amperage on a neutural
- Thread starter SPARKYNSJ
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chris kennedy
Senior Member
- Location
- Miami Fla.
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- 60 yr old tool twisting electrician
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Actually fed from two legs of 120/208 3-phase?
brian john
Senior Member
- Location
- Leesburg, VA
Sounds logical and mathematical to me!
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
Could this be some of a neighbors neutral current ?
Either:
Turn off the main and see if it all goes away.
Or
Measure current on the GEC in the panel.
Either:
Turn off the main and see if it all goes away.
Or
Measure current on the GEC in the panel.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
If the panel is fed with 2 phases of a 3-phase wye, then the neutral should be about 33, not 26. So the amps don't add up for either services.
Did you check the GEC for amperage?
Did you check the GEC for amperage?
erickench
Senior Member
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- Brooklyn, NY
This makes alot of sense.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
Why Eric, does that make so much sense?
But knowing how much of the ungrounded current is L-N and how it is divided between the legs will help in knowing what the neutral load should be and then start looking from there.
Roger
gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
091205-0851 EST
SPARKYNSJ:
Additional information is needed.
We really need to know if source is single or three phase. Measure each line to neutral voltage with a DVM that resolves 0.1 V. Then measure the line to line voltage with the same meter. If the sum of the two voltages from line to neutral are close to equal to the line to line voltage, then it is a single phase center tapped transformer supply. If the sum of the two line to neutral voltages is closer to the line to line voltage divided by 0.866, then it is a 3 phase Y source.
Next remove all loads from the main panel. Measure the current from the ground bus of the main panel to all grounding paths. Most particularly the water pipe. If there is negligible current, then the neutral current is a result of loads on the main panel.
If the supply is three phase, both line to neutral voltages are very close in value (like within 1 V), and all loads are resistive, then assuming 120 deg phase difference the neutral current is about 38 - 0.5*21 = 38 - 10.5 = 27.5 A. Not too far from the 26 A measured.
Separately assume it is really single phase, then an adequate reactive load can cause the same result.
.
SPARKYNSJ:
Additional information is needed.
We really need to know if source is single or three phase. Measure each line to neutral voltage with a DVM that resolves 0.1 V. Then measure the line to line voltage with the same meter. If the sum of the two voltages from line to neutral are close to equal to the line to line voltage, then it is a single phase center tapped transformer supply. If the sum of the two line to neutral voltages is closer to the line to line voltage divided by 0.866, then it is a 3 phase Y source.
Next remove all loads from the main panel. Measure the current from the ground bus of the main panel to all grounding paths. Most particularly the water pipe. If there is negligible current, then the neutral current is a result of loads on the main panel.
If the supply is three phase, both line to neutral voltages are very close in value (like within 1 V), and all loads are resistive, then assuming 120 deg phase difference the neutral current is about 38 - 0.5*21 = 38 - 10.5 = 27.5 A. Not too far from the 26 A measured.
Separately assume it is really single phase, then an adequate reactive load can cause the same result.
.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
On single-phase distribution, shouldn't the neutral always be A-B=N (use absolute value)? I don't see how L-N loads affect this since when they(branch circuit neutrals) all hit the busbar, the service entry N amps would be the difference in the two ungrounded conductors.
Exactly, and when we find out how much of the current is L-L in the ungrounded conductors we can then figure out how much current "should" be L-N, then we would need to figure out how these L-N loads are divided between the legs and this would let us know how much current we "should" be reading on the service neutral.
If the OP hadn't said 120/240 v I would think the three phase scenario would be the answer as already stated.
Roger
Last edited:
gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
091205-0953 EST
hardworkingstiff:
Your statement is correct for resistive loads in the center tapped supply circuit you are assuming.
When you make an ordinary current measurement there is no phase information. Thus, if one current is shifted in phase relative to the other there will be a different result than that of your equation.
In fact your equation with the minus sign and using the absolute values of the currents implies that the two currents flowing into the neutral are 180 deg out of phase.
.
hardworkingstiff:
Your statement is correct for resistive loads in the center tapped supply circuit you are assuming.
When you make an ordinary current measurement there is no phase information. Thus, if one current is shifted in phase relative to the other there will be a different result than that of your equation.
In fact your equation with the minus sign and using the absolute values of the currents implies that the two currents flowing into the neutral are 180 deg out of phase.
.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
That (IMO) is the determing factor in a "single-phase" distribution. I've read the many pages on the discussion of whether 2 legs and a neutral of a WYE is a single-phase distribution, and I still maintain this view.
How much phase shifting would you expect to see in a residence? I thought that's what the OP suggested, maybe I missed that.
EDIT: I went to the OP, and it did not mention a residence, so my simplistic review is..... worthless,
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
091205-1026 EST
dkarst:
If I did it on paper I might get it correct. I only subtracted the inphase component. 33 does seem to be the approximate value assuming resistive loads from neutral to the lines.
.
dkarst:
If I did it on paper I might get it correct. I only subtracted the inphase component. 33 does seem to be the approximate value assuming resistive loads from neutral to the lines.
.
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