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Unread 06-20-2019, 09:48 PM   #1
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Default How to test if shared neutral is live?

Hello,

I'm working in a building where there are some circuits (3 phase 347/600v circuits) that share a neutral. The junction box I'm working on has one live circuit with neutrals spliced, I already shut the live wire off, but unsure if the neutral is shared or not, and want to test it. The non contact voltage tester doesn't work on live shared neutrals of course, but using a multimeter will only show little to no voltage on a neutral. So what's the best way to determine if a neutral is completely dead?
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Unread 06-20-2019, 09:59 PM   #2
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Quote:
Originally Posted by vhk View Post
Hello,

I'm working in a building where there are some circuits (3 phase 347/600v circuits) that share a neutral. The junction box I'm working on has one live circuit with neutrals spliced, I already shut the live wire off, but unsure if the neutral is shared or not, and want to test it. The non contact voltage tester doesn't work on live shared neutrals of course, but using a multimeter will only show little to no voltage on a neutral. So what's the best way to determine if a neutral is completely dead?
Hang a clamp on meter and see if there is current flowing.
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Unread 06-20-2019, 10:06 PM   #3
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Are you an electrician, an apprentice, a maintenance person or something else???
Please fill out your profile.
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Unread 06-20-2019, 10:14 PM   #4
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even a zero amp unless you can prove the neutral is dead then you treat it as a live wire and use PPE.
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Unread 06-21-2019, 01:07 AM   #5
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Unread 06-21-2019, 01:09 AM   #6
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Unread 06-21-2019, 08:22 PM   #7
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Easy.....cut it and if something burns up, it was live.......

Seriously, I don't know of any way to know if it's carrying current or not. If the current is very low, a clamp-on won't read it.
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Unread 07-07-2019, 02:26 AM   #8
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You start by tracing out the wires for A, B, C phase to a point of disconnect and shut off all three phases. They should be on either a 3-pole breaker or 3 single-pole breakers with approved handle-ties, but being realistic here, they probably aren't.


Then you still cap it and treat it as if it is live. You can verify dead following proper procedures.


More importantly, is no one around to teach you this?


Also, you shouldn't be working with a circuit at those voltages, and likely ampacities...


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Unread 07-07-2019, 07:47 AM   #9
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Welcome aboard @vhk!

Thanks for filing out your profile.

I'm of the camp that this should have been explained by your journeyman, if you came here I figure you aren't comfortable asking or he's not easy to ask questions.

Always ask questions, it's a part of learning.
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Unread 07-07-2019, 11:05 AM   #10
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Quote:
Originally Posted by sparkiez View Post
You start by tracing out the wires for A, B, C phase to a point of disconnect and shut off all three phases. They should be on either a 3-pole breaker or 3 single-pole breakers with approved handle-ties, but being realistic here, they probably aren't.


Then you still cap it and treat it as if it is live. You can verify dead following proper procedures.


More importantly, is no one around to teach you this?


Also, you shouldn't be working with a circuit at those voltages, and likely ampacities...


IT


WILL


KILL


YOU
Not required in Canuckistan.. But very important to determine which hots they are, because as you mentioned it will kill you. 347 is nothing to mess around with.. Is the wiring labelled? The neutrals may be labelled to help determine which hots are included. Is it ran in a conduit that can be traced, so that you narrow down your search?
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Unread 07-07-2019, 05:17 PM   #11
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Thanks for the responses everyone. First of all, I'm posting here not because I'm unsure or afraid of asking my Jman, I'm posting here because it appears a lot of people at my work, as well as other electricians I ask, don't seem to know how to test for a live neutral right on site without having to go through the trouble of identifying if a neutral has all the phases shut off.

First of all, I'm mostly working commercial service. A lot of places I go to involve large downtown buildings where 347v lighting is prevalent. The buildings are quite old, so the neutrals are not labelled as to what hots are sharing them, both at the JBs and panelboard. There are hundreds to thousands of people working in these buildings., so a lot of times we are expected to service live circuits without inconveniencing the people working inside. Current job I have to do is removing old 347v lighting and their corresponding BX whips from the JBs.

