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#49483 - 03/07/05 08:20 PM 120v and 277v in the same box?  
GA76JW  Offline
Joined: Mar 2004
Posts: 193
Suwanee, GA USA
We have a formean at work who is bent on feeding a 1900 box (4x4) for a neon light(apparently 120V) thru the same pipe run that is feeding the outside lighting (277V).

Now my question stems from this. Everyone I have talked to says it is not a good thing to do, but no one can tell me where it is in the code book or why it is not correct.

Magnetic lines of flux was brought up, but no one could give a definate answer.

Anyone know?

"If common sense was common, everyone would have it"-not sure, someone here

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#49484 - 03/07/05 08:32 PM Re: 120v and 277v in the same box?  
Roger  Offline
Joined: May 2002
Posts: 1,716
GA76Apprentice, although it may seem a little odd, it is allowed, see 300.3(C). Take note that the insulation in your question would only have to be 300 volts on any conductor if the question arose.


[This message has been edited by Roger (edited 03-07-2005).]

#49485 - 03/07/05 08:56 PM Re: 120v and 277v in the same box?  
Gregtaylor  Offline
Joined: Mar 2005
Posts: 212
Boise, Idaho, USA
While it may not be a great idea, as it tends to confuse the next guy, there is nothing in the code that prohibits this, in general. Following the high voltage/low voltage color code is helpful and so is careful labeling, but as long as the insulation of all wires is at least 300 volts,(THHN is 600 volt) its OK.

#49486 - 03/07/05 09:15 PM Re: 120v and 277v in the same box?  
CRM  Offline
Joined: Feb 2004
Posts: 74
Alberta Canada
I also don't like it, different voltages in the same conduit can induce voltages into the other conductors. Safety is also a factor with different voltages all in the same junction box. I have to agree with the Canadian Electrical Code, its not allowed except for the supply and control of remote devices, like a motor starter, if all conductors are insulated for the highest voltage.

#49487 - 03/07/05 09:18 PM Re: 120v and 277v in the same box?  
Celtic  Offline
Joined: Feb 2005
Posts: 361
try 200.6(d)...and watch grounded/grounding color markings.

I am NOT in favor of mixing voltages, the code has a provision for it.

[This message has been edited by Celtic (edited 03-07-2005).]

~~ CELTIC ~~
...-= NJ =-...

#49488 - 03/08/05 09:06 AM Re: 120v and 277v in the same box?  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Someone correct me if I'm wrong, but the magnetic lines of flux issue only exists when current is flowing and it is not related to mixed voltages (at least at that level).
For example, even if the voltage level is the same, if one circuit is loaded, and the other is shut off at the supply, it is possible that the loaded circuit will induce a voltage in the wires in the other circuit.
As was stated, maybe not a good idea, but if the prospect of running a new conduit versus using an existing one is economically questionable, there is no NEC article to prohibit it.
I agree with Celtic. Not color coding the Neutrals is a good way to possibly hurt someone in the future.

[This message has been edited by Redsy (edited 03-08-2005).]

#49489 - 03/09/05 06:10 PM Re: 120v and 277v in the same box?  
GA76JW  Offline
Joined: Mar 2004
Posts: 193
Suwanee, GA USA
Well for starters. We labeled the box as best we could and numbered the wires. The 277V were a brown and yellow circuit with a grey neutral and the 120V was a black with a white neutral.

Everyone I have talked to about this thinks it is not a good idea for the alot of the reasons listed above.

I appreciate all the replies so far.

"If common sense was common, everyone would have it"-not sure, someone here

#49490 - 03/09/05 06:20 PM Re: 120v and 277v in the same box?  
Celtic  Offline
Joined: Feb 2005
Posts: 361
How were the grounds addressed?

~~ CELTIC ~~
...-= NJ =-...

#49491 - 03/09/05 06:32 PM Re: 120v and 277v in the same box?  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I do not see any reason not to mix the two voltages in the same box, as long as the requirements of 200.6(D) are met.

Having one circuit of 277 and another circuit of 120 in the same box is no more dangerous than having two 120 or two 277 volt circuits in the same box.

120 can kill you as quick as 277, you should not work on either live.

When you open a box with multiple conductors you should never assume there is only one circuit contained in that box regardless of the number of supply voltages.

If you can not mix voltages you might as well say you may only have one circuit of any type in a box.

We are 'qualified' personal aren't we? [Linked Image]


Bob Badger
Construction & Maintenance Electrician

#49492 - 03/09/05 09:39 PM Re: 120v and 277v in the same box?  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,099
The guys I have watched use some strict color coding to indicate what is going on in a box. Red, black and blue is 3p wye, 120v to ground with a white neutral. BOY is 480 L/L loads and 277 L/N loads are violet with a grey neutral. They used BOY tape to further identify violet conductors.
That may have just been a local convention but a quick peek in a box and you knew what you had going on. They also wrote the panel and breaker number on each box when they built the system.
These were state projects where the guy building it was also going to have to live with it so they spent the extra time on the front end to make life easier down the road.

Greg Fretwell

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dallas, texas, USA
Posts: 67
Joined: January 2002
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