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Old 14.10.2011, 14:29
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Re: Question about installing ceiling lights

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I'm gonna make a fool of myself here, I know it...

But then doesn't the electricity stuff run through the lightbulb, into the neutral wire, into the earth wire and then make the light fitting live?
No, it's grounded.

Tom
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Old 14.10.2011, 15:28
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Re: Question about installing ceiling lights

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In Germany the neutral & earth would be wired together, I thought the concept most dangerous however an electrician here did not bat an eyelid when I mentioned it. His response was that neutral is grounded at the generating station.
The generator neutral point is indeed earthed through a resistance at the power station. The three-phase electrical energy is then transmitted via three conductors to the final distribution transformer. The transformer has a neutral connection and this is also earthed.

This is why you only see power lines with a multiple of 3 conductors (3 or 6); you are standing on the neutral conductor - it is the earth. (Incidentally, the power lines that have a multiple of two conductors (2, 4, etc) belong to SBB as they have their own network runing at 16.667 Hz - this is why Switzerland is a rat's nest of power transmission lines as there are two fully independant networks; most other countries use the normal 50Hz network)

Anyway, the neutral (earthed at the transformer) conductor is now back with us, and you now have a live and neutral coming into your house. The earth conductor at the point of entry is simply bonded to the neutral conductor (search online for "PME system"). On it's way to your house, the neutral conductor in the cable is earthed at regular intervals.

But, connecting the neutral and earth together at a light fitting? That would just trip the main RCD in your house, which trips when the current flowing into the light fitting (through the live) does not match the current flowing out through the neutral. Usually, this means the current is flowing, not only back via the neutral cable, but is also taking an additional scenic route, which is usually your body. In this case, however, the scenic route is the earth conductor, which is now being used for something it shouldn't

The earth cable has only one single function - to protect. It should only ever be used for that purpose!
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  #23  
Old 14.10.2011, 15:57
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Re: Question about installing ceiling lights

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The generator neutral point is indeed earthed through a resistance at the power station. The three-phase electrical energy is then transmitted via three conductors to the final distribution transformer. The transformer has a neutral connection and this is also earthed.

This is why you only see power lines with a multiple of 3 conductors (3 or 6); you are standing on the neutral conductor - it is the earth. (Incidentally, the power lines that have a multiple of two conductors (2, 4, etc) belong to SBB as they have their own network runing at 16.667 Hz - this is why Switzerland is a rat's nest of power transmission lines as there are two fully independant networks; most other countries use the normal 50Hz network)

Anyway, the neutral (earthed at the transformer) conductor is now back with us, and you now have a live and neutral coming into your house. The earth conductor at the point of entry is simply bonded to the neutral conductor (search online for "PME system"). On it's way to your house, the neutral conductor in the cable is earthed at regular intervals.

But, connecting the neutral and earth together at a light fitting? That would just trip the main RCD in your house, which trips when the current flowing into the light fitting (through the live) does not match the current flowing out through the neutral. Usually, this means the current is flowing, not only back via the neutral cable, but is also taking an additional scenic route, which is usually your body. In this case, however, the scenic route is the earth conductor, which is now being used for something it shouldn't

The earth cable has only one single function - to protect. It should only ever be used for that purpose!
i don't know if the suggestion was to wire the casing of the lamp fitting to the neutral wire in the event that there is no separate earth wire?
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Old 14.10.2011, 16:16
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Re: Question about installing ceiling lights

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i don't know if the suggestion was to wire the casing of the lamp fitting to the neutral wire in the event that there is no separate earth wire?
Best to leave it floating then.

Tom
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Old 14.10.2011, 16:36
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Re: Question about installing ceiling lights

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i don't know if the suggestion was to wire the casing of the lamp fitting to the neutral wire in the event that there is no separate earth wire?
The places I have seen the earth & neutral tied were in old houses without RCD's.
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