Bang!

[Delboybully]

So I go to a job a couple of days ago in a small shop. One of the things to do is fix an RCD that isnt working in a dual RCD board (not that neat but ok, no labels), everything works but if you turn the RCD off it doesnt disconnect the supply to the 4 MCBs it covers. Also the test button doesnt work. Take the cover off the board and the RCD isnt bypassed, it looks like it has failed closed.

I do a quick Ze, turn off the MCBs, RCDs and the main switch, test for dead and replace the RCD. I then power up and the replacement RCD trips. So I then start doing combined IR test L+N to E for each circuit to find the offending circuit. MCBs 1,2 and 3 or ok

Which leaves circuit 4, I connect my jump lead to neutral and the live and BANG!!!!! Nice pirotechnics with a few bits of hot metal spraying around!
Luckily my jump leads have a plastic covering on them or I could have got a belt!

I can tell you I wasnt expecting that. Luckily my jump leads have a plastic covering on them or I would have got a belt! My apprentice missed the fireworks as he was getting stuff from the van but he was impressed with the jump lead afterwards with a bit missing and the charring on the live cable

So I do some more investigating and it turns out the cable coming into the MCB was live and coming from the upstairs flat and was feeding the other 3 circuits in the shop through the bus bar. The guy in the flat above (luckily he was in) told me he has been getting electric bills of roughly a grand every 3 months, no wonder he had been paying for half the electric bill for a small cafe.

Now I followed the safe isolation procedure as I always do but this still happened. I phoned the Elecsa technical helpline and the guy said you followed the safe isolation procedure and its just one of those things you occasional see. He suggested waving a volt stick around the board in future. I then needed to phone the technical helpline again today on another matter so I asked the new guy the same thing, he again said that there isnt much you can do about these things.

I am one of the hated 5WWs, been doing this for approx 2.5 years. I am prepared for a slating, however I would be interested to learn how any of you would of approached this problem and would you of ended up in my situation. Obviously I followed the correct isolation procedure but still ended up in an undesirable spot. Any suggestions would be appreciated

Del

 

[telectrix]

do your isolation business, then use you approved voltage tester. 1 end on E and then prod all the MCBs and busbar with the other. many a time i've almost been caught with a missing neutral. you test l-n and get no reading.

 

[Deleted member 72666]

But you didn't follow the safe isolation procedure did you?

 

[guest119]

I suggest you read up on safe isolation proceedures before you hurt yourself or another.
What were you doing working in a commercial environment?
Do you consider yourself suitable to train, and keep safe, an apprentice?

Boydy

 

[Clive P]

Hi,

To be honest, I think most of us will have carried out isolations this way.
Turn off all the MCB'S , RCD's and main switch and test. I can't believe that EVERYBODY checks every single circuit on every isolation. For my part I think the OP was getting a bit of a slating; when it's not really due. Good point is, it has reminded us all that you can't take everything for granted.

Regards.

 

[Meggerman]

You have done what most others on here would do on here to be honest. You don't need slating at all mate. Whoever wired those DB's together like that needs slating big style.

 

[Delboybully]

Obviously it is a lesson learnt for me and I shall be doing as Tel suggested from now on. Thanks to clive P for an honest reply.

 

[sparks1234]

We all get a belt from time to time, it goes with the business, no need for any sort of slagging because you are a Electrical Trainee its just the way it is. Fair play to you though for admitting it.

 

[Badged01]

I'll give you your due and tip my hat, it takes some b*lls to openly admit a 'misteak' and being a "Electrical Trainee" at the same time on this forum. Sure as eggs are eggs you know there will be a bunch of members just queuing up to give you a good shoeing for doing so!

Glad your safe, lesson learnt, move on .....

 

[MDJ]

I'll give you your due and tip my hat, it takes some b*lls to openly admit a 'misteak' and being a "Electrical Trainee" at the same time on this forum. Sure as eggs are eggs you know there will be a bunch of members just queuing up to give you a good shoeing for doing so!

Glad your safe, lesson learnt, move on .....

hellooooooooooooooooooo :smilielol5:

 

[southsea1201]

Well let's hope that people don't slag off the OP. He'd done everything but pull the main fuse and even that wouldn't have negated the outcome. It's a lesson for everyone that putting your voltage tester on the main switch means nothing...and that's something 99% of people do...remember the saying " familiarity breeds contempt"....I would be sceptical of even the most experienced sparky who claimed he'd never had a belt or a mishap in his life.
One thing you don't need to do is put down the OP because it will stop further postings of this nature, and it's by sharing experiences we all learn. Well done the OP for a great post.

 

[Marvo]

I also have some sympathy for the OP with this one. Unless you test every single MCB plus the neutrals and even any disconnected cables there will always be a chance of a nasty surprise. Last time I got one was several years ago, there was a disused cable in a DB I'd just isolated and tested for dead, it was laying in the bottom terminated in a choc connector. It turned out to be a feed from a small UPS that was running back into the DB. I didn't get shocked but it cost me my favorite pair of side cutters.

 

[telectrix]

the much maligned voltstick casn be useful in these situations. if it lights, then further investigation , with caution, is the way forward. we've all been caught out, or nearly caught out. as said in an earlier post. familiarity breeds contempt.

 

[Knobhead]

I’ve deliberately had to back feed LV boards several times. Always down to UG cables being damaged. Each time it was documented and warning notices posted. It’s easy on an MV “open ring” it’s designed for it, LV systems it gets a bit more complicated.

 

[itselectric]

Three positive things have come from this, even though by accident. Firstly you have found a fault which could have resulted anyone following on being electrocuted. Secondly you have saved the tenant a lot of money and, thirdly, you have learned a good lesson for the future. As others have said we have all been there with complacency.