277v lighting, hot neutral

[rrosario]

I've been an electrician for a few years, and have recently been entrusted with training an apprentice. I was trained to believe that you can't always read voltage on a 277v neutral wire when it's hot. This made sense to me in a 4 wire wye configuration, which is our primary lighting. Recently, I overheard one of our fourty year electricians telling this kid that I didn't know what I was talking about, that if the voltage is there, he can read it to ground. I only know what I was taught, and I could very easily be wrong, but if I am right, I want to be able to prove this to this young man before he gets hurt or worse.
unfortunately, we apparently used to parallel alot of our lighting, which just increases the likelyhood of hot neutrals, and also makes it very difficult to deenergize the fixture we may be working on, because you are then in total darkness. Any input would be appreciated. Thanks.

 

[Smart $]

I've been an electrician for a few years, and have recently been entrusted with training an apprentice. I was trained to believe that you can't always read voltage on a 277v neutral wire when it's hot. This made sense to me in a 4 wire wye configuration, which is our primary lighting. Recently, I overheard one of our fourty year electricians telling this kid that I didn't know what I was talking about, that if the voltage is there, he can read it to ground. I only know what I was taught, and I could very easily be wrong, but if I am right, I want to be able to prove this to this young man before he gets hurt or worse.
unfortunately, we apparently used to parallel alot of our lighting, which just increases the likelyhood of hot neutrals, and also makes it very difficult to deenergize the fixture we may be working on, because you are then in total darkness. Any input would be appreciated. Thanks.

If you attempt to read voltage to ground on a neutral wire in a properly connected and conducting multiwire branch circuit (i.e. at least one circuit conducting), the measurement will only indicate that of voltage drop of the current imbalance at that point in the circuit. Break the circuit at that point and both sides of the break could potentially be 277V to ground.

 

[iwire]

To add to what the post above pointed out. A voltage reading between the neutral of a multi wire branch circuit and the grounding conductor of more than 4 or 5 volts indicates a problem with the circuit.

Up to about 5 volts can be explained by voltage drop. If you see a reading greater than that a open or poorly connected neutral back to the panel should be suspected.

 

[brian john]

Break the circuit at that point and both sides of the break could potentially be 277V to ground.

Break the circuit and at the point of the open you should have 0-5 VAC on the end coming from the distribution panel (if there is any load still on this circuit). The other side of the circuit (towards the load) should read 277 VAC, if there is still load connected. If this is lighting and the light switches are off the reading should be 0 (zero).

 

[tomP]

Break the circuit at that point and both sides of the break could potentially be 277V to ground.

Break the circuit and at the point of the open you should have 0-5 VAC on the end coming from the distribution panel (if there is any load still on this circuit). The other side of the circuit (towards the load) should read 277 VAC, if there is still load connected. If this is lighting and the light switches are off the reading should be 0 (zero).

Wouldn't the voltgage reading depend on WHERE this this point of open is in the circuit?
At the panel "0" and 277V
In the middle of the circuit 277V both ends?
Considering the switch is on.

 

[winnie]

If you break the neutral on a circuit, the side of the break that is still electrically connected to the neutral bar in the panel will be near 0V, as determined by any voltage drop and current in the remaining portion of the circuit. The side connected to ungrounded conductors via any loads will be anywhere up to the full system voltage, depending upon the combination of loads on that side of the break.

-Jon

 

[tomP]

If you break the neutral on a circuit, the side of the break that is still electrically connected to the neutral bar in the panel will be near 0V, as determined by any voltage drop and current in the remaining portion of the circuit. The side connected to ungrounded conductors via any loads will be anywhere up to the full system voltage, depending upon the combination of loads on that side of the break.

-Jon

Boy, I must have gotten up too early today!
Neutral = 0 or near zero neutral bar side.
DUH!! Got it now.
Thanks

 

[rrosario]

Maybe I missed the point I was trying to make. If the hot lead to the 277v ballast is disconnected in the fixture, and I take a multimeter across the neutral to ground, should I be able to see the 277v that my neutral is still carrying from my parallel sources?

