-during-surge-and-tov-1024x576.jpg\" alt=\"MOV behavior during transient surge and TOV\" class=\"wp-image-4580\" srcset=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/mov-behavior-during-surge-and-tov-1024x576.jpg 1024w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/mov-behavior-during-surge-and-tov-300x169.jpg 300w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/mov-behavior-during-surge-and-tov-768x432.jpg 768w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/mov-behavior-during-surge-and-tov-1536x864.jpg 1536w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/mov-behavior-during-surge-and-tov-18x10.jpg 18w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/mov-behavior-during-surge-and-tov-600x338.jpg 600w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/mov-behavior-during-surge-and-tov.jpg 1672w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">An MOV can conduct briefly during a surge, while prolonged abnormal voltage may create continuous heating and thermal stress.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">That last condition is the problem.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">If the voltage does not disappear quickly enough, the MOV may continue conducting.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Electrical energy then becomes heat.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In simplified form:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>abnormal voltage \u2192 MOV current \u2192 power dissipation \u2192 temperature rise \u2192 disconnector operation or component damage<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This is why:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>40 kA Imax does not mean that an SPD can withstand any abnormal supply voltage.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Imax describes a defined <strong>surge-current capability<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">TOV behavior describes a completely different type of electrical stress.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Uc, Up and TOV: Three Different Questions<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Another common source of confusion is mixing voltage specifications together.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Suppose an SPD datasheet contains <strong>Uc<\/strong>, <strong>Su<\/strong> and a TOV\/UT specification.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">They should not be compared as though they describe the same thing.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Parametro<\/th><th>Main question it answers<\/th><th>What it does NOT tell you<\/th><\/tr><tr><td><strong>Uc \/ MCOV<\/strong><\/td><td>What voltage can remain continuously across the SPD under specified conditions?<\/td><td>Surge protection level<\/td><\/tr><tr><td><strong>Su<\/strong><\/td><td>How much voltage appears at the SPD during standardized surge testing?<\/td><td>Maximum continuous voltage<\/td><\/tr><tr><td><strong>UT \/ TOV behavior<\/strong><\/td><td>How does the SPD behave during a specified temporary abnormal voltage condition?<\/td><td>Universal protection against every overvoltage<\/td><\/tr><tr><td><strong>In<\/strong><\/td><td>What nominal surge current is used for the relevant discharge-current test?<\/td><td>TOV withstand<\/td><\/tr><tr><td><strong>Imax<\/strong><\/td><td>What maximum discharge current is declared for the relevant Type 2 test?<\/td><td>Ability to survive neutral loss<\/td><\/tr><tr><td><strong>Iimp<\/strong><\/td><td>What impulse-current duty is declared for Type 1 applications?<\/td><td>Sustained-overvoltage protection<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-uc-up-tov-rating-explained-1024x576.jpg\" alt=\"SPD Uc Up and TOV ratings explained\" class=\"wp-image-4581\" srcset=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-uc-up-tov-rating-explained-1024x576.jpg 1024w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-uc-up-tov-rating-explained-300x169.jpg 300w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-uc-up-tov-rating-explained-768x432.jpg 768w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-uc-up-tov-rating-explained-1536x864.jpg 1536w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-uc-up-tov-rating-explained-18x10.jpg 18w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-uc-up-tov-rating-explained-600x338.jpg 600w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-uc-up-tov-rating-explained.jpg 1672w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Uc, Up and TOV behavior describe different aspects of SPD performance and should not be treated as interchangeable ratings.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The IEC definition of an SPD focuses on limiting <strong>surge voltage<\/strong> and diverting <strong>surge current<\/strong>. <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/32531\" rel=\"noopener\">IEC 61643-12:2020<\/a> separately covers selection, operation, location and coordination principles for AC power SPDs. If the differences between <strong>Uc, Up, In, Imax and Iscpv<\/strong> are not yet clear, see our <a href=\"https:\/\/cnkuangya.com\/it\/blog\/dc-spd-specifications\/\">guida alle specifiche degli SPD in corrente continua<\/a>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Does Higher Uc Mean Better TOV Protection?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Not automatically.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It is tempting to think:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">Higher Uc = safer SPD.<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">\u00c8 troppo semplicistico.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A suitably higher Uc can give more operating-voltage margin, but SPD selection involves a tradeoff.