is this right or wrong?

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electricalperson

Senior Member
today i was doing a fire alarm system at a local hotel. the lady at the bar area called me over and asked me to look at her lights and plugs that didnt work. i took out my shiny new T+pro tester and stuck it in the receptacle and heres what i got.

L to N 119 volts

L to G 136 volts

N to G 45 volts

i called the "engineering" department and explained to them that they have a floating neutral and it should be fixed. (theres also receptacles in other parts of the buildings that dont work, not sure if its related or not and also a bunch of transformers for 120/208v 3 phase power to feed panels) but anyway they wouldnt let me fix the problem for some reason, but anyway was i correct with the term floating neutral? heres my guess on whats causing that (i didnt get to troubleshoot so its just a guess) XO on the transformer feeding the panel might not be grounded. anything wrong with that guess?

also the engineering department are not really engineers i think. they just fix stuff thats broken
 

iwire

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Staff member
electricalperson said:
heres my guess on whats causing that (i didnt get to troubleshoot so its just a guess) XO on the transformer feeding the panel might not be grounded.
IMO you are right, XO would be my first stop.
 

e57

Senior Member
I usually make a pit stop on the way to the XO - at the panel feeding them. Usually easier to find, and saves you a lot of effort if it is only in a J-box right next to the outlet(s) in question. One of my rules of troubleshooting is to split the circuit in half - follow the bad half, and split it, etc - so on.....

Two things:

BTW it's not a situation to take lightly - Floating/lost neutrals (AKA 'High/low voltage event') can be very serious to the point where equipment or appliances are damaged and causes a fire. I'm sure there are many who have let the smoke out of things in this way.

And since your neutral and ground differ quite a bit - this may be a difficult find. As the ground may only be an ungrounded or partially hot from a boot-leg neutral someplace - either way a shock hazard at the bar. Did you check voltage from the ground of the outlet to say a sink plumbing fixture - or nearby appliances and such? I have seen a few situations where a neutral or even a hot can energize say a stainless counter top and act as a load - and in your situation from another phase... (As only the ground and not the neutral is showing a higher than nominal voltage.)

Both ways can be a fire or shock hazard.
 

iwire

Moderator
Staff member
e57 said:
I usually make a pit stop on the way to the XO - at the panel feeding them.
Why would you go to the panel first?


Usually easier to find, and saves you a lot of effort if it is only in a J-box right next to the outlet(s) in question.
How could this problem be in a j-box next to the outlets?

One of my rules of troubleshooting is to split the circuit in half - follow the bad half, and split it, etc - so on.....
That is not exactly your rule, that is basic common sense. :D

But the NEC requires the bonding jumper to be in either, or both, of two places. The transformer or the first disconnecting means. Because of the limited distances allowed for transformer secondaries if your at the first disconnecting means you should also be at the transformer.

BTW it's not a situation to take lightly - Floating/lost neutrals (AKA 'High/low voltage event')
Given the voltage readings this is without a doubt a bonding jumper issue.

electricalperson said:
L to N 119 volts

L to G 136 volts

N to G 45 volts
The L to N is 119 which pretty much rules out a lost neutral.
 
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e57

Senior Member
iwire said:
Why would you go to the panel first?

Why would you assume that there only be an open between ground and grounded only at the transformer? Was everything in the whole area the transformer is serving affected?


How could this problem be in a j-box next to the outlets?

And open or resistive ground could be anywhere along the circuit.

That is not exactly your rule, that is basic common sense. :D

True - which is why I split things in half. :D While a bonding jumper could well be from what little either you or I see from this side of the screen as the issue - the possibility remains that it might not be.... So why start at the begining if there is the slightst possibility of ending up somewhere in the middle?

But the NEC requires the bonding jumper to be in either, or both, of two places. The transformer or the first disconnecting means. Because of the limited distances allowed for transformer secondaries if your at the first disconnecting means you should also be at the transformer.

And the panel right next to that, and this outlet right on the other side of the wall they are all on. ;)

Given the voltage readings this is without a doubt a bonding jumper issue.

It could be an intentional or un-intentional boot-leg neutral from another ciircuit IMO? It could be an open ground and the infamous 'ghost voltage' - as mentioned many times I do not beleive in ghosts... But since it is higher than nominal hot to ground and the math adds up for neutral to ground - I would think energized from another phase. It could be a lot of things IMO. :-? It could be you're right?

The L to N is 119 which pretty much rules out a lost neutral.

