odd voltages

[socalelect]

hopefully someone can help me anwser theses questions last week i installed a new subpanel in the shop for lighting and some addl. 120v outlets the panel is 240 volt single phase 200 amp 4 wire feed to it isolated ground and neutral . after i juiced it up i was checking voltages in the panel as i always do but what i got perplexed me a bit

L1 to N 115
L1 to G 116.5
L2 to N 118
L2 to G 120
L1 to L2 233
N to G varies between 1.5 and 4.5 volts

why are my line voltages to ground higher than line to neutral and i dont belive i should show any voltage from N to G ? correct ?

 

[glene77is]

L1 to N 115
L1 to G 116.5
L2 to N 118
L2 to G 120
L1 to L2 233
N to G varies between 1.5 and 4.5 volts

SocalElect,
Welcome to the forums.
Interesting post.

(1) Try placing a good load on each leg, then read voltages.
(2) Check your sub-panel service neutral connections, carefully.
(3) You have provided a GEC, if needed, right ? (just for lightning)

I am interested in the results of this post, :happyyes:
but I have just started lecturing at a college, four electronic courses,
so will check back when I can. Am busier than I want to be. :bye:

 

[Dennis Alwon]

I would almost suspect something in the transformer causing those voltages. It is curious as to why the voltage to ground is higher than voltage to neutral. Voltage from the neutral to ground should be at 0 or close to it. I would also use an ampmeter to see what the amps are on the egc. There must be something using the ground as a return path.

I would also turn the breaker off to the sub panel and take readings back at the service disconnect. In fact start by shutting everything done and see what happens on the line side.

 

[cadpoint]

Give us some more details, please.

Was it run in the air, or what type of conduit, what type of wire used, was it a bare grounded wire?

With all the lack usuall weather, I'm sure a lot of funny things are starting to happen with all the underground services. I'll defer to Dennis's statement. (Why did I think you where in TX)?

What's the reading at the main panel on the main breaker?

It's been said here before where many out of the box panels are loose and sometimes even broken, just a thought!

Welcome aboard.

 

[don_resqcapt19]

There will normally be a voltage from the neutral to ground at a subpanel .... you are measuring the voltage drop on the neutral. The only place that the neutral to ground voltage is zero is at the location of the main bonding jumper.

 

[Dennis Alwon]

There will normally be a voltage from the neutral to ground at a subpanel .... you are measuring the voltage drop on the neutral. The only place that the neutral to ground voltage is zero is at the location of the main bonding jumper.

But isn't 4 volts rather high?

 

[ronaldrc]

I agree with Don that is nothing but voltage drop on the neutral.
And as Don said there is load on the ground so the voltage would read higher.

I have worked on services that would produce a arc if you jumpered the
neutral to the ground buss.

 

[hurk27]

this sounds like at the time of mesurments you have loads switching on and off and the readings are not compairable, to compaire voltages you have to have a constant load on both legs at or ahead of the test point all the way to the service,

Having 115v L1-N and 118v L2-N which = the 233v line to line makes sense if we assume there is not enough neutral current to create a voltage drop in the neutral at this sub-panel, but with the 116.5v L1-G and 120v L2-G starts to sound like you have somthing at or ahead of the sub-panel that is using a EGC for return current and it is between L1 and the EGC, I would put a amp probe around all hots and the neutral feeding this sub and see if anything is using the EGC for a return, if you show any amps then find the path by turning off each circuit one at a time, also do a voltage compairision between the main service panel and this sub.

Something is using a EGC after the MBJ?

 

[hurk27]

Sitting here trying to put some math to this, and the differance between the L1-L2-G = 236.5 and L1-L2-N = 233 which should show a 3.5 volt drop in the neutral, and a 3 volt drop on L1 which would equal 239.5 at the main service (233 + 6.5) but something doesn't sound right in the way I'm figuring this, as any voltage drop between one leg and the neutral will raise the voltage on the other leg perportionally? so it should show a 2 volt drop on the neutral with a 1 volt drop on L2 and a 1.5 volt drop on L1, undersize neutral?

 

[socalelect]

cadpoint , heres a little info on how its ran it starts as a overhead drop from the poco to the 400 amp main panel ( neutral ground bond here )
1 driven rod then makes a 200 foot rununder ground sch40 pvc to another building subpanel ( no neutral bond here ) only load here is a few lights and a air compressor then makes a 200 amp 250 foot run underground sch40 pvc to the main shop to a subpanel in there with 1 driven rod, then it branches off to a few panels including the one i just added , its about 50 feet from the 1st panel in the shop 4 wire feed in EMT

all underground feeds are 4 wire
all conductors are sized approitaly
now heres the kicker , i started troubleshooting today started in the newest panel in the shop and the voltages are all normal
and no voltage between ground and neutral and equal voltages line to neutral and line to ground , the only tthing that has changed is it rained a bunch yesterday afternoon and night

 

[Little Bill]

cadpoint , heres a little info on how its ran it starts as a overhead drop from the poco to the 400 amp main panel ( neutral ground bond here )
1 driven rod then makes a 200 foot rununder ground sch40 pvc to another building subpanel ( no neutral bond here ) only load here is a few lights and a air compressor then makes a 200 amp 250 foot run underground sch40 pvc to the main shop to a subpanel in there with 1 driven rod, then it branches off to a few panels including the one i just added , its about 50 feet from the 1st panel in the shop 4 wire feed in EMT

all underground feeds are 4 wire
all conductors are sized approitaly
now heres the kicker , i started troubleshooting today started in the newest panel in the shop and the voltages are all normal
and no voltage between ground and neutral and equal voltages line to neutral and line to ground , the only tthing that has changed is it rained a bunch yesterday afternoon and night

The rain could definitely have some effect on your readings. But with the added info you gave on all the other sub panels that you have, I would bet you had some loads on during your initial readings that were not on during your most recent readings. However, you still might have something using the EGC as a return path. If you find these readings off (from normal) again, I would start at the main panel and work your way back to the newest sub panel and see where your change starts.

 

[kwired]

cadpoint , heres a little info on how its ran it starts as a overhead drop from the poco to the 400 amp main panel ( neutral ground bond here )
1 driven rod then makes a 200 foot rununder ground sch40 pvc to another building subpanel ( no neutral bond here ) only load here is a few lights and a air compressor then makes a 200 amp 250 foot run underground sch40 pvc to the main shop to a subpanel in there with 1 driven rod, then it branches off to a few panels including the one i just added , its about 50 feet from the 1st panel in the shop 4 wire feed in EMT

all underground feeds are 4 wire
all conductors are sized approitaly
now heres the kicker , i started troubleshooting today started in the newest panel in the shop and the voltages are all normal
and no voltage between ground and neutral and equal voltages line to neutral and line to ground , the only tthing that has changed is it rained a bunch yesterday afternoon and night

Were the same loads operating the second time? Less neutral load = less voltage drop. Try loading one line to neutral fairly heavily and I bet your neutral to ground voltage is even higher. This is likely normal voltage drop on the neutral conductor that you are measuring. It is one reason why once you are past the service equipment you are supposed to separate the neutral from the equipment grounding conductor otherwise you are subjecting this same voltage drop to the EGC and it will be measurable from the EGC to earth and also creating a shock hazard.

 

[weressl]

There will normally be a voltage from the neutral to ground at a subpanel .... you are measuring the voltage drop on the neutral. The only place that the neutral to ground voltage is zero is at the location of the main bonding jumper.

In addition there is a capacitive and inductive voltage charge between the ground and phase wires that is additive to the neutral voltage drop.