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Topic Title: Neutral voltage question
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Created On: 28 March 2019 02:22 PM
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 28 March 2019 02:22 PM
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FiftyHertz

Posts: 28
Joined: 13 April 2018

Hi all,

Hoping someone can help with this, as it bothering me that I dont know this.

This is quite tricky to explain without an image. Essentially, if we have a circuit supplying one luminaire. The line conductor has a voltage of 230v from earth potential supplying the light. To complete the circuit, on the return leg a neutral is required (<50v from earth potential). Where is the point where the neutral is no longer at mains voltage, is it at the neural terminals?

Is it a case of the luminaire will "use up" the supplied mains voltage?

Any assistance is appreciated.

Thanks
 28 March 2019 02:33 PM
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mapj1

Posts: 12039
Joined: 22 July 2004

Forum closing soon, so if we get pushed off, please start again in the new place, same title.

OK, so the voltage between L and N is 240V or whatever at the substation, and so long as current is flowing, then as we walk along the wires towards the load, voltage is dropped, I * R but R in the wires is very small - we make the wires big enough this is alwys true. As voltage is dropped in the live, the voltage is falling as we move from the source and is nearest earth towards the load end, even if that is only a volt or two lost out of 230.
The current in the neutral is flowing the other way, so the voltage drop is upwards - rising a volt or two nearer towards the live at the load end. The load sees a difference relative to the origin, due to both Live and Neutral voltage drops.

(the exact voltage may be complicated as the 0v refernce, the N-E bond, may not be at the substation, but the slope is always that way, but some voltages may be below zero as it were - i.e. the phase of the sine wave is inverted.)
Hopefully most of the voltage is dropped in the load; and if you could cut the load in half and stick a meter half way along - and with an old fashioned bar type electric heater maybe you could, that point would be equally far from the original L and N, and so at 120 V to earth or so.

-------------------------
regards Mike
 28 March 2019 02:36 PM
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Legh

Posts: 4427
Joined: 17 December 2004

May i suggest that you switch this post over to the 'new' electrical forum as this one is about to sink below the waves
Three phase voltage unbalanced might be a start. and is likely to be covered in greater depth elsewhere.

Legh

-------------------------

http://www.leghrichardson.co.uk

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 28 March 2019 02:38 PM
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Legh

Posts: 4427
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Apologies Mike for cross- threading your post ..... Is the ship about to sink?

Legh

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http://www.leghrichardson.co.uk

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 28 March 2019 02:46 PM
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mapj1

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Who knows - but FiftyH, like farmboy, has not popped up in the lifeboat on the other side yet - I thought I'd leave 3ph out of it and do a single phase example first.

-------------------------
regards Mike
 28 March 2019 02:49 PM
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broadgage

Posts: 3170
Joined: 07 August 2007

Originally posted by: Legh

Apologies Mike for cross- threading your post ..... Is the ship about to sink?



Legh


About to be deliberately scuttled I think as the vessel is obsolete and the replacement has already been launched.
 28 March 2019 03:08 PM
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FiftyHertz

Posts: 28
Joined: 13 April 2018

Apologies, i will move this over to the new forum.

Thanks for the post Mike, hopefully we can continue on the over side

Cheers
 28 March 2019 04:36 PM
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Legh

Posts: 4427
Joined: 17 December 2004

Sink me ! .......... I suppose it wIll become a block ship ....

Legh

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http://www.leghrichardson.co.uk

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 28 March 2019 10:34 PM
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MHRestorations

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I seriously need to redirect this forum to the new one in my router or bookmarks. I can never find it
 28 March 2019 10:42 PM
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potential

Posts: 1774
Joined: 01 February 2007

Originally posted by: FiftyHertz

Hi all,
Hoping someone can help with this, as it bothering me that I dont know this.
This is quite tricky to explain without an image. Essentially, if we have a circuit supplying one luminaire. The line conductor has a voltage of 230v from earth potential supplying the light. To complete the circuit, on the return leg a neutral is required (<50v from earth potential). Where is the point where the neutral is no longer at mains voltage, is it at the neural terminals?
Is it a case of the luminaire will "use up" the supplied mains voltage?
Any assistance is appreciated.
Thanks

In comparison to the wiring, which has a very low impedance, the luminaire is a high impedance.
Consequently nearly all the supply voltage will be present at the luminaire.
 29 March 2019 01:45 PM
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potential

Posts: 1774
Joined: 01 February 2007

This is a test to see if the forum is closed.

Odd.
Only a few minutes ago the forum had a heading claiming no replies or new posts could be made.
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