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The device must remain stable at the expected continuous system voltage while still providing an appropriate surge protection level.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">NIST researchers have described this design dilemma for decades: an SPD must provide effective surge limitation without being expected to clamp longer-duration power-frequency overvoltages indefinitely.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Pertanto:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>Do not deliberately oversize Uc simply because you are worried about TOV.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Instead, check:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Domanda<\/th><th>Perch\u00e9 \u00e8 importante<\/th><\/tr><tr><td>What is the nominal system voltage?<\/td><td>Establishes basic operating condition<\/td><\/tr><tr><td>What is the maximum expected continuous voltage?<\/td><td>Determines Uc compatibility<\/td><\/tr><tr><td>What is the earthing system?<\/td><td>Influences voltage appearing across protection modes<\/td><\/tr><tr><td>Which protection modes are used?<\/td><td>L-N and L-PE may see different stresses<\/td><\/tr><tr><td>What TOV behavior does the manufacturer declare?<\/td><td>Determines behavior under specified fault conditions<\/td><\/tr><tr><td>What Up is required?<\/td><td>Determines surge-voltage limitation<\/td><\/tr><tr><td>What does the protected equipment tolerate?<\/td><td>Required for insulation coordination<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Real Case 1: A Documented TOV Above 150% Lasted About Four Seconds<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This is where the distinction stops being theoretical.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A <a href=\"https:\/\/www.nist.gov\/publications\/dilemma-surge-protection-vs-overvoltage-scenarios-implications-low-voltage-surge\" rel=\"noopener\">NIST-hosted paper by Fran\u00e7ois Martzloff and Arshad Mansoor<\/a> discusses actual power-system overvoltage scenarios.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">One example cited from an EPRI report involved a power-system switching incident during restoration of power phase by phase.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The recorded condition produced an RMS voltage exceeding <strong>150% of normal voltage for approximately four seconds<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The researchers identified the phenomenon as a temporary overvoltage associated with ferroresonance.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Notice what makes this different from a normal SPD surge event:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Lightning\/switching impulse<\/th><th>Documented TOV case<\/th><\/tr><tr><td>Extremely short<\/td><td>About 4 seconds<\/td><\/tr><tr><td>Typically discussed with impulse waveforms<\/td><td>Power-frequency RMS voltage remained elevated<\/td><\/tr><tr><td>SPD diverts impulse energy<\/td><td>SPD may remain electrically stressed for much longer<\/td><\/tr><tr><td>Surge current rating is important<\/td><td>TOV behavior and continuous-voltage margin become critical<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Four seconds may sound short to a person.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For an MOV that is dissipating abnormal power continuously, it is extremely long compared with a microsecond-scale surge.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Real Case 2: Commercial SPDs Were Tested Under Simulated TOV Conditions<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Another <a href=\"https:\/\/www.nist.gov\/system\/files\/documents\/pml\/div684\/TOVs_on_SPDs.pdf\" rel=\"noopener\">NIST-hosted TOV study<\/a> by researchers from Eaton Electrical, EPRI Solutions and Fran\u00e7ois Martzloff investigated what happens when commercial SPDs experience several TOV conditions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The study intentionally exposed commercial devices to conditions representing real power-system abnormalities.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The test program included the following examples:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Simulated condition<\/th><th>Applied stress<\/th><\/tr><tr><td>Poor voltage regulation<\/td><td>1.15 pu \/ 138 V for 6 hours<\/td><\/tr><tr><td>Power-system fault<\/td><td>1.3 pu \/ 156 V for 2 seconds<\/td><\/tr><tr><td>Loss of secondary neutral<\/td><td>1.5 pu \/ 180 V for 4 hours<\/td><\/tr><tr><td>Ferroresonance<\/td><td>2.0 pu \/ 240 V for 1 minute<\/td><\/tr><tr><td>High-voltage conductor contact with LV system<\/td><td>3.0 pu \/ 360 V for 1 second<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The values relate to the study&#8217;s 120 V system basis; they must <strong>non<\/strong> be copied directly as ratings for another SPD or another electrical system.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The result was especially important.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The researchers found that SPD response varied substantially depending on the product design.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The three cord-connected SPD specimens failed under the simulated 1.5 pu neutral-loss condition, while the two permanently connected specimens used in that study survived the first four test scenarios. Under the extreme 3.0 pu test, the permanently connected specimens experienced partial internal failure but retained some protective capability.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This should <strong>non<\/strong> be interpreted as:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\u201cHardwired SPDs always survive TOV.\u201d<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">The study used only a small group of specific products and represents historical designs.