Does electricity surge damage house wiring?

Wiring insulation may be damaged by a very serious over-voltage (it's not clear how large a surge they're talking about). Ultimately arcing could cause some plastics to carbonise and others to melt.

The main (and other) fuses may blow, depending what high current devices are switched on and whether they draw more current as the voltage rises (some do, some don't).

Any appliance plugged in at the time is also suspect, and even if not obviously damaged might have its lifetime shortened.

MM formulated on Sunday :

Very unlikely to damage the wiring, the fires were probably the result of equipment fed with too high voltage bursting into flames.

In message , Harry Bloomfield writes

Isn't there a CE requirement for withstanding overvoltage ?

Quite I'd be in touch with my insurers both contents for connected equipment and buildings for the fixed wiring to see what they say (in writing). You wouldn't want them coming back a few years down the line saying that you aren't covered for the fire caused by the TV or a fault in the fixed wiring that they say was caused by the surge.

I'd expect the insurers to want at a minimum a full installation test and PAT testing of kit that can be PAT tested.

proportion of properties in highly likely.

Regards

Steve Dawson

Stephen Dawson has brought this to us :

Modern mains wiring will normally withstand several thousands of volts, before breaking down. The only large scale breakdown of wiring insulation I have seen was due to lightning strike. I have seen lots of damage to appliances due to over voltage.

If there was a fault in the the supply wiring where 2 or more phases came together, you may see 415V AC for a short time, that could cause a few problems for the end user! The quality of some electrical equipment can be a bit suspect. It has happened in the past though the leccy boards have a habit of denying liability!

Des

The report says "[Scottish Power] Workers are also conducting door-to-door inquiries to discuss potential compensation claims with residents." so it sounds like it was a massive surge and the company wants to preempt a major outcry. I wonder what an insurer would say, faced with a claim to replace a new 42" modern TV, when told that there had been a power surge just before it went phut.

MM

Electricity meters are designed/approved to withstand a 6kV surge, so I would be amazed if any failed.

Jon.

"Surge" in this context tends to refer to transient overvoltage on a time scale of a few tens of microseconds, such as can occur when lightning strikes nearby. OTOH this thread seems to be about one of those sustained fault conditions in the supply network such as an open circuit neutral or crossed phase and neutral which results in some houses receiving close to the full 400 V line voltage of the 3-phase system for a long period.

An insulation test should tell you if there's a problem, for both appliances and fixed wiring. If the insulation is shot all over the place then a total rewire is the only solution, and leaving it not done would be a fire risk. Test at 500v/1kV, not 9v.

NT

Fuses don't stop surges. First the surge exists everywhere in a circuit. Eventually, a fuse blows long after the surge was ongoing. Generally, blows as a result of the damage . Fuses are to protect humans from further damage such as fire.

Depends how large that transient voltages is. Locally, a 33,000 volts wire fell upon a 4,000 volt distribution wire. 240 volts could have risen to 2000 volts. Probably higher since meters exploded upwards of

Some suffered appliance damage. Others did not. GFCIs (RCDs) were also victims. Some circuit breakers tripped; others did not. No wire damage was identified. In this case, no fires were apparent.

One homeowner with 'whole house' protector had no damage other than an exploded meter and damaged meter mounting pan. Of course, that 'whole house' protector protected household wiring as well as appliances.

NOw look what you've done. You've set w_tom off again.

It hasn't happened here yet and probably never will, as this was doubtless a one-in-a-million event. Nevertheless, it is useful to know what the response of (a) the insurers and (b) the power company would be. For example, whether the power company might cough up for a new meter but wash its hands of any house wiring claims (or for appliances).

MM

True. But w_tom is in the USA, so apart from the fact that he bangs on about his hobby horses and you get no useful information, power companies may have different attitudes there!

I don't see it as irrelevant, here a broken 25kv overhead line could drop onto a post-mounted 400v transformer output terminals. Probably highly unlikely, and I'm sure structures are designed to minimise that possibility. But I would be surprised if power distribution companies hadn't tested the probable consequences and figured out how they would clean up the mess.

"A Scottish Power spokesman said: 'An extremely rare underground cable fault caused the damage.' "

MM

An insulation test should tell you if there's a problem, for both appliances and fixed wiring. If the insulation is shot all over the place then a total rewire is the only solution, and leaving it not done would be a fire risk. Test at 500v/1kV, not 9v.

NT

Don't test at 1kV test at 500V.

Rgds Steve

It is a rare event. However so destructive that designs must take into account this event. As another noted, meters typically contain a spark gap to limit these voltages.

A 33,000v line shorted to distribution caused hundreds of meters to literally explode from the pan. Local power utility blamed this fault on lightning. As an act of god, the utility denied responsibility. Rules may be different in Scotland.

Many who had appliances on plug-in protectors had damaged appliances and destroyed protectors. One who had a 'whole house' protector only had an exploded meter and would have had all internal wiring protected.

Some got stuck for $thousands in damage. Others strangely had marginal damage or only tripped circuit breakers. Unknown how high the actual transient was or if any household wiring was affected. But no fires occurred during this event or after power was restored.

What was voltage on that Scottish Power underground line? Numbers provide a useful upper limit.