 

[realolman]

I've been an electrician for a few years, and have recently been entrusted with training an apprentice. I was trained to believe that you can't always read voltage on a 277v neutral wire when it's hot. This made sense to me in a 4 wire wye configuration, which is our primary lighting. Recently, I overheard one of our fourty year electricians telling this kid that I didn't know what I was talking about, that if the voltage is there, he can read it to ground. I only know what I was taught, and I could very easily be wrong, but if I am right, I want to be able to prove this to this young man before he gets hurt or worse.
unfortunately, we apparently used to parallel alot of our lighting, which just increases the likelyhood of hot neutrals, and also makes it very difficult to deenergize the fixture we may be working on, because you are then in total darkness. Any input would be appreciated. Thanks.

rrosario,
I wonder if you would mind explaining this post a little more... there are a few phrases like "can't always read voltage on a 277v neutral when it's hot" that I don't understand."

 

[winnie]

Maybe I missed the point I was trying to make. If the hot lead to the 277v ballast is disconnected in the fixture, and I take a multimeter across the neutral to ground, should I be able to see the 277v that my neutral is still carrying from my parallel sources?

No, you will not. You will see any 'voltage drop' in the neutral conductor caused by the current flowing through it, but this should be no more than a couple of volts. You could probably touch this conductor with no more than a slight tingle (but you shouldn't try this!).

The _danger_ of this conductor is when you _break_ it. As long as it remains connected back to the panel, the metallic connection holds the voltage low. But as soon as you break the connection, the voltage can rise up to the dangerous 277V level.

The danger is that you have a conductor which meters at low voltage. You disconnect this conductor, and suddenly it is at a shocking voltage.

-Jon

 

[Smart $]

To clarify to all in this branch of the thread, my statement...

Break the circuit at that point and both sides of the break could potentially be 277V to ground.

...was made from a safety standpoint. Yes, the voltage potential of the line side of the break should be at or near zero... but I said "could potentially be 277V" and it very well could be if there is a continuity problem on the line side of the break. When one breaks a circuit neutral, it should neither be assumed which side is the line side nor that the voltage potential is at or near zero. Verify by means other than one's own body before proceeding is all that was meant by my statement.

 

[mdj1320]

they say the neutral hits you harder than the hot

 

[brian john]

they say the neutral hits you harder than the hot

Only because you weren't expecting it.

 

[pfalcon]

To the OP

In a perfect world
Neutral V = Ground V

In a correctly wired world

Yes, the voltage potential ...(edit) should be at or near zero...

In a world where shorts and breaks occur

"could potentially be 277V"

 

[plugster]

My lesson

My lesson

When I was green and just carried the ladder, I saw a co worker fall off a 12 foot ladder because of a "hot" neutral. Taught me a huge lesson. Cap hot and grounded when changing ballast, and not to touch anything until....

 

[LarryFine]

If the hot lead to the 277v ballast is disconnected in the fixture, and I take a multimeter across the neutral to ground, should I be able to see the 277v that my neutral is still carrying from my parallel sources?

No, but if you open a neutral junction that still has hot ballasts connected downstream, you will read voltage between that side of the break and ground.

This is why so many people disdain multi-wire branch circuits. However, if properly wired and protected, and properly de-energized, there is little danger.

 

[mattsilkwood]

Only because you weren't expecting it.

but if you get between a 277 nuetral youve got big problems. it will use you to make the circuit. i seen a guy do this ,it hit him so hard it blew out his csrpal tunnel in his wrist and elbow. but if there is a load on it an amp meter will tell you.

 

[LarryFine]

. . . if there is a load on it an amp meter will tell you.

And if it's not at (or near) zero to ground, a non-contact tester will tell you.

 

[mattsilkwood]

And if it's not at (or near) zero to ground, a non-contact tester will tell you.

very true but the thing i dont like about a hot stick is there not 100% right 100% of the time.

 

[Smart $]

very true but the thing i dont like about a hot stick is there not 100% right 100% of the time.

A clamp-around ammeter (aka amp meter) will only tell you if a wire is conducting... it will not tell you 100% of the time if a wire is energized, nor will it tell you the future, as in when a switch will be flipped.

With proper usage methods and knowing when it gives accurate indications, I find my NCVS quite reliable... but that 0.0001% is enough for me to take other precautionary measures. It is 100% reliable if indication changes coincidentally to flipping the right switch a couple, few times :grin: