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tri cal elec

Bit of a first post but Ive encoutered some dangerous going on today at work. Im not the finished article and im not here for no, if you dont know what your doing you shouldnt be doing it malarky. If any one can tell me what the ---- is going on it would be most appreciated.

The job is a lights gone out with a big bang heard in a toilette. So me and my more knowledgeable! collegue attend the job.

What I found was a first.

Haveing flicked the breaker on it wasnt the lights that seemed to be the problem but only some sparks comeing out of a piece of conduit. There is a blanked of what I presume old light switch. After the mcb had been turned on after about 20 seconds you would start to here popping and crackling going on it the conduit, then after 40 seconds of this it would backfire sparks and a flash out of the bottom of it. Its been fine for ages at least 2 years. I notticed that someone has put up some surface mounted trunking on the wall and screwed it to the wall with raw plugs, the thing is they have only gone and done it slap bang onto of where the conduit is running under the plaster, honestly you could not have done it better if there was no paster. obviousy this is the problem or at least thats what im inclined to think. however as I say its been fine for at least 2 years no one in the team has never had a problem with it and the surface mounted trunking has not been recently put up certainly not in the year ive been there.

Any way if your still following and not enranged my thinking is this

For what ever reason the fact that someone has gone and drilled a piece of trunking to a wall falling slap bang in the middle of some metal conduit burrried in the wall which is carrying three lives to a old blanked of light switching point has now affected the instilation. some where along the circuit there is a live leakage. what i mean is that the nick in the cable or cables is causing the electricity to leak out of the conductor which is all the cracking which can be heard in the conduit and the bright spark whihc fires out of the end of it.

What would you hae done just so I can clock if they actually no what they are doing
 
im not here for no, if you dont know what your doing you shouldnt be doing it malarky.

Haveing flicked the breaker on it wasnt the lights that seemed to be the problem but only some sparks comeing out of a piece of conduit.
After the mcb had been turned on after about 20 seconds you would start to here popping and crackling going on it the conduit, then after 40 seconds of this it would backfire sparks and a flash out of the bottom of it.

The criticism you seek to avoid is frankly all you deserve.
 
Sounds like a live fault to the conduit which has poor continuity to earth which is restricting fault current and preventing the protective device tripping, got that.
 
The criticism you seek to avoid is frankly all you deserve.
i disagree some members seem to enjoy trolling op's who they feel know less than them . In some cases it fair to suggest to get a electrian in etc ,but alot of the time it just to belittle people . I enjoy the forum but was a bit weary posting the first time as i didn't want to get into daft arguments and come out feeling i know less than i did before post as i think it should be the other way around .
 
That strange , because in the two minutes since my last post i look at the gardens wise box post and you started the "are you a spark, not part P , it up to you and the custom marlarky
 
It seems to me this internet malarkey can be helpful and at times brutal for trainees
In the past the only one to knock some sense into you was the sparks who trained you,these days the knocking of sense can become a onslaught by the masses :)

Those who may have been upset can always take comfort
I have yet to meet anyone who knew what they were doing when they first set foot on the path to becoming a spark ;)
 
thank you westward sounds like what I was thinking. I find it weird that it has just started happening having been fine for ages. Its not as tho the trunking has only recently been put up by someone its been there for ages. But I guess now is the time thats its decided to show up which is another can of worms perhaps.

assuming there live as in part of the lighting circuit not not isolated, the only way to fix this is to find where the cables go into the conduit from above and pull them out and cut them back

I think this is gonna be a perfect time to bust out me old regs book and check the reccomened trip time for the device, then suggest the continuity of the conduit might be a bit shabby and look to improve this. how can I test the continuity of the conduit incase they dont know and how can I improve it other then checking things are tight

Im use to testing if something is live by going l-n l - e usually with something to put the probe into eg a connector block but in this case there are just three lives at the old switch point. no earth and no neutral so Im just going to be putting my probe onto the conduit for an earth right
 
If it is an unused part of the lighting circuit then removal would be a good idea, but you would need to be sure you maintain continuity of the lighting circuit to other areas if the line is looped at the switch.
It sounds like the circuit is arranged using the conduit as the earth for the circuit so a contact voltage tester from line to conduit should show the line voltage if the conduit is earthed.
You can do an R2 long lead test on the length of the conduit run to test its integrity.
The attached document gives nominal expected resistance of conduit to compare against.
I would ensure you have resolved the fault before you switch on the circuit again, it sounds like there is significant contamination somewhere that will only get worse.
 

Attachments

  • Impedances of conduits and trunking.pdf
    133.3 KB · Views: 8

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