Direct current systems such as solar PV strings, battery energy storage, telecom power plants and DC industrial busbars carry high fault energy and face frequent lightning and switching surges. A Type 2 DC SPD, built and tested to IEC/EN 61643-31, is the standard device for limiting these overvoltages. But a surge protector is only safe when it is coordinated with the upstream DC circuit breaker or a dedicated backup protector. Coordination means the protective chain clears a faulted SPD without interrupting normal operation during a surge.
Britec Electric has manufactured surge protective devices since 2003 and supplies a complete Type 2 DC SPD portfolio for 48V up to 1500V DC systems. This guide explains what coordination really means, why a plain AC breaker is not enough, and how to select backup protection that keeps your DC installation safe.
A DC circuit breaker is sized for the load current and the wiring short-circuit rating. It is not sized for the limited short-circuit withstand of the SPD. When a Type 2 DC SPD is stressed by a temporary overvoltage (TOV) or a surge that pushes it into thermal runaway, the resulting follow current can sit below the breaker’s magnetic trip threshold. The breaker then stays closed while the SPD overheats, smokes or fails.
DC is also harder to break than AC. A standard AC miniature circuit breaker (MCB) may not quench a DC arc reliably because DC has no natural current zero crossing. Using an AC breaker on a DC circuit is a common and dangerous coordination mistake.
Two numbers decide coordination. The first is Imax, the maximum discharge current the SPD can absorb (for example the BR-40 48 Type 2 DC SPD is rated at Imax 40kA, 8/20us). The second is Isccr, the short-circuit current rating of the SPD, or the maximum fault current the SPD can survive until backup protection clears it. In most DC SPDs Isccr is far lower than Imax.
If the prospective short-circuit current at the SPD location exceeds Isccr, the SPD can be destroyed unless a backup device opens fast. IEC/EN 61643-32 governs the coordination and selection of this backup protection. Britec’s dedicated SPD backup protector (SCB) is engineered for exactly this job: it passes surge currents but disconnects follow and short-circuit currents the SPD cannot withstand.
Engineers have three proven ways to coordinate a Type 2 DC SPD with upstream protection:
● Use a dedicated SPD backup protector (SCB) — an SCB sized to the SPD’s Isccr is the cleanest coordination. Britec BRSCB models are matched to Class I and Class II SPDs and sit in series with the SPD on the DIN rail.
● Combine the SPD with a miniature circuit breaker — integrated modules such as the Britec SPD combined with a miniature circuit breaker (BRCB TP) pair a Type 2 SPD and a DC MCB in one compact unit, removing guesswork from coordination.
● Add a coordination inductor — a BRCI coordination inductor limits the rate of current rise (di/dt) between cascaded SPDs so a downstream device is not overstressed by a nearby upstream event.
Use this checklist when specifying coordination for a new or existing DC installation:
● Identify the DC system voltage and polarity — 48V, 60V, 1000V or 1500V PV bus; select a Type 2 DC SPD whose Ucpv exceeds the maximum continuous DC voltage.
● Read the SPD’s Isccr and Imax — confirm the backup device clears any fault above Isccr but below the SPD’s thermal damage limit.
● Specify DC-rated breaking — choose a DC MCB or an SCB certified for the DC voltage; an AC MCB is not acceptable.
● Match the SCB to the SPD class — Britec BRSCB Class I and Class II models are sized per SPD type for clean coordination.
● Document the coordination — record the calculation per IEC/EN 61643-32 and keep it for inspection and warranty.
In solar PV, string and array PV surge protection devices such as the BRPV3-1000 (up to 1000V) and BRPV3-1500 (up to 1500V) sit inside combiner and inverter DC boxes. Each SPD must be coordinated with the combiner box DC breaker. A coordinated SCB prevents a single failed string SPD from taking down the whole array and reduces arc-flash risk during maintenance. The same logic applies to battery energy storage and DC charging infrastructure.
Britec’s full DC surge protector range covers 48V control systems through 1500V utility-scale PV, all with DIN-rail mounting and green/red status indication.
● Reusing an AC MCB for DC — AC breakers can fail to clear DC arcs; always specify DC-rated protection.
● Ignoring Isccr — when available short-circuit current exceeds the SPD rating, add an SCB or the SPD becomes the weak link.
● Oversizing the breaker — too high a rating defeats coordination and leaves the SPD unprotected during thermal runaway.
● No status indication — choose SPDs with visual green/red windows and remote signal so faults are caught before they escalate.
What does coordination mean for a DC Type 2 SPD?
Coordination is the practice of pairing the SPD with an upstream DC circuit breaker or dedicated backup protector so that, if the SPD fails or draws follow current, the backup device disconnects it safely without tripping during normal surge events.
Can I use a normal AC circuit breaker with a DC SPD?
Not safely. DC has no natural current zero, so an AC MCB may not quench the arc. Use a DC-rated breaker or a dedicated SPD backup protector (SCB) matched to the SPD’s Isccr.
What is an SPD backup protector and do I need one?
An SCB is a protective device tuned to the SPD. It carries surge currents but opens on follow or short-circuit currents the SPD cannot survive. You need one whenever the prospective fault current at the SPD exceeds its Isccr.
What is Isccr and why does it matter?
Isccr is the short-circuit current rating of the SPD, the maximum fault current it can endure until backup protection operates. Coordination fails if the available short-circuit current is higher than Isccr, so the SCB must clear faster than the SPD is damaged.
How do I coordinate an SPD in a PV combiner box?
Size the PV SPD to the string voltage (Ucpv above max DC), read its Isccr, then place a DC-rated breaker or SCB in series. Verify the combination per IEC/EN 61643-32 and keep the calculation on file.
Does Britec provide DC-rated backup protectors and combos?
Yes. Britec Electric supplies dedicated backup protectors (BRSCB Class I and Class II), SPD plus MCB combos (BRCB TP) and coordination inductors (BRCI), all designed for DC surge coordination and supported by engineering documentation.
Coordinating a Type 2 DC SPD with the right DC circuit breaker or backup protector is what turns a surge protector from a liability into a reliable safety device. Size to Isccr, specify DC-rated breaking, and document the result per IEC/EN 61643-32. Britec Electric supports B2B buyers with matched SPD, SCB, MCB-combo and inductor solutions across 48V to 1500V DC systems.
Need a coordinated DC SPD and breaker solution?Britec Electric helps B2B buyers size Type 2 DC SPDs with matching backup protectors for PV, telecom and industrial DC systems. Talk to our SPD specialists for a datasheet, coordination drawing and quote.
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