480/277V Rated Breakers on a Delta System

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fifty60

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USA
I have some 3 pole breakers that are 480/277V rated. Is it ok to wire these up on a delta supply, or do I have to have a Y supply? I would think that the 480/277V rating would not affect in any way them being connected to a Delta system.

I would think that If they were not slash rated, then I could not connect them up as 277V Y, but not the other way around. The 480V is phase to phase regardless right?
 

rlundsrud

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Location
chicago, il, USA
Since there isn't a code requirement for which phase the high leg is on, the breaker would have to be designed to handle the 480 volts phase to phase regardless of which of the phases the high leg was on. Given that bit of logic I would say yes, but that is an unqualified statement. When it comes down to it the manufacturer is who you would need to contact so you can verify that it is designed for that purpose.

Bob
 

JoeStillman

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West Chester, PA
It looks like you will need to be sure you know whether the transformer is delta connected on the secondary or wye connected, but feeding no neutral wires. Lot's of 3-wire 480V systems are fed from wye connected transformers. Just because its only 3 wires doesn't necessarily mean it is a delta system.

A grounded or ungrounded delta secondary can have a voltage of 480V to ground, and that would exceed the rating of your slash-rated 480/277V breaker.
 

don_resqcapt19

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I think 240.85 is pretty clear as to the application of slash rated breakers.
240.85 A circuit breaker with a straight voltage rating, such as 240 V or 480V, shall be permitted to be applied in a circuit in which the nominal voltage between any two conductors does not exceed the circuit breaker?s voltage rating. A two-pole circuit breaker shall not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked 1??3? to indicate such suitability.

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.
 

don_resqcapt19

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Why are all 3 phase breakers straight rated? Is that why they cost so much?
They are not all straight rated. A quick look at one manufacturer's on line catalog showed a number of 3 phase breakers with 208Y/120, 480Y/277 and 600Y/347 ratings.
 
Hi, all.

Sorry for coming late to this subject, but I was searching for some related information and found this in the process. I question the apparent conclusion of this thread, specifically, the reference to Mike Holt's article on ECMWeb.

In that article, the money-quote supposedly is this:

Two-pole breakers can be either slash or straight voltage-rated, whereas 3-pole breakers are all straight voltage-rated.

Now, I first notice that this is a very dated article as it was posted on 1 November 2001, and it referred to NEC 2002. The age of this article may not be the most important factor to consider, but neither should it be dismissed. In any case, much as I appreciate Mike Holt's writing, education, and service to this community, if I ever have to defend a code-related design/wiring choice that I make, I don't figure claiming that "Mike Holt said it will be OK" is going to be a successful argument.

More to the point, I wonder if Mike had molded-case circuit breakers in mind. (Fair disclosure, I have only been involved with industrial controls since 2003, and so I surely lack a depth of involvement in the history.) In my admittedly limited experience, I don't know that I have ever personally laid eyes on a slash-rated, 3-phase MCCB. However, sitting in my lap at this moment is a 2013 ABB Industrial Controls catalog which does offer slash-rated MCCBs, though they certainly are a minority in comparison to the straight-rated breakers. I wonder if these were available 14 years ago when the ECMWeb article was first written. Nevertheless, don_resqcapt19 was correct in stating that, today, 3-phase, slash-rated MCCBs are available.

I am also conscious that when we speak of circuit breakers, we might be talking about molded-case circuit breakers, or we might be talking about miniature circuit breakers (MCBs). The original post was not clear on this point. In MCBs, I do find straight-rated, 3-phase devices for up to 240VAC. However, if I want an MCB rated for 480V, I have so far found only slash-rated MCBs (480Y/277VAC). Perhaps I've just not looked in the right place yet, but I suspect that the code writers have a sound electronic physics reason for allowing MCBs at 480V to only be slash rated, something maybe having to do with the neutral's solid grounding in a wye system. This is in fact was NEC 240.85 (2014) seems to suggest (see the second paragraph of what don_resqcapt19 quoted). The informational note in the same section of the NEC on this point also appears to suggest that a corner-grounded delta system is not considered solidly grounded:

Informational Note: Proper application of molded case circuit breakers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the circuit breakers? individual pole interrupting capability.

For what it is worth,
Shack
 

GoldDigger

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All that quote says is that a corner grounded delta is not a solidly grounded wye.
Use of a slash rated breaker on a corner grounded delta is not ruled out by it not being solidly grounded but by the voltage to ground on the two ungrounded wires being greater than the second number in the rating.
Also note the one can use a slash rated breaker on a corner grounded 240 delta, it just has to be a 480/277 rated breaker. :)
 
You are right, GoldDigger.

I was in error when I stated that the note suggested a corner-grounded delta is not solidly grounded. As you say, it is simply not solidly-grounded wye.

Also, your point about using a 480/277 rated breaker on a corner grounded 240 delta system is also helpful in answering the original post. I had assumed that fifty60 was proposing connection of a slash-rated breaker to a 480-delta system, but reviewing what was actually written, this was not stated. I guess that he should be OK if the power system is 277 or less, line-to-line.

