IET Forums - Neutral voltage question

IET

search : help : home

Latest News: Private messages, your photo, profiles, email notifications

Categories:

latest topics : statistics

IET » Wiring and the regulations » Neutral voltage question

Topic Title: Neutral voltage question
Topic Summary:
Created On: 28 March 2019 02:22 PM
Status: Read Only

Linear : Threading : Single : Branch

Search Topic

Topic Tools

	View similar topics
	Print this topic.

28 March 2019 02:22 PM
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
Top : Bottom

28 March 2019 02:33 PM
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
Top : Bottom

28 March 2019 02:36 PM
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 de-avatared
Top : Bottom

28 March 2019 02:38 PM
Legh Posts: 4427 Joined: 17 December 2004	Apologies Mike for cross- threading your post ..... Is the ship about to sink? Legh ------------------------- http://www.leghrichardson.co.uk de-avatared
Top : Bottom

28 March 2019 02:46 PM
mapj1 Posts: 12039 Joined: 22 July 2004	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
Top : Bottom

28 March 2019 02:49 PM
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.
Top : Bottom

28 March 2019 03:08 PM
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
Top : Bottom

28 March 2019 04:36 PM
Legh Posts: 4427 Joined: 17 December 2004	Sink me ! .......... I suppose it wIll become a block ship .... Legh ------------------------- http://www.leghrichardson.co.uk de-avatared
Top : Bottom

28 March 2019 10:34 PM
MHRestorations Posts: 83 Joined: 22 October 2017	I seriously need to redirect this forum to the new one in my router or bookmarks. I can never find it
Top : Bottom

28 March 2019 10:42 PM
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.
Top : Bottom

29 March 2019 01:45 PM
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.
Top : Bottom