# Maximum potential between neutral and ground



## mshields (Sep 20, 2011)

I have been tasked with finding somewhere in the IEEE standards a requirement for maximum permissible potential between neutral and ground on a 120V circuit.

I've never seen such a thing and am not even sure where to look?

Any thoughts/idea's?

Thanks,

Mike


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## ICE (Sep 20, 2011)

You might get an answer here:

http://www.electriciantalk.com/


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## cda (Sep 21, 2011)

M.  And the answer is::::


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## peach (Sep 21, 2011)

I believe the potential needs to be zero


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## jar546 (Sep 22, 2011)

Not sure I know exactly what you are looking for.  Can you please show us the exact wording of the question.

At the main disconnect, the neutral and equipment ground are bonded together.  Beyond that, the equipment ground and neutral continue to the grounding electrode system and the resistance to earth of that system in relationship to the POCO transformer will always vary based on distance, soil conditions, etc.  This will only come into effect with a loss of neutral.  If our grounds had the same resistance to the POCO transformer as the neutral, then when a home lost a neutral, it would not be immediately noticed as the ground would pick up the load depending on where the neutral was lost such as at the meter base in a typical home installation.  Most losses of neutral at the meter base are immediately recognized and create problems since the resistance of the GES to the POCO transformer though the soil is rarely if ever 0 ohms.

Of course your question may be related to voltage drop so please clarify.

Great question.


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## Frank (Sep 22, 2011)

At which location?  The panel, or the end of the circuit?

See 2008 NEC 210.19 and 215.2 for allowable voltage drops in circuits and feeders respectivly.

Half of the 3-5% voltage drop would occur in the line and half in the neutral.


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## chris kennedy (Sep 22, 2011)

ICE said:
			
		

> You might get an answer here:http://www.electriciantalk.com/





			
				jar546 said:
			
		

> Great question.


I also thought it is a great question and I did post it Tues evening over at ET. Link for interested parties.


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## raider1 (Sep 22, 2011)

peach said:
			
		

> I believe the potential needs to be zero


It is not possible to have 0 potential throughout the premise wiring system. At the load end of a circuit the potential difference will be dependent on the voltage drop between the grounded and equipment grounding conductors.



			
				Frank said:
			
		

> At which location?  The panel, or the end of the circuit?See 2008 NEC 210.19 and 215.2 for allowable voltage drops in circuits and feeders respectivly.
> 
> Half of the 3-5% voltage drop would occur in the line and half in the neutral.


Voltage drop is not enforceable because it is only mentioned in an informational note. (Other that 695.7 for fire pumps and 647.4(D) for sensitive electronic equipment)

Also the voltage drop we are talking about is not the branch circuit voltage drop but the voltage drop potential difference between the grounded conductor and the equipment grounding conductor.

Chris


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## ICE (Sep 22, 2011)

This might help:  http://www.mikeholt.com/strayVoltageVideo.php


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## Francis Vineyard (Sep 23, 2011)

mshields said:
			
		

> I've never seen such a thing and am not even sure where to look?Any thoughts/idea's?
> 
> Thanks,
> 
> Mike


An electrical engineer may have the answer; it could be IEEE Standard 142.

Seen where thermal imaging camera's are used for industrial inspection for poor connections by hot spots though I suppose it could work for 240/120v


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