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Topic Title: Surge taking out (almost) whole building installation.
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Created On: 07 November 2012 07:26 PM
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 07 November 2012 07:26 PM
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Posts: 682
Joined: 09 March 2012

I got a desperate call this morning from a local childrens nursery - "our heating isnt working, we've had some electrical problem overnight, and now the heating wont come on".
Ok, I dropped my stuff and went straight over, to find the full story.
Eon had just left, there had been a voltage surge, and they had traced the fault not to the local sub-station, or a damaged cable, but to the neutral busbar (more of an Henly block), inside the building, just after the cut-outs, in a TP+N switch.
The 25mm cable had melted the insualtion for around 3 inches, and left a lot of welding style splatters around the henly block. It was all sealed up when I arrived, so I didnt see the damage inside the box.
Onto the heating, luckily, an easy fix, the programmer had blown, so a few wagos linking wires inside the box had the heating on, until a new programmer was fitted later.
Then onto the rest of the building. Virtually everything that was connected to the mains was dead. A few flourescents had survived, and the oven, but 2 freezers, a fridge, 10+ phones, the router and computers, fire alarm, security alarm and many other smaller items were dead.
I reckon £5000 to repair/replace.
Now may be a good time for me to submit a price to fit SPDs.
I asked if they will be claiming on the electricians insurance who did the rewire in July, but, apparently he said he hadnt even opened the main switch box, which I found hard to beleive, but possible I suppose.

 07 November 2012 08:02 PM
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A good policy is to check and tighten all sub-mains terminals as you go. Sometimes not officially possible if they have been sealed up by the DNO.



 07 November 2012 09:01 PM
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If the fault was within a DNO sealed enclosure, then they would be liable for paying the compensation / replacing the failed appliances, just as if the fault was out in the street affecting a larger part of network. I would expect the DNO's representative to examine all the items in the property, then arrange for their replacement.

On the subject of SPDs, I am not sure that you would find SPDs with ratings that were appropriate for protecting against a broken neutral. You could of course use SPDs together with an overvoltage relay and shunt-trip on the main incoming device, but this is not really sensible in most cases.


 07 November 2012 09:54 PM
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Joined: 04 November 2004

Sounds like the single phase kit got the full 400v
when the neutral was lost, as Alan says SPD's won't help in this circumstance.


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