Changing CU during thunderstorm

[oo7]

Stick with me here guys...

So yesterday I changed an old rewirable CU for a nice duel RCD protected system. This morning I return to the property to be greeted by the very excited owners telling me that there was a big explosion last night and all the power went off (I could have crushed a golf ball between my arse cheeks at this point).
Anyway after making me sweat for some time they finally get round to telling me that it was a lightning strike and that both the neighbours, who are on old rewirable CU, have no power still but all they had to do was reset there RCD. Great! (Although it's blown a free view TV and a receiver) .

But now that I've thought about it I've been left wondering "what if I had still been installing the CU at the time of the strike?" All those cables hanging out of the wall waiting to be reconnected, MPB not connected to the MET.

I know the chance of this happening whilst changing a unit are slim but the severity of the potential hazard leaves me thinking is it worth changing a CU when a good thunderstorm is due.

So what do you guys think, other than don't be such a pussy and get on with it?

Cheers,
Chris.

 

[ericmark]

In the UK lighting strikes are rare and can be split into three groups.
1) Near miss this can still cause damage as the voltages rise to huge values and can take out equipment but no structural damage as a result and very little one can do to avoid it.
2) Strike starting at bottom of thunder cloud which is the normal one.
3) Strike starting from the top of the cloud normally just a storm is about to pass which is typically 10 times the value of strike starting from bottom.
The last will almost every time cause structural damage as water in wet bricks boils even with lighting conductors damage can still happen.

Lucky for us the last two are very rare it's the near miss which is more common so with the power to house disconnected it is the flash over we are worried about so with an isolator fitted to the DNO supply the danger must be very low but where disconnection is only by drawing a fuse the chance of getting a connection to neutral must be a lot higher.

However I would never change a CU unit in a storm mainly because if the storm knocks out the supply to try to explain to owners it's not your fault is hard.

As to items connected to an aerial that is also a problem. We are told aerials should not be fitted to a sharp edge or to anything which has an earth track so do not fit to gable end of house or to a soot lined chimney but in the main that's exactly where we do fit them. Also should use de-coupling capacitors in the TV socket but this stops DC supply to mast head amplifier or sky box digi-eyes so one has to be wary of where plates with de-coupling capacitors are used.

But if we do a risk assessment then not driving a car would be far higher on the list of things to avoid and if you lived in USA then clearly you would do things a little different but in UK don't think we really need to worry.

 

[bernardgreen]

A former colleague was standing by a rack of communication equipment when a crackling sound and smoke came out of a module. The module terminated a private wire ( direct phone line ) to a site several miles away. There had been a near miss lightning strike at that site and the private wire had been lifted to a potential high enough to bridge the isolation barrier in the module which led to more damage in the module.