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.
Re: 120v and 277v in the same box?#49486 03/07/0509:15 PM03/07/0509:15 PM
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.
Re: 120v and 277v in the same box?#49487 03/07/0509:18 PM03/07/0509:18 PM
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).]
Re: 120v and 277v in the same box?#49489 03/09/0506:10 PM03/09/0506:10 PM
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.