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Old 10th Oct 2017, 9:56 pm   #41
cmjones01
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Default Re: European Black/Blue Mains Lead

Quote:
Originally Posted by Jon_G4MDC View Post
~2.5mm Blue/Black and plain copper earth?
Go to Norway, Clas Ohlson. It's what they have.

In any house of some age, blue and black might be swapped at any socket, the earth wire might be connected through or not. Fun.
Similar here in Poland. Older wiring tends to be blue/black or even black/black, and quite often neutral and earth are the same wire all the way to the socket. That's right, no separate circuit protective conductor. I can understand having 2-pin sockets with no earth, but having 3-pin sockets and pretending that the neutral is earth? No thank you!

Chris
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Old 10th Oct 2017, 10:16 pm   #42
julie_m
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Default Re: European Black/Blue Mains Lead

Surely it's the whole fact of the protective earth not ordinarily carrying any current that gives it its protective quality? If it was also carrying the return current from the appliance, then it -- and by extension, any exposed metalwork on the appliance -- could become live (via the impedance of the appliance; potentially a stalled motor, unmagmetised transformer, cold lamp filament or bridge rectifier and discharged electrolytic capacitor, if not a heating element of just a few tens of ohms -- in other words, not much current limiting) if the combined neutral / earth became disconnected between the consumer unit and the socket faceplate.

You would definitely need a 30mA sensitivity RCD with that sort of arrangement.
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Old 10th Oct 2017, 10:31 pm   #43
philthespark
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Default Re: European Black/Blue Mains Lead

Which is why in the UK we are not allowed to combine neutral and earth at an outlet, only at the service head, and then only on TNCS/ PME systems.
In the UK we normally only have 3 types of supply, TT, earth supplied via a rod driven into the ground. TNS, separate live neutral and earth from the distributors cable, and TNCS, the earth and neutral are combined in the service head and separate at that point.
Some foreign countries use one called CNE, combined neutral and earth, they use a 2 core cable to each point of use then effectively link the live and neutral in the back of the box.
The reason we bond all conductive surfaces to earth ( sink tops, pipework etc) is to prevent shocks by creating a sort of Faraday cage, if the earth in a house became live, then because all conductive surfaces were bonded to earth, they'd also be live, thus because you could not touch 2 surfaces at different potentials, you would not receive a shock, unless you used a metal cased appliance outside the premises, but it was connected inside.
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Old 11th Oct 2017, 11:48 am   #44
cmjones01
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Default Re: European Black/Blue Mains Lead

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Originally Posted by julie_m View Post
Surely it's the whole fact of the protective earth not ordinarily carrying any current that gives it its protective quality? If it was also carrying the return current from the appliance, then it -- and by extension, any exposed metalwork on the appliance -- could become live (via the impedance of the appliance; potentially a stalled motor, unmagmetised transformer, cold lamp filament or bridge rectifier and discharged electrolytic capacitor, if not a heating element of just a few tens of ohms -- in other words, not much current limiting) if the combined neutral / earth became disconnected between the consumer unit and the socket faceplate.
Yes, that's exactly the problem. I had a lucky escape at one point in a previous house which had this wiring arrangement. It turned out that the socket in the cellar which powered the washing machine was connected using fairly modern copper wires which were connected to older aluminium wires in a junction box. The connection was made by twisting the two dissimilar metals together and wrapping them in fabric tape. A recipe for metallurgical disaster? Yes, it was. Fortunately, when the washing machine stopped working one day, it was the junction in the live wire that had corroded away and melted the fabric tape, but the neutral was on its way too. If the neutral had failed first, the washing machine's metalwork would all have been at 220V - neutral and earth were commoned in the socket. Next to a sink, surrounded by damp washing. Fortunately I'm still here to tell the tale.

There was no RCD, but the whole house was powered from a 20A MCB in a box on the front wall of the house that used to trip at inopportune moments.

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