Standing corrected :),
Shack
 

Jraef

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Good observation.

Yes, you will not find any of the MCB style breakers that are not slash rated for 480V. That's because they are all really IEC design devices, and nobody in the world uses delta power systems besides us in North America, so they don't design for it. Likewise many of the newer design lowest cost Molded Case breakers are also slash rated for the same reason; the way they can make them cheaper is to have very high volumes, and that means global markets where delta ratings buy you nothing but cost on the construction side.

The reason for the added cost is the reality of a Wye system; an asymmetrical fault, meaning one pole goes to ground, is the most destructive in terms of mechanical energy. If you have a bolted fault (phase to phase), the mechanical (magnetic) forces created by the energy flowing to the fault is split between at least two poles, so each pole has to handle at worst 1/2 of the forces created by the fault. In a grounded (asymmetrical) fault, all the mechanical force is on the one pole. So then if you have a delta supply where the line to ground potential is 480V, there will be a lot more kVA flowing to ground and therefore a lot more mechanical force, so the parts must be significantly stronger to keep from becoming shrapnel. If you have a wye system, the voltage to ground is 58% of the line voltage, so 58% of the kVA and mechanical force, meaning smaller cheaper lighter parts to make the breakers.

But if you are a breaker manufacturer selling those smaller cheaper lighter breakers to a world in which delta power systems only exist in one corner of it, you tell the people in those corners, "just deal with it".

That's us...
 

mbrooke

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Thanks JRaef for the info, that makes sense now:)


And, I think for once in history, Mike Holt might be wrong :eek: IS that even possible? :blink:
 
Thank you, Jraef, for your explanation of the electrical reasons at play in the slash ratings of the MCBs. I do appreciate it as it provides the information I was seeking when I stumbled onto this thread.

I suppose that the spacing between the poles on a miniature circuit breaker also come into play, viz. with only 18 mm between each pole, the voltage can only go so high before more exotic (and expensive) materials must be involved to prevent a breakdown of the CB's insulation in a fault event. This amounts to greater cost, just as you mentioned. Another way around this problem is to design more space between the poles, but then the MCB no longer fits the standard IEC size profile.

By way of a somewhat related rabbit-trail, I just looked at a circuit breaker for motor protection (not a miniature CB) that has UL certification both as a manual motor controller and as a Type E combination motor controller. Now, the interesting thing to me about this is that as a manual motor controller, the device has straight-voltage certification up to 600VAC. However, as a Type E combo controller, the device has only slash-rating certification involving 480 and 600VAC. (At 240VAC, it is still straight-rated.) I know that UL is not the same as NEC, but it is interesting to me that the motor protector has different certifications depending on the usage.


mbrooke, within the category which Mike was probably addressing, he might have been entirely correct at the time. Over the dozen+ years in the interim, though, one or two things might have changed.:)

Very finest regards,
Shack
 

Jraef

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Thank you, Jraef, for your explanation of the electrical reasons at play in the slash ratings of the MCBs. I do appreciate it as it provides the information I was seeking when I stumbled onto this thread.

I suppose that the spacing between the poles on a miniature circuit breaker also come into play, viz. with only 18 mm between each pole, the voltage can only go so high before more exotic (and expensive) materials must be involved to prevent a breakdown of the CB's insulation in a fault event. This amounts to greater cost, just as you mentioned. Another way around this problem is to design more space between the poles, but then the MCB no longer fits the standard IEC size profile.

By way of a somewhat related rabbit-trail, I just looked at a circuit breaker for motor protection (not a miniature CB) that has UL certification both as a manual motor controller and as a Type E combination motor controller. Now, the interesting thing to me about this is that as a manual motor controller, the device has straight-voltage certification up to 600VAC. However, as a Type E combo controller, the device has only slash-rating certification involving 480 and 600VAC. (At 240VAC, it is still straight-rated.) I know that UL is not the same as NEC, but it is interesting to me that the motor protector has different certifications depending on the usage.


mbrooke, within the category which Mike was probably addressing, he might have been entirely correct at the time. Over the dozen+ years in the interim, though, one or two things might have changed.:)

Very finest regards,
Shack
As a manual motor starter, it is not expected to be the Branch Short Circuit and Ground Fault Protection Device, it would be used down stream of another one somewhere. As a Type 2 controller, it must act as the branch SCPD and therefore will be expected to survive the act of interrupting the fault (within the stated limitations).

