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

 

[southsea1201]

I've been at it for 35yrs and can honestly say "You learn something new every day." That's how you gain experience and you very often say "Oh bugger, I won't do that again."

Exactly, by sharing experiences we all learn more each day. I can see the impatience on this forum of the senior posters when others ask what they perceive as daft questions, and perhaps they have forgotten they were once the errand boy or teamaker. Now they have vast accumulated knowledge and at times can be a little condescending on more inexperienced people. Clearly they have forgotten their humble beginnings.
Knowledge takes time, and giving your knowledge is the biggest gift of all. We all love to read the occasional threads which show the fountains of knowledge some guys have...but it also seems they just can't resist giving someone a short kick in the nuts!!!!

 

[scammell man]

I think there's an aspect here that is overlooked. The tests are designed to be carried out in order to safely find faults. They are really designed for new build, ie everything starts dead. The tests don't work so well for fault finding and periodic testing, which is why 2395 is one of the highest qualifications. I am on record elsewhere on this forum for stating if you are Part P only you are not qualified for periodics or for offering a fault finding service.

in my view, the OP has made an early assumption which was wrong, and nearly killed himself. Also his powering down of the CU was at fault.

assumption: rcd faulty and was not. This was replaced and not tested. A functional test of the new one to prove the assumption would have shown the assumption wrong and further investigation was required. However he assumed fault fixed and ploughed into a full test of a system which wasn't dead. Golden rule: change one thing at time to prove cause and effect.

powering down CU. OP States no data. It would be better to identify what was powered down by each MCB as it was switched off. Ie identify the circuit. The false feed would be identified as Unknown which should equal warning. With an apprentice to run round the cafe and see what's happening this form of investigation is easy.
golden rule. Take your time.

If you think this is easy to say sitting on the computer, I had exactly this last week. Unlabelled CU with additional circuits added in. I spent 2 hours finding out what was on each MCB and where other supplies in the installation interacted before even thinking if putting my fingers on the copper.

 

[telectrix]

not a good ideas to put your fingers on a copper. you'd be up before the beak on an assault charge before you could say"only joking, occifer".

 

[m top]

I think there's an aspect here that is overlooked. The tests are designed to be carried out in order to safely find faults. They are really designed for new build, ie everything starts dead. The tests don't work so well for fault finding and periodic testing, which is why 2395 is one of the highest qualifications. I am on record elsewhere on this forum for stating if you are Part P only you are not qualified for periodics or for offering a fault finding service.

in my view, the OP has made an early assumption which was wrong, and nearly killed himself. Also his powering down of the CU was at fault.

assumption: rcd faulty and was not. This was replaced and not tested. A functional test of the new one to prove the assumption would have shown the assumption wrong and further investigation was required. However he assumed fault fixed and ploughed into a full test of a system which wasn't dead. Golden rule: change one thing at time to prove cause and effect.

powering down CU. OP States no data. It would be better to identify what was powered down by each MCB as it was switched off. Ie identify the circuit. The false feed would be identified as Unknown which should equal warning. With an apprentice to run round the cafe and see what's happening this form of investigation is easy.
golden rule. Take your time.

If you think this is easy to say sitting on the computer, I had exactly this last week. Unlabelled CU with additional circuits added in. I spent 2 hours finding out what was on each MCB and where other supplies in the installation interacted before even thinking if putting my fingers on the copper.

The guy made a mistake I don't understand your comment regarding the test don't work so well in fault finding why is that you can not find a fault with the dead test continuity insulation resistance ? Please explain you wouldn't look for a fault on a periodic live would you

 

[scammell man]

M top , I don't understand your question.
try this
what is the first test you do
was this done in this case

then try
how do you do an IR test on an unknown circuit. Have you removed all those nice expensive bits that don't like 500v up 'em?

has the OP killed himself, do you think HSE would say 'oh we'll be was faced with a difficult situation which he could not have foreseen and therefore there was nothing he could do' ? That's like saying your dead As soon as you accept the job and that is not so!

 

[m top]

Ok maybe I misunderstood your explanation what test do you do first on a periodic ,prove there's an earth ze identify cuircuits safe isolation dead tests to find any faults, I was not referring to this case in general just didn't understand what you were saying about the dead tests don't work so well for fault finding.

 

[telectrix]

why else would we spend all that money on vde 100v tested tools? it's not because we work live, is it? LOL.

 

[HappyHippyDad]

If it's single phase what's the difference as long you understand the cuircuit design why not core principle no different?

What you're saying is right in theory Mtop, but thats a bit like saying a competent nurse who has watched the doctor do thousands of operations could do it themselves. They might be competent to do it, but that doesn't make it right. I think its a bit of a slippery slope if we say.."well he's not qualified on paper, but he knows what he's doing". I think we need to work within both the 'legal boundaries' AND within our own competency levels.

That all sounds a bit boring but with 60 odd million people in the country there needs to be certain boundaries otherwise ther'd be chaos!! :dizzy2:

 

[scammell man]

An example: full test IR Line neutral
periodic or fault finding this is normally skipped because you don't know what's out there or you can't be bothered to remove several scores of bulbs.

 

[m top]

What you're saying is right in theory Mtop, but thats a bit like saying a competent nurse who has watched the doctor do thousands of operations could do it themselves. They might be competent to do it, but that doesn't make it right. I think its a bit of a slippery slope if we say.."well he's not qualified on paper, but he knows what he's doing". I think we need to work within both the 'legal boundaries' AND within our own competency levels.

That all sounds a bit boring but with 60 odd million people in the country there needs to be certain boundaries otherwise ther'd be chaos!! :dizzy2:

So your saying you would turn a job in a shop down because it isn't right ? Please don't think I am havin a dig but if you are competent you are competent this was a single phase supply so what's the difference,if it was 3 phase and you have not worked on it before ie in a shop that's different and if you are responsible would draw the line and not attempt the work even if you think you have an idea.

 

[scammell man]

You get 3 phase in houses. If you can't work on 3 phase you aren't competent. Period.

 

[m top]

An example: full test IR Line neutral
periodic or fault finding this is normally skipped because you don't know what's out there or you can't be bothered to remove several scores of bulbs.

Thanks on your level now lol totally misinterpreted your first post mate

 

[guest119]

Now we have the Electrical Trainee brigade arguing amongst themselves about competency, what next!

Boydy

 

[sparks1234]

So, is there anyone on here that has never ever had a belt?

 

[telectrix]

i was once thrown across the kitchen, but i divorced her soon after.