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Its real lesson is more useful:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>Two products with similar-looking surge ratings may behave very differently under a long-duration abnormal voltage condition.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">That is why TOV cannot be judged from Imax alone.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-tov-laboratory-test-example-1024x576.jpg\" alt=\"SPD temporary overvoltage laboratory test example\" class=\"wp-image-4582\" srcset=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-tov-laboratory-test-example-1024x576.jpg 1024w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-tov-laboratory-test-example-300x169.jpg 300w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-tov-laboratory-test-example-768x432.jpg 768w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-tov-laboratory-test-example-1536x864.jpg 1536w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-tov-laboratory-test-example-18x10.jpg 18w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-tov-laboratory-test-example-600x338.jpg 600w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-tov-laboratory-test-example.jpg 1672w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Laboratory TOV testing exposes SPDs to abnormal power-frequency voltage for much longer than a conventional surge impulse.<\/figcaption><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Does an SPD Protect Against Overvoltage Caused by Neutral Loss?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Neutral interruption is one of the most useful examples because it explains why the phrase <strong>\u201cthe SPD should clamp the voltage\u201d<\/strong> can become dangerous.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In a multi-wire system with unequal phase-to-neutral loads, loss of the neutral can shift the neutral point.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The voltage across individual loads can then become severely unbalanced.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">NIST describes loss-of-neutral conditions in North American 120\/240 V three-wire systems where one side can approach twice normal voltage depending on the connected load impedances. The paper notes that such neutral problems may result from loose connections, mechanical damage or corrosion.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Now imagine an MOV-based SPD connected across the affected conductors.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">If the abnormal power-frequency voltage pushes the MOV into conduction:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>it begins conducting continuously.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">But an MOV is not supposed to behave like a voltage regulator carrying that current indefinitely.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It may heat rapidly.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Eventually the result may be:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Possible outcome<\/th><th>What it means<\/th><\/tr><tr><td>SPD withstands the event<\/td><td>Device remains functional within its declared condition<\/td><\/tr><tr><td>Internal thermal disconnector operates<\/td><td>Surge protection on that mode may be lost<\/td><\/tr><tr><td>Backup protection operates<\/td><td>SPD branch may be disconnected<\/td><\/tr><tr><td>MOV suffers damage<\/td><td>Module may require replacement<\/td><\/tr><tr><td>Status indicator changes<\/td><td>Maintenance is required<\/td><\/tr><tr><td>Load remains energized<\/td><td>Equipment may still be exposed to abnormal supply voltage<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The last point is particularly important.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A typical parallel-connected SPD can disconnect <strong>itself<\/strong> while the protected circuit remains energized.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Pertanto:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>SPD failure or disconnection does not necessarily remove the abnormal voltage from the load.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">A conventional SPD should therefore not be relied on as the sole protection against neutral-loss overvoltage. Where the design requires abnormal RMS voltage to be detected and the load disconnected, a dedicated voltage-monitoring or protection function may be needed. The neutral fault itself must still be located and corrected.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Why Doesn&#8217;t the SPD Simply Clamp the TOV?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Because doing so could require the SPD to absorb or divert power continuously.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Consider a simplified example.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A Type 2 MOV-based SPD is installed across the supply.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A brief transient occurs.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The MOV conducts for a very short time and then stops.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">That is normal.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Now assume abnormal mains voltage remains high for many seconds.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">If the MOV attempts to hold the voltage down continuously, the SPD essentially becomes part of a power-frequency current path.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The longer the current flows, the greater the thermal stress.