Red leg Questions

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bure961

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Farmingham, MA
On /240 3 phase 4 wire red leg where the b phase is 208 to neutral can that phase be used for a piece of equipment such as an ac unit rated single phase 230 volt ? Or any load 208-230v single phase safely ? Thanks for your repleys
 
You first need to find a single pole circuit breaker that is rated for more than 120 volts.
 
infinity said:
You first need to find a single pole circuit breaker that is rated for more than 120 volts.
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Wouldn't any 2- or 3-pole 240V straight-rated breaker (not 120/240 slash-rated) permit using the "B" phase for a 208V Line-to-Neutral circuit?

I do not recommend doing so, even if permitted.
 
bure961 said:
On /240 3 phase 4 wire red leg where the b phase is 208 to neutral can that phase be used for a piece of equipment such as an ac unit rated single phase 230 volt ? Or any load 208-230v single phase safely ? Thanks for your repleys
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Yes, you can supply line to line loads between the high leg and one of the other phases. Also though, you should not supply any equipment that requires a neutral such as a dryer, range, etc that will have internal line to neutral loads.The catch is that you must use straight 240 volt rated breakers not 120/240 rated.
One other thing to consider though is the way most POCOs design 120/240 open delta transformer banks. They typically build these for use where the need for 3 phase is minimal and as such expect to see most of the load on the non high leg. As a result, say for example, you had a whole building full of only 240 line to line loads and you balanced all these 2 pole circuits across all 3 phases you might overload the POCO transformer. Some POCOs even spell out in their terms of service that you can only use the high leg to supply 3 pole/3 phase loads. I don't think they have a high leg police :cool:department though so if as long as it is not overly abused they would never know.
 
Smart $ said:
Wouldn't any 2- or 3-pole 240V straight-rated breaker (not 120/240 slash-rated) permit using the "B" phase for a 208V Line-to-Neutral circuit?

I do not recommend doing so, even if permitted.
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I'm guessing that he wants to use a 1-pole breaker otherwise it kind of defeats the purpose of using the high leg for a 208 volt, 1Ø load.
 
infinity said:
You first need to find a single pole circuit breaker that is rated for more than 120 volts.
Click to expand...

I've never seen a single pole breaker that is straight rated for 240V or even 208V. Most are slash rated for 120/240V, which the 120V rating limits your phase to ground voltage. This is something to watch out for, on the 2-pole breakers in the same family. Some are straight and some are slash rated.

In practice, the only way I anticipate you being able to do this, is to use a 480V rated panelboard, whose breakers are by design rated for 277V to ground.

And even then, I don't immediately see the advantage of using the high leg-to-neutral. Most loads in this voltage class, are built for working with the line-to-line voltage of 240V, and will operate more efficiently with it. They carry a dual 208V rating for use in a WYE system.
 
high leg

high leg

Maybe I misunderstood the OP, but I took it as he wanted know if he could use the high leg to another phase to serve a single phase line to line load. But I agree that if he was meaning high leg to neutral to serve a 208/230 single phase load that would present a number of issues starting with the 1 pole breaker.
 
bure961 said:
i should have though about this a little more not realizing there is no cb for 208 single phase.
thanks again
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You could, but a standard 240/208/120 volt panel isn't going to utilize single pole CB's that can be used with 208 volts. As mentioned you could use a 480 volt panel with 277 volt single pole CB's but that would be quite a bit of over design to simply not use a 2 pole CB in the first place.
 
MD84 said:
Should it not be orange? See 110.15
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Indeed it should be orange, as orange is the NEC required color for the high leg conductors.

"Red leg" still sticks around as a trade slang name for it, even though it has nothing to do with the color red. At one point, it might've been the convention for it to be red, which wouldn't make sense in today's practices (red = B-phase on WYE). There also used to be a requirement to have the high leg be on the C-phase, even though now it is required to be on the B-phase. Some utilities may still require it on the C-phase in the meter due to legacy equipment, in which case a contractor has to migrate it to the B-phase by the time it reaches a panelboard.
 
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About 35 years into this trade and I would be surprised if I ran into one of these high leg systems more than once. Just not popular around here, I don't think they are even offered for services by the utilities.
 
Coincidently I've got an ongoing project, new boilers in a Steam Plant at a University that is a center grounded 120/240V system with the high leg identified red.


Roger
 
Carultch said:
What was the convention for a 120/208WYE system's color indicators, back when red was common for the high leg?
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The same, Black Red Blue, of course wiggy's were in every tool pouch, back pocket, or on the belt.

Roger
 
roger said:
The same, Black Red Blue, of course wiggy's were in every tool pouch, back pocket, or on the belt.

Roger
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WOW! That's gotta be confusing. So how would one tell the difference between a standard B-phase and a high leg? Besides the obvious, of measuring the voltages.

And what is a wiggy?
 
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