question about neutral voltage

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steveng

Senior Member
Location
Texas
i have a receptacle circuit 120 v, when i read hot to neutral i get 120v,
when i read neutral to ground i get 5 volts.

where is the 5 volts coming from? is this common?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
steveng said:
i have a receptacle circuit 120 v, when i read hot to neutral i get 120v,
when i read neutral to ground i get 5 volts.

where is the 5 volts coming from? is this common?
First test: what happens if you turn off or disconnect every load from this circuit?
 

haskindm

Senior Member
Location
Maryland
The neutral conductor is a current carrying conductor and since it carries current and has resistance you will experience votage drop. The grounding conductor does not carry current (unless it is clearing a fault) and so it will NOT have voltage drop. You are comparing a conductor with voltage drop to a conductor that has no voltage drop, so you are actually reading the voltage drop. Five volts is a little on the high side, but not totally unreasonable for a fairly heavily loaded circuit. If this is a lightly loaded circuit, it may indicate a poor connection somewhere in the circuit. If this is the case, the first thing to check would be the receptacles. Make sure the connections are tight, especially if the receptacles are the type where the wire just sticks in the back and is held by a spring clamp.
 

dinkelja

Member
That's a good point haskindm, however the initial post lead me to believe that a voltage reading is being taken between neutral and ground on the receptacle. Steveng, can you confirm?
 

rattus

Senior Member
Maybe?

Maybe?

steveng said:
i have a receptacle circuit 120 v, when i read hot to neutral i get 120v,
when i read neutral to ground i get 5 volts.

where is the 5 volts coming from? is this common?

Perhaps you have a current in the EGC? Maybe a miswired receptacle somewire along that branch circuit? Sometimes the EGC is purposely used as a current carrying conductor--not good.
 

haskindm

Senior Member
Location
Maryland
I understand that the OP is testing from neutral to ground. There will be a difference of potential in almost any circuit that you test in this manner that has a load on it. The neutral (grounded) conductor will experience voltage drop, while the grounding conductor does not. There will be a small potential difference between these two conductors. It is not unusual, it is normal and expected. It should not amount to more than a few volts. Mike has written several articles on this subject. The less load that you have on the neutral (as in a balanced multiwire circuit) the less voltage difference will be detected. I have noticed this most dramaticaly in circuits fed from sub-panels where the feeder neutral was carrying a good amount of neutral current.
 

steveng

Senior Member
Location
Texas
yes, i am referring to the neutral to egc.

this is a mwbc serving loads in a fitness center room with multiple exercise
machines, ie , treadmills.

i thought 5 volts was high, thats why i am asking. thanks for the explanations
its clearer now.:grin:
 

brian john

Senior Member
Location
Leesburg, VA
5 volts being high would depend on job specs for allowable voltage drop, this is about 4.15% in a 120 VAC circuit.


Measure the neutral current at the panel and measure the phase to neutral voltage at the panel and at the far end of the circuit with loads on.

VD.jpg



This was an old table from a VD report I had to do did not calculate for 5% VD
 
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don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Brian,
5 volts being high would depend on job specs for allowable voltage drop, this is about 4.15% in a 120 VAC circuit.
Actually the voltage drop on the circuit would be higher than 4.15% as this is only the voltage drop on the grounded conductor...there will be additional drop on the ungrounded conductor.
Don
 

brian john

Senior Member
Location
Leesburg, VA
Don

True, I forgot to include the one thing that allows voltage drop a complete circuit....

In addition it was mentioned this is a multi-wire branch circuit, that means either the loading of the branch circuit is not balanced or there is high harmonic* content loads, if the 5 VAC VD is an issue try reconnecting loads to achieve a balanced loading.


*With newer gym equipment I would lean towards harmonics contributing to the neutral current, just a guess.
 
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brian john

Senior Member
Location
Leesburg, VA
I would think not, unless a piece of equipment fails for any reason then the manufacture is all over it.

I had a report sometime ago (I am terrible at filing these things) were some firm did a test and had 15-25 VAC* between neutral to ground and electronic equipment purred along with no issues.

* I cannot remember what the maximum voltage imposed on the circuit was, nor what types of equipment I know one was a PC.
 
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