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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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10th Oct 2017, 9:56 pm | #41 | |
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
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Re: European Black/Blue Mains Lead
Quote:
Chris
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10th Oct 2017, 10:16 pm | #42 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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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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10th Oct 2017, 10:31 pm | #43 |
Pentode
Join Date: Oct 2017
Location: Newton-le-Willows, Merseyside, UK.
Posts: 158
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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. |
11th Oct 2017, 11:48 am | #44 | |
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
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Re: European Black/Blue Mains Lead
Quote:
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. Chris
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