I too feel that the issue with the Mike Holt statement is just because of age. Slash rated breakers have only recently become an issue as more and more of the small cheap MCBs became rated for 480V. Before that, they were limited to 230V applications in North America, even though they had higher ratings per IEC standards. Most had only UL1077 listings as "supplemental protection" (if anything), which, just like the above issue, meant that they had to have another SCPD ahead of them. What changed was that somewhere around 2004-2005 several of the mfrs went after UL489 listings as stand-alone circuit breakers, but could not hold up to the rigors of delta power systems asymmetrical fault forces, leaving them with the 480/277V ratings, and UL changed their rules to allow it, as long as they were not misused. Once that became somewhat acceptable, some of the other mfrs then started doing the same on their MCCBs as well, which began to muddy the water. This then resulted in forcing the NEC to try to make it clearer, I think in the 2005 code. I was working for Siemens at the time, it was a mess because a number of the bottom feeder players were not properly understanding the issues and selling them willy-nilly as "cheaper" breakers, which lead to contractors and OEMs getting into trouble in the field. Still happens actually, but not as much.

PS: spacing between the poles is also an issue as well, but many were able to overcome that by adding barriers between the poles that must be installed in the field after connecting the conductors. They just make a simple little dovetail slot in the frame and the barriers slide in. Here's an example (on the left).
insulation-barriers-air-circuit-breaker.gif
That doesn't fix the other issues however.
 
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mbrooke

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As a manual motor starter, it is not expected to be the Branch Short Circuit and Ground Fault Protection Device, it would be used down stream of another one somewhere. As a Type 2 controller, it must act as the branch SCPD and therefore will be expected to survive the act of interrupting the fault (within the stated limitations).

I too feel that the issue with the Mike Holt statement is just because of age. Slash rated breakers have only recently become an issue as more and more of the small cheap MCBs became rated for 480V. Before that, they were limited to 230V applications in North America, even though they had higher ratings per IEC standards. Most had only UL1077 listings as "supplemental protection" (if anything), which, just like the above issue, meant that they had to have another SCPD ahead of them. What changed was that somewhere around 2004-2005 several of the mfrs went after UL489 listings as stand-alone circuit breakers, but could not hold up to the rigors of delta power systems asymmetrical fault forces, leaving them with the 480/277V ratings, and UL changed their rules to allow it, as long as they were not misused. Once that became somewhat acceptable, some of the other mfrs then started doing the same on their MCCBs as well, which began to muddy the water. This then resulted in forcing the NEC to try to make it clearer, I think in the 2005 code. I was working for Siemens at the time, it was a mess because a number of the bottom feeder players were not properly understanding the issues and selling them willy-nilly as "cheaper" breakers, which lead to contractors and OEMs getting into trouble in the field. Still happens actually, but not as much.

PS: spacing between the poles is also an issue as well, but many were able to overcome that by adding barriers between the poles that must be installed in the field after connecting the conductors. They just make a simple little dovetail slot in the frame and the barriers slide in. Here's an example (on the left).
View attachment 11687
That doesn't fix the other issues however.


Never thought of it that way. But my question is, why are most 240 volt 3 phase breakers straight rated but not double poles. Would this account for the price difference between a 3 phase 3 pole vs a 2 pole breaker?
 

Jraef

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Never thought of it that way. But my question is, why are most 240 volt 3 phase breakers straight rated but not double poles. Would this account for the price difference between a 3 phase 3 pole vs a 2 pole breaker?
It's only because there is a feature on the slots for B phase on a 120/240 delta panel so that 1 and 2 pole slash rated breaker frames cannot plug into the B phase, and that for the 2 pole that are delta rated they have a feature that allows them to be plugged in anywhere. But then you will notice that the IC rating will be at 10kAIC only, no option for 22kAIC or 65kAIC, because you won't find a 4 wire delta service big enough to need that. Then at 3 pole, that is no longer an issue so they can be plugged in anywhere already, plus then you CAN get a larger delta service, so you need the higher IC ratings available. Basically it's just a market issue; they don't make higher IC delta rated 2 pole breakers because nobody would ever need them.
 

mbrooke

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It's only because there is a feature on the slots for B phase on a 120/240 delta panel so that 1 and 2 pole slash rated breaker frames cannot plug into the B phase, and that for the 2 pole that are delta rated they have a feature that allows them to be plugged in anywhere. But then you will notice that the IC rating will be at 10kAIC only, no option for 22kAIC or 65kAIC, because you won't find a 4 wire delta service big enough to need that. Then at 3 pole, that is no longer an issue so they can be plugged in anywhere already, plus then you CAN get a larger delta service, so you need the higher IC ratings available. Basically it's just a market issue; they don't make higher IC delta rated 2 pole breakers because nobody would ever need them.

But why not offer a section of 120/208Y 3 pole breakers rather than having them always be 240 volts? I have feeling that the 240 volt version are actually designed with a much higher AIC so when applied to a delta high leg the AIC is 10ka.
 

templdl

Senior Member
Location
Wisconsin
I have some 3 pole breakers that are 480/277V rated. Is it ok to wire these up on a delta supply, or do I have to have a Y supply? I would think that the 480/277V rating would not affect in any way them being connected to a Delta system.

I would think that If they were not slash rated, then I could not connect them up as 277V Y, but not the other way around. The 480V is phase to phase regardless right?
It is the voltage to ground that is the issue. 277v doesn't qualify as the voltage to ground is 480v. A straight 480 or 600v rated breaker does.
 
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