When all looks good but .....

[westie101]

A colleague was called to a loss of supply this morning, attended soon after our starting time and found a house with the 100A cut-out fuse blown, and no evidence why.
Customer stated they had gone to bed last night with the supply OK and got up this morning to no supply.

So being a careful guy he switched all the MCBs and a RCBO in the Ashley CU to off
Switched the incomer to the CU to off

As a precaution he fitted some 5A fuse wire to the cut-out fuse carrier and wearing the necessary PPE put the fuse carrier back in.

All seemed fine

Switched the CU main switch to on and BANG, big BANG as the fuse blew

After a careful inspection he decided to try again, with the same result.
But this time inspection showed some evidence of blackening on the CU in the vicinity of a 32A RCBO (an old type as it took up 2 spaces on the CU)

Against the rules, but that's what we do guv, he disconnected and removed the RCBO and was then able to restore all other supplies. As he left the customer was arranging to have the CU replaced.

So watch out for some older RCBOs

 

[deadshort]

Are we talking 80's or earlier ?

Regards, DS

 

[westie101]

Are we talking 80's or earlier

Possibly

 

[Lectrician]

I had a call out to no supply, got there, customer said DNO had been, said not their problem, and left.

I assumed they had done nothing.

Turned on the tripped main RCD, and bang. DNO fuse blown.

Turned out RCD was faulty. DNO had replaced fuse, turned on RCD, it went bang. They left it off, replaced fuse and left. No comments, no note, no log with their control.

Would say this DNO chap was not quite as consencious as yours!

 

[deadshort]

I had a call at 5am from a client stating that the lights in her flat had been flickering the previouse evening and she had called out the DNO at 10pm the prevoiuse night.They removed the fuse for the lighting circuit and said the fault had been 'removed' and she should get an electrician to rectify the fault.

When i arrived at 5.30am she said she was concerned as she thought she could smell burning, when i opened the new cupboard which had been build to cover the CU i found the top of the cuboard alight and the architrave around the front door smoldering. (The fault was disconnected aparently!)

The joiner who build the cupboard had put 3 screws through the one leg of the RF and it had been arching for days.

What's an IR tester

Regards,

DS

 

[mikeyd]

....he disconnected and removed the RCBO

I would never have thought anything other than serious physical damage could cause a line/neutral short 'good enough' to pass 100A without blowing itself apart first. Where is the RCBO now? Will anyone be disassembling it to see how it failed?

 

[JohnW2]

I would never have thought anything other than serious physical damage could cause a line/neutral short 'good enough' to pass 100A without blowing itself apart first. Where is the RCBO now? Will anyone be disassembling it to see how it failed?

I'm not sure whether you were around when I reported what happened to an RCD in my daughter's CU when she pressed the test button (unfortunately, she's now saying "never again"!) - a very loud bang, a cloud of black soot and a blown 80A DNO fuse, but the RCD still looked essentially intact (externally!):

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• 20 Apr 2013
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... and the cause was this - the insulation obvious managed to get chopped by something when the mechanism operated:

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• JohnW2
• 21 Apr 2013
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Kind Regards, John

 

[westie101]

Where is the RCBO now? Will anyone be disassembling it to see how it failed?

Left with the customer so I doubt it.

Perhaps that and with John W2's RCD it shows that the enclosure has done it's job and contained the blast.

 

[ban-all-sheds]

(unfortunately, she's now saying "never again"!)

You'd better go round there with your tester every now and then.

 

[deadshort]

(unfortunately, she's now saying "never again"!)

You'd better go round there with your tester every now and then.

All does not looks good but ……. Protek ??????

I would have expected a quality brand from you John!

Perhaps Santa will bring a Hager from dad

Regards, DS

 

[JohnW2]

(unfortunately, she's now saying "never again"!)

You'd better go round there with your tester every now and then.

In the first instance, I'll probably just take my 'test button finger' around every now and then - I don't think that sort of lightning is likely to strike twice in the same place, and it's the first time I've heard it happening to anyone, anywhere, so I probably have statistics on my side!

Kind Regards, John

 

[JohnW2]

All does not looks good but ……. Protek ?????? ... I would have expected a quality brand from you John!

'Twas not me wot installed it, m'lud

However, I wonder which you would have considered 'worse'- my having installed a Protek board (which I didn't do) or what I actually did (on a rapidly darkening Saturday evening, to get the installation back on) - namely replacing the RCD with a Wylex one (and I won't mention the tweaking of the busbar that was required!), given that Protek RCDs are not something I keep on my shelves!

Kind Regards, John

 

[EFLImpudence]