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">That can lead to:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>thermal runaway \u2192 disconnector operation \u2192 loss of SPD protection or component damage<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This is exactly why SPDs require coordinated fault and disconnection behavior rather than simply \u201cclamping everything.\u201d<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">TOV Withstand Does Not Mean TOV Protection for the Load<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This distinction is extremely important when reading datasheets.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Suppose a manufacturer states that an SPD has a certain <strong>UT<\/strong> or TOV capability.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">That generally describes the SPD&#8217;s behavior under specified test conditions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It does <strong>not automatically mean<\/strong>:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\u201cThe downstream equipment will remain at normal voltage throughout the TOV.\u201d<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">These are different functions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Compare them:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Funzione<\/th><th>SPD<\/th><th>Voltage monitoring \/ overvoltage protection<\/th><\/tr><tr><td>Detect fast transient surge<\/td><td>S\u00ec<\/td><td>Usually not its primary purpose<\/td><\/tr><tr><td>Divert surge current<\/td><td>S\u00ec<\/td><td>No<\/td><\/tr><tr><td>Limit impulse voltage<\/td><td>S\u00ec<\/td><td>No<\/td><\/tr><tr><td>Continuously monitor RMS voltage<\/td><td>Not normally its main function<\/td><td>S\u00ec<\/td><\/tr><tr><td>Adjustable OV\/UV thresholds<\/td><td>Normally no<\/td><td>Often yes<\/td><\/tr><tr><td>Time-delay operation<\/td><td>Not in the same sense<\/td><td>Comune<\/td><\/tr><tr><td>Disconnect load during persistent abnormal voltage<\/td><td>Solitamente no<\/td><td>Can command or perform disconnection, depending on system design<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Schneider&#8217;s Harmony control relays, for example, monitor overvoltage and undervoltage conditions with threshold and timing functions; this is fundamentally different from the shunt surge-diversion function of an SPD.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Can a Circuit Breaker Protect Against Overvoltage?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A standard circuit breaker should not automatically be treated as an overvoltage protector either.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Its primary job is overcurrent protection.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">If voltage rises while load current remains below the breaker trip characteristic, an ordinary breaker may remain closed.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">That means four devices can perform four different functions:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Dispositivo<\/th><th>Primary protection function<\/th><\/tr><tr><td>SPD<\/td><td>Sovratensione transitoria<\/td><\/tr><tr><td>Fusibile<\/td><td>Overcurrent \/ short-circuit protection<\/td><\/tr><tr><td>Interruttore automatico<\/td><td>Overcurrent \/ short-circuit protection<\/td><\/tr><tr><td>Voltage monitoring relay \/ dedicated OV protection<\/td><td>Abnormal supply voltage monitoring and disconnection logic<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">This is why replacing one device with another based only on the word <strong>\u201cprotection\u201d<\/strong> is a mistake. For the separate question of SPD overcurrent coordination, see our guide to <a href=\"https:\/\/cnkuangya.com\/it\/blog\/spd-backup-fuse\/\">SPD backup fuse and circuit-breaker selection<\/a>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Can a Bigger kA SPD Solve a TOV Problem?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">No.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Suppose one SPD is rated:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>In = 20 kA<\/strong><br><strong>Imax = 40 kA<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">and another says:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Imax = 60 kA<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The 60 kA product is not automatically better at surviving a temporary power-frequency overvoltage.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The ratings describe different stresses.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Parametro<\/th><th>Mainly associated with<\/th><\/tr><tr><td>In<\/td><td>Nominal surge discharge duty<\/td><\/tr><tr><td>Imax<\/td><td>Maximum Type 2 discharge-current duty<\/td><\/tr><tr><td>Iimp<\/td><td>Type 1 impulse-current duty<\/td><\/tr><tr><td>Uc<\/td><td>Continuous operating voltage<\/td><\/tr><tr><td>UT \/ TOV<\/td><td>Temporary abnormal-voltage behavior<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Therefore, if SPDs repeatedly fail without obvious lightning activity, simply purchasing a higher-Imax model may not solve the actual problem.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Repeated SPD Failure: What Should You Investigate?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This is a situation where field diagnosis matters more than changing brands.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Use this investigation table.