What would this be?

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Pierre C Belarge

Pierre C Belarge

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Westchester County, New York
A person takes a test measurement with a voltage tester at the panel installed 118 ft from its source. The conductors are 4 AWG, with an actual load of around 16-19 amps. A 240 volt load to a pool pump is the largest load on that panel.
One of the test leads is connected to the grounded conductor/bus (4 AWG), the other test lead is connected to the equipment grounding conductor (8 AWG).
The resultant reading on the tester is 5volts.

What has the person just tested for?

Is this reading acceptable?
 
Pierre C Belarge said:
A person takes a test measurement with a voltage tester at the panel installed 118 ft from its source. The conductors are 4 AWG, with an actual load of around 16-19 amps. A 240 volt load to a pool pump is the largest load on that panel.
One of the test leads is connected to the grounded conductor/bus (4 AWG), the other test lead is connected to the equipment grounding conductor (8 AWG).
The resultant reading on the tester is 5volts.

What has the person just tested for?
Click to expand...

Voltage drop on the neutral

I have to assume there are 120 volt loads and they are causing voltage drop on the grounded conductor.

Is this reading acceptable?
Click to expand...


Sounds like a design issue and the answer would depend on the nature of the load served. :smile:
 
iwire said:
Voltage drop on the neutral
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Or alternately 'voltage drop on the ground' - depending on how you look at it....

One can safely assume that the grounded and the grounding conductors are different sizes as allowed - the grounding would be smaller and therefore have a higher voltage drop than the grounded.... Say a conduit coupled with the grounding may be better - but who knows....

Pierre C Belarge said:
What has the person just tested for?

Is this reading acceptable?
Click to expand...
You might have to ask them.... And yeah - sure it's acceptable - we have no idea what is on the neutral as a load, which could accomadate for much of it. Try testing with no load, and then a high but very well balanced load and see what you get then.....
 
Pierre C Belarge said:
A person takes a test measurement with a voltage tester at the panel installed 118 ft from its source. The conductors are 4 AWG, with an actual load of around 16-19 amps. A 240 volt load to a pool pump is the largest load on that panel.
One of the test leads is connected to the grounded conductor/bus (4 AWG), the other test lead is connected to the equipment grounding conductor (8 AWG).
The resultant reading on the tester is 5volts.

What has the person just tested for?

Is this reading acceptable?
Click to expand...
See article 215.2(A)(3) fpn no2.You tested for voltage drop on the neutral feeder. Seems high for that small load. Check the same at the main service disconnect. Sounds like you might have a neutral/ground event occuring. Also check the leads on the tester before all readings.
 
e57 said:
the grounding would be smaller and therefore have a higher voltage drop than the grounded.
Click to expand...

Not true in this case. Since the actual load is 16-19 amps the conductors could have been #12 or #10 in which case the upsizing of the feeder conductors would be proportional to the egc.
 
IMHO 5V is way too high a voltage for neutral to ground voltage in the described circumstances.

Assume for a moment that the stated 19A was not a combination of 240V and 120V loads, but instead was pure unbalanced 120V load, putting 19A on the neutral.

The neutral conductor is a #4, and let's assume that it is aluminium. This gets us to about 0.4 ohms per 1000 feet. We get 19 * 0.4 * 0.118 = 0.9 Since the current on the neutral is supposedly lower than 19A, the voltage measured should be even lower.

I would not call 5V a design issue; I would call it unexpectedly high and cause to look for a connection problem.

-Jon
 
Pierre C Belarge said:
One of the test leads is connected to the grounded conductor/bus (4 AWG), the other test lead is connected to the equipment grounding conductor (8 AWG).
The resultant reading on the tester is 5volts.
Click to expand...
Try the same experiment with no loads and with various loads.
 
LarryFine said:
Why would the EGC have any voltage drop? :-?
Click to expand...

Given the length quoted, I would have guessed that we are talking about a detached structure. If so, there would be a grounding electrode connected to the EGC. Earth currents could be coupled into one grounding electrode system and out of the one at the other structure. Just a possibility, but IMHO not likely.

-Jon
 
quogueelectric said:
If there is current on it there will be voltage drop. Oh no here we go again. Real life VS desk theory.
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Of course I understand how and why it could occur. I should have said "why should there be ..."
 
I am actually gathering information about this installation from you guys...kind of like getting your ideas.


I was called into a job 2 days ago by an EC, who is asking for my help. I do not want to go over the particulars, I believe this job is going to become very "dicey" so I want to blur the job details.

I had the EC take some measurements at the site.

I did not do the math, but I believe the VD is not too excessive for the situation I described above.
 
Pierre C Belarge said:
I am actually gathering information about this installation from you guys...kind of like getting your ideas.


I was called into a job 2 days ago by an EC, who is asking for my help. I do not want to go over the particulars, I believe this job is going to become very "dicey" so I want to blur the job details.

I had the EC take some measurements at the site.

I did not do the math, but I believe the VD is not too excessive for the situation I described above.
Click to expand...
If you read the code article I gave you you will see that there Is already enough VD on 1 leg to hang a V on the inspection. You have to take into consideration the VD on the other 2 conductors also with a marginal load on a pool panel I presume. It takes 2 to tango There is a problem somewhere but too many unknowns to troubleshoot from the desk. Only 120 ft of #4 has almost a 5% vd on only 1 leg. You have to consider the other #4 at 120 feet bringing it back for total VD. You already know there is a problem or you wouldnt be asking about it.
 
e57 said:
Or alternately 'voltage drop on the ground' - depending on how you look at it.........
Click to expand...

IMO that is reaching.

winnie said:
Given the length quoted, I would have guessed that we are talking about a detached structure. If so, there would be a grounding electrode connected to the EGC. Earth currents could be coupled into one grounding electrode system and out of the one at the other structure. Just a possibility, but IMHO not likely.
Click to expand...

I agree, possible but not likely, 'Myth Busted ;)
 
quogueelectric said:
I know you understand I should have worded that better. Sounds like a Midwest pool panel to me.
Click to expand...


So I have to ask, Why would you assume it's 'Midwest pool panel' and why would you assume enough current on the EGC to cause 5 volts of drop? :-?
 
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