In the context of whole house protection devices used in distribution panel, if an MCB protects from overcurrent, which device protects from overvoltage?

Surge Protection Devices (SPD) can only protect from transient overvoltages before failing. Temporary overvoltage (TOV/Ut) withstand capacity for an SPD with rated voltage of 230V is often 330-440V for 5s.

Is there a circuit breaker that trips from overvoltage?

  • \$\begingroup\$ "... rated voltage of 230 V is often 330 - 440 V for 5s." Are there published figures for that? I'd be very surprised to see that on mainland Europe. We don't even have problems like that on the relatively small (5 GW) Irish grid. Most domestic and industrial setups could not tolerate that. \$\endgroup\$
    – Transistor
    Jun 16, 2019 at 14:08
  • \$\begingroup\$ @Transistor Dehn 952 400 Type 2 SPD has Un = 230V and Ut = 335V. Datasheet: dehn-international.com/store/f/181155/Artikelnummer_PDF/… \$\endgroup\$ Jun 16, 2019 at 15:05

1 Answer 1


Over-voltage protection is mostly provided in the design of the generation, transmission and distribution system. There are over-voltage, under-voltage, phase-loss, frequency deviation and other protections provided at the substation level. Large industrial facilities may have such protections at the utilization level, but they essentially have their own substations and may be serviced by more than one transmission line. Residential, commercial and most residential installations depend on the utility to provide that protection. Some facilities with emergency power generation have such protections.

The protection devices are generally called protection relays. Protection relays may interrupt power through the use of shunt-trip or motor-operated circuit breakers. The overall design of power distribution protection systems is an extensive area of study.

  • \$\begingroup\$ Thanks, assuming the local power distribution company lacks voltage regulation systems, should a residential voltage protection relay be installed before or after an SPD? I see sort of a chicken/egg problem here. If a voltage protection relay is installed before an SPD, then it will be damaged during transient voltage spikes that only an SPD could handle. If after the SPD, then the SPD would fail in case of sustained overvoltage. \$\endgroup\$ Jun 16, 2019 at 13:51
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    \$\begingroup\$ The voltage protection relay may withstand transients that it doesn't protect against. Check the specifications. SPD may be needed both before and after the relay. SPD devices are often considered expendable like fuses. \$\endgroup\$
    – user80875
    Jun 16, 2019 at 14:09

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