One would tend to think so - but since I'm on this side of my monitor, and and only know about readings taken at a single outlet near a bar - why rule anything out. :rolleyes:
Anyway, I think half both the discovery phase of troubleshooting, and learning begins with following a logical process. I think you get what I mean right?:rolleyes:
 

e57

Senior Member
electricalperson said:
the lady at the bar area called me over and asked me to look at her lights and plugs that didnt work.
So what was wrong with them? Sounds like the oulet in question would have worked fine - outside of being a potential hazard.
 

iwire

Moderator
Staff member
e57 said:
Anyway, I think half both the discovery phase of troubleshooting, and learning begins with following a logical process. I think you get what I mean right?:rolleyes:
Yes, and IMO given the conditions I would go to XO / first disconnect first.
I would not try to figure out where half way was until I determined each end.

To each their own.
 

electricalperson

Senior Member
Lxnxjxhx said:
Dear E. Person:

So that I can follow along, can you tell me which of the configurations in the site below you are using? I'd like to do the whole analysis, etc., with unbalanced loads and so on, to see if I can get your voltages.
Thanks.

http://insayne_kokane.tripod.com/transformers.shtml

Regards,

H. Person
im pretty sure the transformer was a 480/277 delta primary to a 120/208 volt wye secondary. like i said i didnt troubleshoot anything since they wouldnt let me for some reason. i think the maintanence department likes to play electrician
 

electricalperson

Senior Member
e57 said:
So what was wrong with them? Sounds like the oulet in question would have worked fine - outside of being a potential hazard.
if theres a floating neutral it wouldnt work. her appliances didnt work in any of the outlets she told me and none of the lights didnt work. like i said all i did was do a quick test on a receptacle that she was using and noticed the weird voltages. im assuming its a floating neutral because of what the meter said. she had a power strip that had a light on the button and the light was very faint when it was turned on
 

Buck Parrish

Senior Member
electricalperson said:
today i was doing a fire alarm system at a local hotel. the lady at the bar area called me over and asked me to look at her lights and plugs that didnt work. i took out my shiny new T+pro tester and stuck it in the receptacle and heres what i got.

L to N 119 volts

L to G 136 volts

N to G 45 volts

i called the "engineering" department and explained to them that they have a floating neutral and it should be fixed. (theres also receptacles in other parts of the buildings that dont work, not sure if its related or not and also a bunch of transformers for 120/208v 3 phase power to feed panels) but anyway they wouldnt let me fix the problem for some reason, but anyway was i correct with the term floating neutral? heres my guess on whats causing that (i didnt get to troubleshoot so its just a guess) XO on the transformer feeding the panel might not be grounded. anything wrong with that guess?

also the engineering department are not really engineers i think. they just fix stuff thats broken


I would have told her after that reading I got. I would need a drink in order to think about it.
 

crossman

Senior Member
The OP said the receptacles didn't work, but still measured 119v from L to N. This does not sound like a missing SBJ at the XO terminal. Sounds to me like a bad neutral connection somewhere between the xfmr and the receptacle. As someone mentioned, the 119v was an ohm's law reaction to a high impedance meter and a relatively lower impedance in series with the neutral.
 

electricalperson

Senior Member
if the neutral was grounded, the voltage would be stable. no ground on the neutral makes funny stuff happen sometimes. theres also a bunch of receptacles in the kitchen area that dont work either.
 

iwire

Moderator
Staff member
iwire said:
How could this problem be in a j-box next to the outlets?
e57 said:
And open or resistive ground could be anywhere along the circuit.
No, that condition alone can not result in these measurements.

L to N 119 volts

L to G 136 volts

N to G 45 volts
I don't care how resistive the EGC is, it will not result in a N to G voltage of 45 volts. (Not by itself, perhaps with a second fault as well)


Why would you assume that there only be an open between ground and grounded only at the transformer?
Because they should be open every but there, and if they where connected the potential between them would be much less then 45 volts.
 

electricalperson

Senior Member
crossman said:
The OP said the receptacles didn't work, but still measured 119v from L to N. This does not sound like a missing SBJ at the XO terminal. Sounds to me like a bad neutral connection somewhere between the xfmr and the receptacle. As someone mentioned, the 119v was an ohm's law reaction to a high impedance meter and a relatively lower impedance in series with the neutral.
thats also possible. nothing was taken apart and no troubleshooting done, just a quick test with the t+pro
 

crossman

Senior Member
If there was a poor neutral connection somewhere between X0 and the receptacle, the portion of the neutral connected to the receptacle would not be at ground potential.

Why would a missing system bonding jumper at X0 cause the receptacles not to work even though there was a measured 119v there?
 

iwire

Moderator
Staff member
crossman said:
Why would a missing system bonding jumper at X0 cause the receptacles not to work even though there was a measured 119v there?

(theres also receptacles in other parts of the buildings that dont work, not sure if its related or not
I am assuming that it is unrelated.
 

crossman

Senior Member
Hmmm.... I can see we could get the 119v LN and the 45v NG but to get the 135 LG then there does need to be another poor or missing connection somewhere I think.

 
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