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[Jeff Bankston]

The problem with using white for all neutrals is that the neutral for a 277 system is not he same as a neutral for a separately derived (transformer) 208 system.  I am dealing with a building now where a previous contractor ran both 277 V and 120 V lighting circuits in the same conduit.   If I cross a neutral in a box, I wind up with the current from the 120 V system getting back to the 277 V neutral via the associated bonding-not a good situation.  Code does require identifying  neutrals from different systems by using a white wire with a stripe-they can be pretty hard to find.

It seems like using gray has been a common industry practice, even though Jeff is right.  Interestingly, a code panel rejected allowing gray to be used because it felt that white and gray would not always be distinguishable in the same box.  That reasoning would seem to preclude using gray as a hot conductor as well, but what do I know?

Update:

Actually just looked at the 2011 NEC. The term "natural gray" is no longer used.  The 2011 NEC specifically allows Conductors with    200.6 (A) (1)"A continuous white outer finish"  and 200.6 (A)(1) "A continuous gray outer finish" to identify a neutral.

NEC 200.7 specifically prohibits using a conductor with a "gray covering" from being used as a hot.

The other discussions regarding a read about took place at least 4 code cycles ago.  I am still using the 2011.  2014 is "out" but not being used yet where I am.

its illegal to run 2 different power voltages in the same condiut. i have never seen or heard of it done. you would need to come out of the 480/277 panel into a gutter or pull can and also come out of the 120/208(240) panel into the same gutter. now your mixing voltages which is illegal. 2 phases of 277 in the same can and condiut is 480v. brown,orange,yellow wire is use for 277/480 with black,red,blue,purple,pink used for switch legs. someone doing service/add-on work could tie a 120v recptical into a 277 leg. i'v seen a lot of illegal stuff done but never mixed voltages. many many years ago in downtown los angeles GREEN was use as a hot leg in some buildings. i found out the hard way. also i was talking to an electrician friend earlier today and he did some work on an old house with black pipe that had gray for the hot and white for the neutral, no ground wire. old plugs with no ground hole.

[Stephen Swaffer]

I would agree that mixing different voltage systems is poor practice-and I wish it would not have been done this way.  However code specifically states that neutrals from different systems in the same raceway or box must be identified.  In most cases different systems would mean different voltages-this would seem to indicate that it is allowable-I am not trying to argue, I would like to know the code reference, I just haven't found it yet.

If someone is tying in a receptacle, I would hope they shut off the breaker-and if working in a facility with 480/277 I would hope they would recognize the difference between a 120/208 breaker and a 480/277 breaker and hopefully the panels are marked, too.  Good workmanship also says to test that receptacle when done and verify that it is right-that should prevent a problem.

[Mike Sokol]

I would agree that mixing different voltage systems is poor practice-and I wish it would not have been done this way.  However code specifically states that neutrals from different systems in the same raceway or box must be identified.  In most cases different systems would mean different voltages-this would seem to indicate that it is allowable-I am not trying to argue, I would like to know the code reference, I just haven't found it yet.

Another weird one to consider is 4-wire/3-phase wild/high/red/bitch-leg Delta, typically with 120, 240 and 208 volts available on the same wires in the same panel, just depends on how you hook up which phase(s). Of course the "high" leg is supposed to be marked with "orange" tape in the panel, but I don't know if that translates to a different wire color downstream. This was common in older 3-phase factory power from the 50's and 60's IIRC, but I've found it a few times in repurposed industrial buildings that have been turned into concert venues, clubs, and churches. Measure twice / connect once.   See http://en.wikipedia.org/wiki/High-leg_delta for a primer.

[Jeff Bankston]

I would agree that mixing different voltage systems is poor practice-and I wish it would not have been done this way.  However code specifically states that neutrals from different systems in the same raceway or box must be identified.  In most cases different systems would mean different voltages-this would seem to indicate that it is allowable-I am not trying to argue, I would like to know the code reference, I just haven't found it yet.