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Osservazione<\/th><th>Check first<\/th><th>Possible explanation<\/th><\/tr><tr><td>New SPD quickly turns red<\/td><td>Actual system voltage<\/td><td>Wrong Uc or abnormal supply<\/td><\/tr><tr><td>Several modules fail repeatedly<\/td><td>Neutral and earthing condition<\/td><td>System fault rather than repeated lightning<\/td><\/tr><tr><td>SPD becomes hot<\/td><td>Continuous voltage across SPD<\/td><td>MOV may be conducting abnormally<\/td><\/tr><tr><td>SPD fails after generator operation<\/td><td>Generator voltage\/frequency regulation<\/td><td>Abnormal supply condition<\/td><\/tr><tr><td>One phase repeatedly damages an SPD<\/td><td>Phase-to-neutral voltage<\/td><td>Neutral displacement or phase-specific fault<\/td><\/tr><tr><td>SPD survives but equipment fails<\/td><td>Event type and protection coordination<\/td><td>Disturbance may not be a transient the SPD can solve<\/td><\/tr><tr><td>Breaker\/fuse trips together with SPD failure<\/td><td>Fault current and backup protection<\/td><td>SPD component may have reached a fault state<\/td><\/tr><tr><td>No lightning was recorded<\/td><td>Do not rule out electrical abnormality<\/td><td>TOV, switching, neutral problems or misapplication are possible<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">NIST&#8217;s historical analysis lists power-system faults, poor voltage regulation, conductor problems, generator conditions, ferroresonance and loss of neutral among conditions capable of contributing to SPD overvoltage stress. If a device already shows a red indicator, abnormal heating or visible damage, our guide on <a href=\"https:\/\/cnkuangya.com\/it\/blog\/how-to-know-if-an-spd-is-bad\/\">come capire se un SPD \u00e8 guasto<\/a> explains the next inspection steps.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-overvoltage-caused-by-neutral-loss-1024x576.jpg\" alt=\"SPD overvoltage caused by neutral loss\" class=\"wp-image-4583\" srcset=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-overvoltage-caused-by-neutral-loss-1024x576.jpg 1024w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-overvoltage-caused-by-neutral-loss-300x169.jpg 300w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-overvoltage-caused-by-neutral-loss-768x432.jpg 768w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-overvoltage-caused-by-neutral-loss-1536x864.jpg 1536w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-overvoltage-caused-by-neutral-loss-18x10.jpg 18w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-overvoltage-caused-by-neutral-loss-600x338.jpg 600w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-overvoltage-caused-by-neutral-loss.jpg 1672w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">A lost or loose neutral can cause abnormal phase-to-neutral voltage, while a conventional SPD should not be used as the primary solution to the neutral fault.<\/figcaption><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">What About TOV in Solar PV DC Systems?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Extra care is required here.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Most discussion of <strong>power-frequency TOV<\/strong> relates to AC systems.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A PV DC system has different operating conditions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Important PV DC concerns include:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>PV consideration<\/th><th>Perch\u00e9 \u00e8 importante<\/th><\/tr><tr><td>Maximum string Voc<\/td><td>Determines maximum DC voltage<\/td><\/tr><tr><td>Low-temperature Voc increase<\/td><td>Can raise actual open-circuit voltage<\/td><\/tr><tr><td>Ucpv<\/td><td>Must match the PV application<\/td><\/tr><tr><td>PV earthing configuration<\/td><td>Changes voltage relationships to earth<\/td><\/tr><tr><td>Inverter topology<\/td><td>Influences system behavior<\/td><\/tr><tr><td>Insulation faults<\/td><td>Can change conductor-to-earth voltage<\/td><\/tr><tr><td>Correct PV SPD standard<\/td><td>AC SPD assumptions cannot simply be transferred<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><a href=\"https:\/\/webstore.iec.ch\/en\/publication\/26931\" rel=\"noopener\">IEC 61643-31:2018<\/a> specifically covers SPDs intended for the DC side of PV installations up to <strong>1500 V CC<\/strong>. <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/27917\" rel=\"noopener\">IEC 61643-41:2025<\/a> now covers general DC low-voltage SPDs up to 1500 V DC, but it explicitly excludes PV applications, which remain within IEC 61643-31.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Therefore, do not take an AC TOV number from a 230\/400 V AC SPD datasheet and assume the same rule applies to a 1000 V or 1500 V PV SPD.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For PV systems, check the exact:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Ucpv + topology + protection mode + manufacturer documentation + applicable PV SPD standard.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For voltage selection, see our <a href=\"https:\/\/cnkuangya.com\/it\/blog\/dc-spd-selection-guide\/\">DC SPD voltage selection guide<\/a>. For grounded versus floating PV arrangements and protection paths, see <a href=\"https:\/\/cnkuangya.com\/it\/blog\/2p-vs-3p-dc-spd\/\">2P vs 3P DC SPD for Solar PV<\/a>.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/pv-dc-spd-overvoltage-protection-1024x576.jpg\" alt=\"PV DC SPD overvoltage protection and Ucpv selection\" class=\"wp-image-4584\" srcset=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/pv-dc-spd-overvoltage-protection-1024x576.jpg 1024w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/pv-dc-spd-overvoltage-protection-300x169.jpg 300w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/pv-dc-spd-overvoltage-protection-768x432.jpg 768w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/pv-dc-spd-overvoltage-protection-1536x864.jpg 1536w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/pv-dc-spd-overvoltage-protection-18x10.jpg 18w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/pv-dc-spd-overvoltage-protection-600x338.jpg 600w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/pv-dc-spd-overvoltage-protection.jpg 1672w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">PV DC SPD selection should consider maximum string voltage, low-temperature Voc, Ucpv, system topology and the applicable PV SPD standard.