Another "impossible" fault thread
- Thread starter ProDave
- Start date
Help Support Talk Electrician Forum:
Manator
©Honorary Essex Boy™
I bet you can work it out.
get a pen and paper if you need to m4tty, or even several pages, it will soon become very obvious once you start looking at different scenarios.
I drew it just to be convinced,
its a good learning curve,
BTW, Im rubbish at stuff I cant touch, thats why I dont do lap dancing clubs,,,,,,,
I drew it just to be convinced,
its a good learning curve,
BTW, Im rubbish at stuff I cant touch, thats why I dont do lap dancing clubs,,,,,,,
Hmmm, let me try beginners luck again!! [i must be mad!!] You isolated the house at the CU. This is a DP switch/disconnector, that presumably worked. You said you did not do a "proper" deadness [for want of a better word] check, but everything went off.
Now then, it appears that the CPC was still live.......Hmmmm..... well.... if the CPC is live, then the earth bar in the CU must be live too. The earth bar is connected to the MET, so that must have been live too, and that is connected to the neutral [as it is pme]
Sooooo, how is it live???
Either the earthing conductor was not [conducting that is!!] and the MET was bonded to an incoming service that was live some how,
or,
The MET was not bonded to "earthy" incoming services, [all plastic in a newish house] and the neutral that the MET is connected to ij the cutout [cos its pme] was not as "neutral" as one would like!!
Soooooo, something wrong with the incoming PME but the house holder did not notice as, well, he would not if all the metalwork was bonded to the MET as it would all be the same potential. [unless he went out side with his ancient class one black and decker!!]
All i can think of!!
Do not all laugh at once!!!!!!!!!!!!!!!!
john
Now then, it appears that the CPC was still live.......Hmmmm..... well.... if the CPC is live, then the earth bar in the CU must be live too. The earth bar is connected to the MET, so that must have been live too, and that is connected to the neutral [as it is pme]
Sooooo, how is it live???
Either the earthing conductor was not [conducting that is!!] and the MET was bonded to an incoming service that was live some how,
or,
The MET was not bonded to "earthy" incoming services, [all plastic in a newish house] and the neutral that the MET is connected to ij the cutout [cos its pme] was not as "neutral" as one would like!!
Soooooo, something wrong with the incoming PME but the house holder did not notice as, well, he would not if all the metalwork was bonded to the MET as it would all be the same potential. [unless he went out side with his ancient class one black and decker!!]
All i can think of!!
Do not all laugh at once!!!!!!!!!!!!!!!!
john
I was thinking reversed polarity on the 'ring final' with the neutral for the landing light taken off the sockets - connecting the strapper to the cpc in the three core would then give a path back to the supply neutral - but it doesn't explain how anything is 'live' if the main switch is open. :C
nothing to be laffed at John,
its got you thinking,
Im not even going to say its one of the limitations of why I regard PME(in this country) as defective, as we have already seen, TT has its limitations too.
- Joined
- Nov 28, 2009
- Messages
- 14,762
- Reaction score
- 951
No, CPC was not live, well and truly at earth potential direct from the PME head.
I think some of you have got it, but I won't spill the beans just yet, in case a few more want to have a go, but I will post the answer later on tonight.
I'm beginning to think along those lines, Steps, because if the 'main switch' isn't faulty, or by-passed, then the only 'potential' that could exist is on the MET via the PME supply - but then you still need to complete the circuit.
- Joined
- Nov 28, 2009
- Messages
- 14,762
- Reaction score
- 951
Actually this fault has nothing to do with PME and in this case the PME supply was not defective.
Had this same fault occurred however on a TT installation, then when I started to cut the cable, my lead lamp would probably only have glowed dimly.
CPC at 0 volts relative to what??
- Joined
- Nov 28, 2009
- Messages
- 14,762
- Reaction score
- 951
CPC is correctly bonded to neutral at the PME supply head, and bonded to water / gas as it should be, so it's 0V relative to what it should be. The fault did not relate in any way to a defective supply or defective earthing.
cm304eex
Well-known member
Ok you got me:C:
Probably wrong but is there a seperate board in the property( just a stab in the dark?)
Probably wrong but is there a seperate board in the property( just a stab in the dark?)
Manator
©Honorary Essex Boy™
No its all on the same board, new wiring and not that old
No extra funny feeds from solar panels??
- Joined
- Nov 28, 2009
- Messages
- 14,762
- Reaction score
- 951
No.
One PME supply. No other sources. Just the one CU in the house. No external influences.
Manator
©Honorary Essex Boy™
This whilst not being a common fault can be found very easily, there are no other feeds, and the polarity feeding the CU is correct. Remember this is a 16th edition board with some circuits fed direct from the main switch and some VIA the main switch to a RCD unit.
The main DP switch was off, but the MCB's were still on, so one of the circuits protected by one of the MCB's must have had a feed from somewhere....... where though....
