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Joined: Jul 2004
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You also have to be careful using single phase 240v loads across the red leg if this is an "open vee" using 2 transformers. It can drag the open phase down and create an imbalance. You can end up with different voltages across the 3 legs. Single phase loads should only be on the centertapped trnsformer. The red leg is only for 3 phase loads.
Greg Fretwell
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Do they(manufacturers), or have they, ever made a 240V rated single pole breaker?
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EASports is correct, 240 single phase would be two phases connected to a two pole breaker, it would not matter which two phases are used even in a center grounded Delta.
The High leg is only a High Leg in reference to ground, not phase to phase.
I think the confusion is the difference between "single Pole" and "Single Phase"
Roger
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Roger- You blew it on this one. Look in the 2006 UL White book under "Molded Case Circuit Breaker Marking Guide" in the back of the book on p. 13. This agrees with 240.85. The lower of the two voltages on a Slant-Rated breaker can not be exceeded when measured to ground from either of the 2 phases involved.
[This message has been edited by George Little (edited 11-01-2006).]
George Little
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George, Roger- You blew it on this one. I was waiting for that. ![[Linked Image]](https://www.electrical-contractor.net/ubb/wink.gif) The problem I have with 240.85 is the wording "Solidly Grounded Circuit. A circuit breaker with a slash rating, such as 120/240V or 480Y/277V, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed the lower of the two values of the circuit breaker's voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the circuit breaker's voltage rating. A phase to phase circuit is not "Solidly Grounded" is it? The system may be grounded but the circuit isn't, so there is nothing prohibiting us from using a slash rated breaker on a phase to phase circuit using the high leg for one side of this ungrounded circuit. Roger [This message has been edited by Roger (edited 11-01-2006).]
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Not convinced your correct yet Roger- Sorry Here's the words out of the UL White Book. 3. Voltage Rating — All circuit breakers are marked with a voltage rating, including: 60, 125, 125/
250, 160, 250, 500 and 600 volts for dc; and 120, 120/240, 240, 277, 347, 480Y/277, 480, 600Y/347
and 600 volts for ac. If the voltage rating does not include the words “ac” or “dc,” the breaker is rated
for both ac and dc voltages. For ac voltage ratings other than 60 Hz, the frequency is marked.
Circuit breakers for use in Communications Equipment may also carry ratings of 30, 65 or 80 Volts dc.
Two-pole independent-trip breakers and single-pole breakers with handle ties that are rated 120/240 V
ac have been investigated for use in line-to-line single-phase circuits or line-to-line lighting and appliance
branch circuits connected to 3-phase, 4-wire systems, provided the systems have a grounded
neutral and the voltage to ground does not exceed 120 V.
Two-pole independent-trip breakers and single-pole breakers with handle ties that are rated 125/250 V
dc have been investigated for use in line-to-line connected 3-wire dc circuits supplied from a system
with a grounded neutral, where the voltage to ground does not exceed 125 V.
Two-pole independent-trip breakers and single-pole breakers with handle ties that are rated 125/250 V
(both ac and dc) have been investigated for use in accordance with either of the above two paragraphs,
as applicable.
Two- and three-pole common-trip breakers rated 120/240V ac are intended for use on 1-phase, 3-wire
circuits, where the voltage to ground does not exceed 120 V.
Two- and three-pole common-trip breakers rated 125/250 V or 125/250 V dc are intended for use on
1-phase and dc, 3-wire circuits, where the voltage to ground does not exceed 125 V.
Circuit breakers with a single voltage rating are intended for use in circuits where the circuit voltage
and the voltage to ground do not exceed the voltage rating of the breaker.
“Slant-rated” breakers with a rating such as 480Y/277 V are intended for use in circuits where the
circuit voltage does not exceed the higher of the two voltages and the voltage to ground does not exceed
the lower of the two voltages.
Based on the preceding paragraphs, “slant-rated” breakers (120/240, 480Y/277 V, etc., as opposed to
240, 480 V, etc.) are not intended for use on “slant-rated” delta systems. For example, a 3-pole, 120/240
V breaker is not intended for use on a 240/120 V, 3-phase, 4-wire, delta system, because on the high leg,
the voltage to neutral is 208 V. In this instance, a 3-pole, 240 V breaker should be used. Check it out and if I'm wrong- I'm a big boy and will have to rethink my understanding.
George Little
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George, Check it out and if I'm wrong- I'm a big boy and will have to rethink my understanding I don't think you're wrong nor do I think I'm wrong. (and no I'm not a politician ) As I said before, because of the wording, 240.85 can't be cited if the circuit itself is not a "slant" rated circuit such as a 120/240V dryer or a range, a straight 240 volt circuit is not grounded. The UL wording is also talking about circuits until the last paragraph, but even this paragraph starts off with "Based on the preceding paragraphs" which were talking about "Grounded Circuits" and "Voltage to Ground" IMO the violation would have to be 110.3(B) if the manufacturers information said it can not be done, and I know some do, but 240.85 needs some changing to be used. Roger
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Roger- I do understand your perspective on the issue and the wording is murky at best in the NEC. I would also admit that about 99% of the inspectiors I know, wouldn't even check for this violation. We had a UL rep at one of our IAEI seminars that went into great depth on the issue otherwise I'd not be aware of it. Thanks for the give and take on this one.
George Little
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This is the same trouble people get in when they are using two pole breakers on corner delta. They have to be rated for full circuit voltage not 120/240
Greg Fretwell
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Thanks for the give and take on this one. And the same from me. Roger
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