<\/figcaption><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">AC SPD vs PV DC SPD Under Overvoltage<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This is another reason AC and DC SPDs should not be interchanged casually.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Domanda<\/th><th>SPD CA<\/th><th>PV SPD DC<\/th><\/tr><tr><td>Main supply<\/td><td>AC power system<\/td><td>PV DC circuit<\/td><\/tr><tr><td>Main continuous-voltage rating<\/td><td>Uc<\/td><td>Ucpv<\/td><\/tr><tr><td>Relevant product standard<\/td><td>IEC 61643-11<\/td><td>IEC 61643-31<\/td><\/tr><tr><td>Natural current zero crossing<\/td><td>Present each AC half-cycle<\/td><td>No equivalent periodic zero crossing<\/td><\/tr><tr><td>System topology considerations<\/td><td>TN\/TT\/IT etc.<\/td><td>Grounded\/floating PV topology etc.<\/td><\/tr><tr><td>Can ratings be transferred directly?<\/td><td>-<\/td><td><strong>No<\/strong><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">IEC currently lists IEC 61643-11:2025 for AC low-voltage SPDs, while IEC 61643-31:2018 addresses PV DC SPDs. For a practical explanation of why an AC-only SPD should not simply be moved to a DC circuit, see <a href=\"https:\/\/cnkuangya.com\/it\/blog\/ac-spd-on-dc-system\/\">What Happens If You Use an AC SPD on a DC System?<\/a>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Common Mistakes About SPD and Overvoltage<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Errore<\/th><th>Why it is wrong<\/th><\/tr><tr><td>\u201cAny overvoltage is a surge.\u201d<\/td><td>Event duration and origin matter<\/td><\/tr><tr><td>\u201c40 kA means it can handle stronger mains voltage.\u201d<\/td><td>kA surge rating is not TOV withstand<\/td><\/tr><tr><td>\u201cA lower Up means better TOV performance.\u201d<\/td><td>Up and TOV are different characteristics<\/td><\/tr><tr><td>\u201cIf the SPD disconnects, the load is safe.\u201d<\/td><td>Parallel SPD disconnection may leave the load energized<\/td><\/tr><tr><td>\u201cA bigger SPD fixes neutral loss.\u201d<\/td><td>Neutral fault must be corrected<\/td><\/tr><tr><td>\u201cThe breaker will always trip on overvoltage.\u201d<\/td><td>Standard breakers respond primarily to current<\/td><\/tr><tr><td>\u201cHigher Uc is always better.\u201d<\/td><td>Uc must be coordinated with system voltage and protection objectives<\/td><\/tr><tr><td>\u201cAC and DC overvoltage behavior is the same.\u201d<\/td><td>Circuit behavior and product standards differ<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">How to Select an SPD When TOV Is a Concern<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Instead of starting with:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\u201cHow many kA do I need?\u201d<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">start with the electrical system.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Selection step<\/th><th>What to confirm<\/th><\/tr><tr><td>1<\/td><td>AC or DC application<\/td><\/tr><tr><td>2<\/td><td>Tensione nominale del sistema<\/td><\/tr><tr><td>3<\/td><td>Tensione massima di funzionamento continuo<\/td><\/tr><tr><td>4<\/td><td>Earthing \/ grounding arrangement<\/td><\/tr><tr><td>5<\/td><td>Protection modes<\/td><\/tr><tr><td>6<\/td><td>Uc or Ucpv<\/td><\/tr><tr><td>7<\/td><td>Manufacturer-declared TOV behavior where applicable<\/td><\/tr><tr><td>8<\/td><td>Su<\/td><\/tr><tr><td>9<\/td><td>Tipo SPD<\/td><\/tr><tr><td>10<\/td><td>In \/ Imax \/ Iimp<\/td><\/tr><tr><td>11<\/td><td>Prospective short-circuit conditions<\/td><\/tr><tr><td>12<\/td><td>Backup fuse or breaker requirements<\/td><\/tr><tr><td>13<\/td><td>Installation conductor length<\/td><\/tr><tr><td>14<\/td><td>Status indication \/ remote signaling requirements<\/td><\/tr><tr><td>15<\/td><td>Exact applicable product standard and documentation<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Installation also matters after the product is selected. Long SPD connecting conductors can increase the voltage appearing at the protected equipment during a fast surge; see our guide to <a href=\"https:\/\/cnkuangya.com\/it\/blog\/spd-distance-from-inverter\/\">SPD distance from the inverter and SPD lead length<\/a>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This order avoids a common purchasing mistake:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">choosing the largest kA number first and checking voltage compatibility later.<\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Practical Example: Diagnosing an SPD That Keeps Failing<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Assume an electrician installs a new Type 2 SPD.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A few days later the status window indicates replacement.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A new cartridge is installed.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It fails again.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It would be easy to conclude:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\u201cThe SPD quality is poor.\u201d<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">But that is only one possibility.