Fitting a ceiling light.

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Paul555

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Hi all..
Not woodwork but on the off chance some of you knowledgeable guys may be help, I could do with some advice regarding an electrical job I was doing today. Wife wanted to replace both sets of 4-track ceiling lights at either end of the kitchen. I turned the power of at the mains..didn't try to isolate just the lights, I turned the entire house off just in case...
First one was no problem...red, black & earth coming from the ceiling, connected to brown, blue and earth on the light fitting. Worked perfectly.
Second one looked a little different...2 reds, 2 blacks and earth coming from the ceiling. Got my little screwdriver, disconnected all of these from the existing light fitting block and away it came from the ceiling without a problem.
This is the point it all went a bit wrong. As soon as I grabbed hold of all 5 of these wires to feed them through the mounting bracket in much the same way as I had done with the 3 wires in the first light I got a shock. Not a full blown mains shock (I know what they feel like!) but certainly enough to hurt.
My question is...how is this possible if the power to the whole house is turned off at the consumer unit? Could it have been some kind of residual power that was just waiting for some mug like me to earth it or is it more likely that I have completely overlooked something and was only saved from a full mains shock because I was standing on rubber treaded steps in rubber soled slippers?
Any advice gratefully received before my next mistake is my last...:)
 

Gordon Tarling

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Did you check anything was live before you disconnected those lights? NEVER assume that the switch you used is the one that isolates that which you plan to disconnect - switch off, then check before you touch anything!

G.
 

Spectric

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Ideally you should use a certified tester to prove dead, but next best is to use a test meter, if the main switch is turned off then everything must be dead otherwise you have an issue and need to get an electrician in. Do you have any fluorescent light fittings ?
 

Paul555

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Ideally you should use a certified tester to prove dead, but next best is to use a test meter, if the main switch is turned off then everything must be dead otherwise you have an issue and need to get an electrician in. Do you have any fluorescent light fittings ?
No Roy, no fluorescent lights. As soon as I turned the mains switch off everything in the kitchen went off...side lamp, microwave, cooker, internet..everything. The TV was on in another room and that went off too. I;ve done a little bit of electrical stuff in the house in recent years...changed numerous ceiling lights & switches and I've always turned the same switch on the main consumer to "off" and never had a problem.
 

Lorenzl

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I found out the hard way that neutral can still be "live". Although I would have thought turning off the consumer unit would isolate live and neutral
 

Flynnwood

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I found out the hard way that neutral can still be "live". Although I would have thought turning off the consumer unit would isolate live and neutral

@Lorenzl Yes - a neutral can be a problem if it belongs to "borrowed neutrals". That took me a while to understand.

@Paul555 Are you sure there is not a secondary consumer unit fitted somewhere?
Have a look at John Ward on proving electrical dead:
 

Spectric

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I found out the hard way that neutral can still be "live". Although I would have thought turning off the consumer unit would isolate live and neutral
The mains switch is a double pole device and will take out all power, including borrowed neutrals. Look at your main incomer and follow it from the DNO supply fuse / meter and check there are no junction boxes that could split the supply to two distribution boards, unlikely but just worth ruling out. You say you got a shock, could this just be a circuit discharge that once gone it is now dead?
 

Paul555

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@Lorenzl Yes - a neutral can be a problem if it belongs to "borrowed neutrals". That took me a while to understand.

@Paul555 Are you sure there is not a secondary consumer unit fitted somewhere?
Have a look at John Ward on proving electrical dead:

Thanks Lorenz, and yes...there is another consumer unit in the garage well away from the house but I've always ignored it when I was working on stuff in the house, thought it was only there for the numerous plug sockets to run my tools, and like I said...I've never had a problem before. I'm going to have to get a proper electrician in to have a look at this for me before I do anything else. Thanks for the observation.
 

Paul555

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The mains switch is a double pole device and will take out all power, including borrowed neutrals. Look at your main incomer and follow it from the DNO supply fuse / meter and check there are no junction boxes that could split the supply to two distribution boards, unlikely but just worth ruling out. You say you got a shock, could this just be a circuit discharge that once gone it is now dead?
I don't know enough about it to guess Roy...maybe that's what it was. I'm going to get somebody in the check what's going on before I kill myself. :)
 

Henniep

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All the comments about testing circuits after isolation are 100% true! Pity the first post rapped your knuckles instead of offering friendly advice. Here's something someone may learn from. If your have any appliances that have battery back-up, you may get a sharp 12V DC wack back through the wiring after you've isolated the main incomer.
 

Ozi

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Just a word of warning - which I ignore myself - but us untrained folks are not now allowed to fit lights in kitchens or bathrooms as they are wetted areas and you could invalidate your house insurance. Be careful and good luck getting it sorted
 

cerro

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If its any help after pulling the fuses I check the fitting is not alive then a cross the live and neutrals as a safty precaution
 

Sandyn

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There might have been a switch mode PSU in the circuit somewhere and the input storage capacitor still had a bit of charge. There are also filter capacitors (X and Y ) The X capacitor can retain charge for a few minutes if there isn't a bleed resistor. Some manufactures might not fit bleed resistors to reduce cost, or to reduce leakage current.
 

Pedronicus

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Not meant as a criticism of the OP whatsoever (as I don't know his capabilities) but it never ceased to amaze me during my working life how most folk wouldn't go near plumbing works but quite happily played with electrics. If plumbing goes wrong it makes a mess whereas if leccy goes wrong it can kill! Maybe it is because one can't see electricity in it's raw state but water is visible every time a tap is opened.
 

Stevekane

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I can only speak for myself but I would just carry on hes done the job, didnt kill himself and learned a little as well. I also very carefully touch a neon screwdriver on the wires just in case, and I know its not a fancy tester but its an indication, and then gingerly short the wires to be doubly sure although I really wouldnt want it to be live as I expect it would be quite a bang!
I might also be wrong with this but I think changing or replacing existing fittings is fine for DIY?
Steve.
 

MorrisWoodman12

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Agree with @Sandyn above. Many devices have an X capacitor (across L to N) fitted to reduce radio frequency noise going back down and using the mains lead as an aerial. They can give a fair jolt ( I'll let you guess how I know) especially if several devices are plugged in just waiting for some sucker one to connect himself. You are unlikely to feel 12V from a battery backup as it will not penetrate the skin's natural insulation. That's why the LV directive scraps most requirements below 42V.
I won't suggest trying it again but I will hazard a guess that it is now dead.
 

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