If someone is tying in a receptacle, I would hope they shut off the breaker-and if working in a facility with 480/277 I would hope they would recognize the difference between a 120/208 breaker and a 480/277 breaker and hopefully the panels are marked, too.  Good workmanship also says to test that receptacle when done and verify that it is right-that should prevent a problem.

nope , cannot mix voltages. if your called to install a receptical on a wall with a tigerbox and you have a j-box with 277v lighting and 120v recepticals you cannot shut off those lightining circuts and leave people in the dark. i have come across many j-boxes that were not labeled and with wires that were not numbered and with 2 or 3 different neutrals. the business didnt have a set of as-builts or prints. i have also seen black red blue wire used in 277 systems in coundiut. i have done quite a few of these recepticals and was only allowed in the business/office building during work hours. i have move desk and removed t-bar tile with the employee(s) going about their work with me in there. i left a message with the local senior inspector to call me about this one. but everything i'v ever learned is you cannot mix 120 and 277 in the same condiut. 

p.s. about 20 years ago i came across an unlabeled j-box with a blue/white on one side connected to a yelow/white on the other side. i never did find where it went. it was a large 4 story building.

[Jeff Bankston]

Another weird one to consider is 4-wire/3-phase wild/high/red/bitch-leg Delta, typically with 120, 240 and 208 volts available on the same wires in the same panel, just depends on how you hook up which phase(s). Of course the "high" leg is supposed to be marked with "orange" tape in the panel, but I don't know if that translates to a different wire color downstream. This was common in older 3-phase factory power from the 50's and 60's IIRC, but I've found it a few times in repurposed industrial buildings that have been turned into concert venues, clubs, and churches. Measure twice / connect once.   See http://en.wikipedia.org/wiki/High-leg_delta for a primer.

the "kicker leg" as some of us call it must be an orange wire or marked with orange phase tape if its larger than #6. in california the kicker leg is C phase at the service and then goes to B phase at the breaker panel. i think thats stupid but its the way cali does it. theres lots and lots of 120/240 3 phase 4 wire systems here in los angeles. newer areas get 120/208 3 phase 4 wire sytems but it seems the 120/240 is the dominant one. a friend owned a building about 100 years old in Pomona. i rewired it for him. it had 2 seperate services. a 120/220 single phase 3 wire service and straight 240 3 phase 3 wire system for compressors, air cond , etc. no neutral for the 240 system. i was looking at the ;power pole and the 240 service ended at his building.

[Stephen Swaffer]

I rarely trace wires back to ID a breaker-most of the time j-boxes are unmarked.  Breaker panels should be marked with voltage and breakers should be marked, but over time the markings become less reliable as work is done and things are changed.  Mike gave a great idea for IDing a circuit without turning it off in another thread.

NFPA 70E  deals with arc flash and energized work-ie installed recepts on an energized circuit.  One tool it gives electricians is a requirement that before energized work is done, a "Hot" or "Energized" work is done a permit must be filled out.  There is something about requiring management to justify not turning off a circuit AND signing their name to a permit that spells out the potential dangers that often facilitates a change of heart about not shutting off that circuit for a few minutes so work can be done safely.  A company policy to that effect might come in handy on some jobs.

[Geri O'Neil]

Based on the title of this thread, I was thinking maybe a new and really twisted Rod Stewart song.

Geri O

[Steve M Smith]

It sounds like the whole of the power distribution system in the US needs to be scrapped and you should use a simple system like ours!


Steve.

[Mike Sokol]

It sounds like the whole of the power distribution system in the US needs to be scrapped and you should use a simple system like ours!


Steve.

As I've noted before, the US was the original test-bed for power distribution via inventions from Edison and Tesla, so a lot of early power was bleeding edge. There were numerous band-aids applied to early power systems to avoid the expense of starting over, which has created a plethora of wiring strategies in the US, many still in operation today. At least we've finalized on 60 Hz here and 50 Hz in much of Europe. But there were a bunch of different frequencies tried, starting with 25 Hz generators at Niagra Falls. See charts below. Talk about some strange sounding "hum".

[Steve M Smith]

At least we've finalized on 60 Hz here and 50 Hz in much of Europe. But there were a bunch of different frequencies tried, starting with 25 Hz generators at Niagra Falls.

I have seen old advertisements for Gibson amplifiers with a 25Hz (more likely 25c/s) option.


Steve.

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