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A better troubleshooting sequence is:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Controllo<\/th><th>Reason<\/th><\/tr><tr><td>Measure actual supply voltage<\/td><td>Identify sustained abnormal voltage<\/td><\/tr><tr><td>Confirm nominal system voltage<\/td><td>Ensure the correct SPD was selected<\/td><\/tr><tr><td>Verify Uc<\/td><td>Detect voltage-rating mismatch<\/td><\/tr><tr><td>Controllare la continuit\u00e0 del neutro<\/td><td>Find neutral displacement risk<\/td><\/tr><tr><td>Confirm earthing configuration<\/td><td>Ensure correct SPD arrangement<\/td><\/tr><tr><td>Inspect wiring<\/td><td>Exclude installation errors<\/td><\/tr><tr><td>Check backup protection<\/td><td>Verify fault coordination<\/td><\/tr><tr><td>Review event history<\/td><td>Distinguish lightning\/switching from TOV<\/td><\/tr><tr><td>Check other phases<\/td><td>Identify unbalanced voltage<\/td><\/tr><tr><td>Review manufacturer TOV data<\/td><td>Determine whether the event exceeded design conditions<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Only after these checks should repeated SPD replacement be treated as a simple product issue.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">SPD vs Overvoltage Relay: Do You Need Both?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">In some installations, yes.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">They solve different problems.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Think of them this way:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>SPD:<\/strong><br>\u201cWhat happens if a very fast surge arrives?\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Voltage monitoring protection:<\/strong><br>\u201cWhat happens if the supply voltage remains abnormal?\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A system containing both functions may therefore provide broader protection than either one alone.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">But the exact protection design depends on the installation, applicable codes and equipment requirements.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-vs-overvoltage-relay-1024x576.jpg\" alt=\"SPD vs overvoltage relay protection functions\" class=\"wp-image-4585\" srcset=\"https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-vs-overvoltage-relay-1024x576.jpg 1024w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-vs-overvoltage-relay-300x169.jpg 300w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-vs-overvoltage-relay-768x432.jpg 768w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-vs-overvoltage-relay-1536x864.jpg 1536w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-vs-overvoltage-relay-18x10.jpg 18w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-vs-overvoltage-relay-600x338.jpg 600w, https:\/\/cnkuangya.com\/wp-content\/uploads\/2026\/09\/spd-vs-overvoltage-relay.jpg 1672w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">An SPD limits fast transient surges, while voltage-monitoring protection can respond when the supply voltage remains outside an acceptable range.<\/figcaption><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">SPD Overvoltage Protection Checklist<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Before approving an SPD specification, confirm the following:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Controllo<\/th><th>S\u00ec \/ No<\/th><\/tr><tr><td>Is the SPD intended for AC or PV DC?<\/td><td>\u25a1<\/td><\/tr><tr><td>Does Uc\/Ucpv suit the actual maximum operating voltage?<\/td><td>\u25a1<\/td><\/tr><tr><td>Is the system earthing configuration known?<\/td><td>\u25a1<\/td><\/tr><tr><td>Are the required protection modes identified?<\/td><td>\u25a1<\/td><\/tr><tr><td>Has the TOV behavior been checked where relevant?<\/td><td>\u25a1<\/td><\/tr><tr><td>Is Up suitable for the protection concept?<\/td><td>\u25a1<\/td><\/tr><tr><td>Are In\/Imax\/Iimp understood correctly?<\/td><td>\u25a1<\/td><\/tr><tr><td>Is backup protection coordinated?<\/td><td>\u25a1<\/td><\/tr><tr><td>Are short-circuit conditions known?<\/td><td>\u25a1<\/td><\/tr><tr><td>Is the installation wiring short and direct?<\/td><td>\u25a1<\/td><\/tr><tr><td>Is neutral integrity verified?<\/td><td>\u25a1<\/td><\/tr><tr><td>Is separate sustained-overvoltage protection required?<\/td><td>\u25a1<\/td><\/tr><tr><td>Does the documentation match the exact SPD model?<\/td><td>\u25a1<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Domande frequenti<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Does an SPD Protect Against Overvoltage or High Voltage?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">An SPD primarily protects against <strong>transient overvoltage<\/strong>, such as short-duration surges caused by lightning effects or switching events. It should not automatically be treated as protection against every temporary or sustained abnormal supply voltage. If the supply voltage remains excessively high, separate voltage monitoring or disconnection protection may be required.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Can an SPD protect against temporary overvoltage?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">It depends on the SPD and the specific TOV condition.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The datasheet or manufacturer documentation may specify TOV withstand or behavior for defined voltage, duration and connection conditions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Do not assume that every SPD will survive every TOV.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">What happens if mains voltage stays above the SPD&#8217;s Uc?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The result depends on how far the voltage exceeds Uc, how long it lasts and the SPD design.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In an MOV-based SPD, excessive continuous voltage can increase MOV current and heating.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This may eventually cause thermal disconnection or damage.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Is TOV the same as a lightning surge?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A lightning-related surge is a short transient event.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A TOV lasts much longer and is usually associated with a power-system abnormality.