The JBs contain a bunch of neutrals spliced together. I already shut off the hot for the light themselves, but wanted to see if the neutral is completely dead before I break apart the neutrals. My Jman mentioned to me I just put a clamp meter on the neutral, but I know it doesn't work if the current is low enough. The circuit is #2 on the panelboard, and I know typically shared neutrals go sequentially like 2,4,6 - N, or 2,4-N, etc. But shutting off the other breakers would either shut off lighting to most of the building with people inside, and it may not guarantee the neutral is dead, as #2 can be shared with #10,#12, for example. Panelboard and JBs have no labeling. Conduit and wires cannot be traced due to the layout of the building. That's why I want to know what's the best way to ensure a neutral is dead, right on site.
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Unread 07-07-2019, 05:19 PM   #12
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Just to add, I was able to shut off the breaker for those lights, just because that entire floor of the building happened to be vacant, so nobody was inconvenienced, but the rest of the floors are occupied.
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Unread 07-07-2019, 10:39 PM   #13
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If you're just demoing lights, cut the neuch for the whip your working on at the connection leaving yourself enough sticking out of the wirenut to cap with a yellow, or tape it. No need to open the splice. Just don't ground yourself while cutting.
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Unread 07-08-2019, 12:28 PM   #14
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Originally Posted by joebanana View Post
If you're just demoing lights, cut the neuch for the whip your working on at the connection leaving yourself enough sticking out of the wirenut to cap with a yellow, or tape it. No need to open the splice. Just don't ground yourself while cutting.

This isn't wrong, but it makes me damn uncomfortable sending someone who hasn't been trained to deal with this high-energy of a circuit...
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Unread 07-08-2019, 12:45 PM   #15
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F those bunch of desk riding sissies. "Inconvienced". I'm the last guy to preach about working live, especially on 20 amp lighting circuits. I do it all the time depending on the situation. None of those situations are ever because it inconviences someone in front of a computer. Turn it off.
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Unread 07-08-2019, 01:03 PM   #16
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F those bunch of desk riding sissies. "Inconvienced". I'm the last guy to preach about working live, especially on 20 amp lighting circuits. I do it all the time depending on the situation. None of those situations are ever because it inconviences someone in front of a computer. Turn it off.
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Unread 07-08-2019, 01:10 PM   #17
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Unread 07-08-2019, 01:34 PM   #18
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Just don't open the circuit. Do as Joebanana says just cut the whip wires and nut it. Opening the circuit can send mixed voltages to the load.
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Unread 07-08-2019, 06:24 PM   #19
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I've been at this a while, and you won't catch me working a 600V phase to phase circuit hot. Either people are working in the dark or I'm getting double time to do it during the off-hours. Not long ago a kid died hanging exit lighting. He graduated from a trade school, the company lied to him about being a registered apprentice. He was listed as a laborer. They ****ed him over, he wasn't being supervised, and now he is dead.


Hearing something like this makes me want blood.
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Unread 07-08-2019, 06:34 PM   #20
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Originally Posted by sparkiez View Post
I've been at this a while, and you won't catch me working a 600V phase to phase circuit hot. Either people are working in the dark or I'm getting double time to do it during the off-hours. Not long ago a kid died hanging exit lighting. He graduated from a trade school, the company lied to him about being a registered apprentice. He was listed as a laborer. They ****ed him over, he wasn't being supervised, and now he is dead.


Hearing something like this makes me want blood.
Me too. No one should be working on live circuits unless your licensed and only troubleshooting. Definitely should not have a brand new worker doing it.


Just to clarify, he did not graduate from a trade school. He paid for a money grab, pre apprentice scam of a school where everyone graduates as long as you pay. They charge $9000 for 3 month program that gets you nothing. No hours toward a real apprenticeship, no real trade school exemptions.

Sorry, these pre apprentice money grab scams are a bit of a trigger for me.
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