124v Hot to Neutral

[Aegis]

First post

Another electrician hooked up some lights in a commercial building, 120v lights 3 phase system. When he turned the breaker on the lights didn't come on. He held up his pen tester to the light and it lit up while standing a foot away from the light. So he calls me and explains. I said the neutral isn't tied in the panel, that's why his pen tester is lighting up from a foot away from the BX feeding the first light. He pulled out his meter and opened the light. He got 118v from hot to ground, then he checked between hot to neutral and got 124v. That is the part I don't understand, if he's getting voltage between hot and neutral, the circuit has a path back to it's source and the lights should be on. Everything led me to believe it's an open neutral at he panel. Is there any other way to get 124v between hot and neutral? I'm stumped lol

 

[iwire]

First post

Another electrician hooked up some lights in a commercial building, 120v lights 3 phase system. When he turned the breaker on the lights didn't come on. He held up his pen tester to the light and it lit up while standing a foot away from the light. So he calls me and explains. I said the neutral isn't tied in the panel, that's why his pen tester is lighting up from a foot away from the BX feeding the first light. He pulled out his meter and opened the light. He got 118v from hot to ground, then he checked between hot to neutral and got 124v. That is the part I don't understand, if he's getting voltage between hot and neutral, the circuit has a path back to it's source and the lights should be on. Everything led me to believe it's an open neutral at he panel. Is there any other way to get 124v between hot and neutral? I'm stumped lol

My guess.

The neutral has a bad connection or is open and reading through another load that is why it is 118 and not making the light come on.

The 124 volt reading to ground is good and I bet you have 124 at the panel.

 

[Sierrasparky]

First post

Another electrician hooked up some lights in a commercial building, 120v lights 3 phase system. When he turned the breaker on the lights didn't come on. He held up his pen tester to the light and it lit up while standing a foot away from the light. So he calls me and explains. I said the neutral isn't tied in the panel, that's why his pen tester is lighting up from a foot away from the BX feeding the first light. He pulled out his meter and opened the light. He got 118v from hot to ground, then he checked between hot to neutral and got 124v. That is the part I don't understand, if he's getting voltage between hot and neutral, the circuit has a path back to it's source and the lights should be on. Everything led me to believe it's an open neutral at he panel. Is there any other way to get 124v between hot and neutral? I'm stumped lol

did you use a solenoid type testor?

 

[Smart $]

Welcome. :thumbsup:

Any chance of an open neutral on the load side of where he is measuring 124V to neutral?

Basically asking where did he measure this 124V from hot to neutral? Was he using a high- or low-impedance voltmeter?

 

[Jraef]

did you use a solenoid type testor?

And now launch the debate as to the value of a "Wiggy"...

Aegis,
First off, welcome to the forum!

In case you are not familiar with them, as many younger electricians apparently are not, a "Solenoid tester" is an old fashioned hand held AC voltage tester that gives you a voltage readout on an analog scale based on the voltage causing an actual solenoid to pull in. The higher the voltage, the stronger it pulls the indicator along the scale. The original was named a "Wiggy" after the inventor, then the company was bought by Square D. Years later when the patent ran out, another company called Knopp made one, so a lot of electricians also call them "Knopp testers" or just "Knopps".

The value of this over a Digital Multi Meter (DMM) is that the DMM is measuring and displaying the voltage it reads, but puts almost no "burden" or load on the circuit itself. This is important when reading some electronic circuits, but presents a problem in AC situations like this for precisely the reason Iwire brought up; the DMM is reading THROUGH (in series with) another load on the same circuit. If the tester was a Wiggy, the load of its solenoid would cause a voltage drop on that series circuit and read close to nothing. In other words you are reading something that is technically a complete circuit, but only because of the extreme sensitivity of that type of meter. In a practical sense, you likely have, as you suspected, an open neutral somewhere. But one thing you do know from this; the open neutral is probably NOT at the panel connection, otherwise the DMM reading through the other liad would not be there either.

 

[K8MHZ]

First post

Another electrician hooked up some lights in a commercial building, 120v lights 3 phase system. When he turned the breaker on the lights didn't come on. He held up his pen tester to the light and it lit up while standing a foot away from the light. So he calls me and explains. I said the neutral isn't tied in the panel, that's why his pen tester is lighting up from a foot away from the BX feeding the first light. He pulled out his meter and opened the light. He got 118v from hot to ground, then he checked between hot to neutral and got 124v. That is the part I don't understand, if he's getting voltage between hot and neutral, the circuit has a path back to it's source and the lights should be on. Everything led me to believe it's an open neutral at he panel. Is there any other way to get 124v between hot and neutral? I'm stumped lol

I have seen this with the hot and neutral reversed at the light, and also when neutrals are switched.

Check for voltage from the lamp socket shell to ground and see what you get.

 

[dmxtothemax]

First post

if he's getting voltage between hot and neutral, the circuit has a path back to it's source and the lights should be on. l

WRONG !

he may be getting 120v ? but at what current level ?
Enough current to trick a non contact tester or digital volt meter
But not enough to do anything else.
This is known as a current limit, or high resistance joint.
Put a real load on it like a 100w lamp
and watch that 120v diss-appear real quick !

 

[JFletcher]

Welcome

First post

Another electrician hooked up some lights in a commercial building, 120v lights 3 phase system. When he turned the breaker on the lights didn't come on. He held up his pen tester to the light and it lit up while standing a foot away from the light. So he calls me and explains. I said the neutral isn't tied in the panel, that's why his pen tester is lighting up from a foot away from the BX feeding the first light. He pulled out his meter and opened the light. He got 118v from hot to ground, then he checked between hot to neutral and got 124v. That is the part I don't understand, if he's getting voltage between hot and neutral, the circuit has a path back to it's source and the lights should be on. Everything led me to believe it's an open neutral at he panel. Is there any other way to get 124v between hot and neutral? I'm stumped lol

Is there a photocell or occupancy switch in the loop? It shouldnt break the neutral but that could be it. Have the correct bulbs in there? Ballasts wired from 120V tap, not 277V?

If the neutral is good back to the panel (and not switched), you will have continuity between neutral and ground.

and yes, there is a way to get 124V between hot and neutral: what do you think a DMM will read when you check a receptacle that's wired properly?

Non contact tester test doesnt tell you much. I can hold mine 5" from an incandescent light (or 1" from the socket/wire) before it alarms, yet the LED screen on this laptop will trigger it at almost 2' away. I'm not being shocked or electrocuted while I type this reply.