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The stresses placed on an SPD are therefore very different.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Does Imax tell me the TOV capability?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Imax is a surge-current parameter.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">TOV behavior must be evaluated separately.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Does a 40 kA SPD protect against a 400 V overvoltage?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">That question cannot be answered from <strong>40 kA<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">You need to know the nominal system voltage, Uc, connection mode, TOV declaration, duration of the abnormal voltage and the SPD design.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Can an SPD prevent damage from a broken neutral?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Do not rely on an SPD alone.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A broken or displaced neutral can create dangerous abnormal phase-to-neutral voltages.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Neutral integrity must be restored, and where required a dedicated voltage-monitoring and disconnection function should be used.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Can a circuit breaker replace an SPD?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A conventional circuit breaker protects primarily against overcurrent and short circuit.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">An SPD limits transient overvoltage.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">They perform different functions.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Can an overvoltage relay replace an SPD?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A voltage-monitoring relay can detect abnormal RMS voltage and initiate a switching action.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It does not replace the high-speed surge-diversion function of an SPD.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Conclusione<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Quindi, <strong>does an SPD protect against overvoltage?<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The technically correct answer is:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>An SPD protects against transient overvoltage, but it should not be treated as universal protection against every temporary or sustained abnormal voltage condition.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Surge current ratings such as <strong>In, Imax and Iimp<\/strong> describe transient performance.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Uc\/Ucpv<\/strong> describes continuous voltage compatibility.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Su<\/strong> describes surge-voltage limitation.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">And <strong>TOV behavior<\/strong> describes how the SPD responds to a specified temporary abnormal-voltage condition.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">These parameters should never be treated as interchangeable.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Real-world research also shows why the distinction matters. NIST\/EPRI investigations found dramatically different SPD responses to temporary-overvoltage conditions, ranging from survival to internal failure depending on the device and the applied stress.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The practical rule is simple:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>First identify the electrical event. Then select the protection function.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Use an SPD for transient surge protection.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Use appropriate voltage monitoring or disconnection when persistent abnormal supply voltage must be detected and removed.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">And if SPDs repeatedly fail, investigate <strong>system voltage, neutral condition, earthing, Uc\/Ucpv and TOV conditions<\/strong> before simply replacing the module again.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For PV applications, always verify the exact SPD model against the system&#8217;s maximum DC voltage, PV topology and applicable IEC 61643-31 requirements.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>","protected":false},"excerpt":{"rendered":"<p>Does an SPD protect against overvoltage? Yes, but the answer depends on what type of overvoltage is involved. A surge protective device is primarily designed to limit transient overvoltage, while temporary overvoltage (TOV) and sustained abnormal voltage require a different analysis. The phrase \u201covervoltage protection\u201d can be misleading, because not every overvoltage is a transient [&hellip;]<\/p>\n","protected":false},"author":7,"featured_media":4578,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[35],"tags":[],"class_list":["post-4577","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/posts\/4577","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/comments?post=4577"}],"version-history":[{"count":1,"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/posts\/4577\/revisions"}],"predecessor-version":[{"id":4586,"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/posts\/4577\/revisions\/4586"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/media\/4578"}],"wp:attachment":[{"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/media?parent=4577"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/categories?post=4577"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cnkuangya.com\/it\/wp-json\/wp\/v2\/tags?post=4577"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}