ECN Forum Forums General Topics of the Trade General Discussion Area 208, 240, & 277 volt questions

"anyone ever seen an application where 277/480v was used, using NM? "

well i did see few place did use the NM on 277/480 circuit but tell ya the truth it was kinda spooky on me but if my memory serve me right in history way back in WW2 era they did use the NM alot on 480 volt circuit to save steel that time but currently it about nonexitsing now .

ps if this person ask about 277/480 volt system this is very common on large commercal/industrail area and quite few store did ran on 277/480 due large number of lighting system

Merci, Marc

[This message has been edited by frenchelectrican (edited 04-23-2006).]

norcal, Look in the NEC 2005, Art 334.10, 334.12.
Have you ever seen NM in a commercial building? I haven't,except for someones handymans work, rarely though.
--------------------------------------------Larry Fine, In many commercial/industrial panels there will be 3 phase, 2-120v to ground legs, and 1-208v to ground leg, but they will measure 208 volts between each hot leg. I know the transformers are set up that way, but when would you use the 208v to ground, leg. Most commercial motors are 3 phase 120/208/v or 277/480v, or sometimes 120/208v single phase.
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frenchelectrician, maybe in WW2, but I've never seen 277/480v using NM today.

If you have 2 legs that measure 120 volts to ground and one that measure 208 volts to ground the voltage between the legs will be 240 volts not 208 volts. This is a delta system.

If there is 208 volts between each of the legs then all 3 will measure 120 volts to ground. This is a wye system.

The 208 volt leg on the delta system is only used for 3 phase loads.

Curt

anyone ever seen an application where 277/480v was used, using NM? "

I have seen it used ..and we ripped every bit of it out. It was in a HUGE warehouse rite outside of Philly. The place had a drop ceiling with 2 x 4 layins. well over 300 of them. Somebody wired them all with romex, 12-4 romex to j-boxes then three 12-2s to a group of 8 or 10 fixtures. All the J-boxes and wire was just laying on the ceiling tiles and grid. J-boxs were nasty .. lose wire nuts, bare wires... What a mess ... spent weeks in the place re-wiring. In Lots of Places in PA ..ANYONE with insurance can be an electrical contractor, and it shows with some of the work I have seen there in the past 20 years.

caselec, forgot, your right about the 240v between phases on a wild leg system.
But still not sure what that 208v wild leg is doing on the 3 phase motors?

Motors don’t know that the wild leg is 208 volts to ground. Three phase motors don’t require a neutral. All they see is 240 volts between each of the legs.

Curt

caselec, I realize all that, but what is the 208v to ground (wild leg) used for usually?

Can't happen. Not in one system.

The first scenario (2 x 120v and 1 x 208) is a center-tap-grounded Delta or open-Delta, period. 240 line-to-line, and don't use the high leg (208v) for line-to-neutral loads.

The second (3 x 120v) will be a 208v hot-to-hot Y system, period. All three hots will measure the same to neutral (and thus, to ground).

The third hot wire for 3-phase loads, and never for line-to-neutral loads, period.

Larry Fine,
Not sure I'm getting it... so the wild (208v) leg never gets used to neutral, what is it there for then? Doesn't seem like it would do anything on a 3 phase motor if your measuring 240v between each phase.