Just make the high leg smaller.

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chris kennedy

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
I'm having an issue with the shop. I have a system designed as 208y/120. Now POCO is giving me 120/240 delta. (another long story) All the gear is mounted and has main breakers. Time to start shopping wire.

Soooo, the owner of our company says he will size the high leg 2 sizes smaller than the other ungrounded conductors. I say you cant do that the gear has main breakers. He tells me that won't make a difference since the high leg has higher voltage therefore smaller wire will carry higher amperage.












???:confused::mad:

I continue that if you want to use a smaller high leg you calculate the load on it and fuse accordingly. I am told you are allowed 2 sizes smaller even with a breaker, and another guy at the shop agrees with him.

So I'm banging my head here looking for the article/section that allows this.

I know I'm right but a little brain dead tonight. Little help please.
 
230.90(A) Ungrounded Conductor. Such protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor. A set of fuses shall be considered all the fuses required to protect all the ungrounded conductors of a circuit. Single-pole circuit breakers, grouped in accordance with 230.71(B), shall be considered as one protective device.
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that should do it;)

I't not a grounded conductor, it is a ungrounded conductor!
 
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Thanks Hurk, should have mentioned these are the load side of the mains, feeders, not that I believe it makes any difference.
 
chris kennedy said:
Soooo, the owner of our company says he will size the high leg 2 sizes smaller than the other ungrounded conductors. I say you cant do that the gear has main breakers. He tells me that won't make a difference since the high leg has higher voltage therefore smaller wire will carry higher amperage.
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That's pretty weird. Has your boss followed this practice in the past with high leg services or is this his first one??:confused:

Have you told him he can't use the slash rated breakers on the high leg yet?(120/240)
 
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Cow said:
That's pretty weird. Has your boss followed this practice in the past with high leg services or is this his first one??:confused:
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In business for 38 years. I just don't think he gets the fact that I have breakers.

Have you told him he can't use the slash rated breakers on the high leg yet?(120/240)
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Not an issue, panels are almost empty, I can move them around. This is a build-out for future tenant space.
 
Soooo, the owner of our company says he will size the high leg 2 sizes smaller than the other ungrounded conductors. I say you cant do that the gear has main breakers. He tells me that won't make a difference since the high leg has higher voltage therefore smaller wire will carry higher amperage.

I think what he probably meant to say was that since the voltage was higher on that conductor that the amperage would be less, therefore allowing a smaller conductor to carry the lesser amperage.
 
jap said:
Soooo, the owner of our company says he will size the high leg 2 sizes smaller than the other ungrounded conductors. I say you cant do that the gear has main breakers. He tells me that won't make a difference since the high leg has higher voltage therefore smaller wire will carry higher amperage.

I think what he probably meant to say was that since the voltage was higher on that conductor that the amperage would be less, therefore allowing a smaller conductor to carry the lesser amperage.
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Doesn't matter still against code 230.90(A)
 
jap said:
Soooo, the owner of our company says he will size the high leg 2 sizes smaller than the other ungrounded conductors. I say you cant do that the gear has main breakers. He tells me that won't make a difference since the high leg has higher voltage therefore smaller wire will carry higher amperage.
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Smaller wire will carry higher amperage that makes no sense at all I hope he gets it inspected.
 
jap said:
I think what he probably meant to say was that since the voltage was higher on that conductor that the amperage would be less, therefore allowing a smaller conductor to carry the lesser amperage.
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What he should have said is that the higher voltage could allow the smaller conductor to provide the same amount of power.

The problem with his illogic is that the current only matters to the conductor, and the voltage only matters to the insulation. The OCP must still be sized to protect the wire.

I have used smaller high-leg conductors, but they were only subject to the 3-phase portion of the load, and were properly protected.
 
FWIW, my wire was delivered the next day and was sized accordingly. You would have to meet Joe to know how I struggle. He doesn't even own an 08 NEC yet. But he is one heck of a business man.:)
 
There are two ways to size the grounded conductor for the service.

250.24(C)(1) Routing and Sizing.
This section may allow for even smaller than 2 sizes.

220.61 Feeder or Service Neutral Load.



But the high leg your boss is talking about is not a grounded conductor. I am assuming the delta service you are speaking of is a 4-wire delta, midspan tap delta system.
The high leg is an ungrounded conductor, and the voltage that is high is to ground, not phase to phase. there is no allowance to permit a smaller size conductor due to voltage.

I mention a 4-wire delta system, as you said there is a high leg.
 
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