3-pole circuit breaker voltage rating on single phase

On Thu, 14 Apr 2005 21:38:10 GMT Michael A. Terrell wrote: | snipped-for-privacy@ipal.net wrote: |> |> The breaker would be wired like this: |> |> A N B G |> | | | | |> *-----------* | | |> | | | | | |> | +--|--+--|--+--|--+ | |> | | | | | | | | | |> | | ( | ( | ( | | |> | | | | | | | | | |> | +--|--+--|--+--|--+ | |> | | | | | |> *-----------* | | |> | | | | |> a n b g |> |> scanerio 1 scenario 2 scenario 3 |> A-N = 120 volts 240 volts 480 volts |> N-B = 120 volts 240 volts 480 volts |> A-B = 240 volts 480 volts 960 volts | | | That is not only an illegal way to connect anything, its dangerous. | How do you propose to ground the third leg in a three phase panel? What | happens if a contact on A or C weld and ground is open?

That is not the diagram of a three phase panel. Where did you ever get such an idea.

If any contacts weld closed in any breaker on any system, you have a problem. This diagram does not increase the risk.

Suppose your electrical system has a bolted fault and the breaker is welded closed? What design would you have to mitigate that risk in any system?

Besides, ground won't be open in my diagram because it bypasses the breaker. But I guess you didn't see that.

| If you only need two phases to drive the load you HAVE to use a two | pole breaker to meet code. It doesn't matter what mind games you want | to play, and the insulation voltage rating for a breaker is per pole so | your question is meaningless.

You can use a 3-pole breaker to protect and disconnect a 2-wire load by uisng just 2 poles, as shown in my diagram. The only code restriction I have seen is when attached a 3-pole breaker to a 2-bus panel. This is not the case here.

Further, the code allows (and REQUIRES in some cases) the disconnection of the neutral.

Although that is a fine discription of a Circuit Breaker I think Phil should start taking that New brain drug "Infuseium" };-)

or forget pointless ventures.....

if aint broke why fix it

=AEoy

He's brain dead. Might as well put him in the troll can.

| You might want to look at the DC rating of these breakers. Some are | rated by Square D to handle over 500VDC in UPS service, in which the | DC system is ungrounded. Typically, the positive DC lead is broken | through two adjacent breaker poles in series while the negative DC | lead is broken through the third breaker pole. Merlin Gerin has an | IEC rating of 1000VDC on their Masterpact brekaer.

Supposedly having the poles in series will increase the effective total voltage withstand, especially with respect to breaking the arc. And that is especially important for DC given no zero crossover to help extinguish the arc.

But I'm just wondering about the AC aspect. If a single pole can handle 480 volts on its own, then wouldn't two poles in series be able to handle 960 volts together? At least with single phase, the zero crossings happen at the same time.

So if we have line A coming in through pole A then to the load, and back from the load is line B back through pole C (not B), we have

960 volts going through 2 poles. This is an Edison style split single phase supply, but at 480/960 volts (I picked this level as there are common breakers for 480 and not for 960 specifically).

Suppose there is a fault to ground in line A. The breaker will open due to the current surge, and an arc forms across the contacts as pole A opens. But this is a 480 volt arc, fully within the capability of the breaker to interrupt and extinguish the arc at least by the next zero crossing.

Now suppose there is a fault between line A and line B. This is a fault across 960 volts. But this fault also is going through two poles opening at the same time. So the voltage should be split across the two arcs. The question here at this point is: does the wiring of 2 poles in series really work like that, and for AC? Is this the theory that should apply for the arc issues?

Then there is the breaker case dielectric issue. Obviously it should be able to withstand 480 volts to ground, so one layer of the dielectric would have that rating. If there were two such layers between adjacent poles, that should give them a higher withstand capability. Would it be the 960 volts? But since these breakers are a single unit design, I can imaging that only one layer of dielectric wall exists between adjacent arc chambers. So that's why I am wondering about the voltage withstand specifically between the far poles of A and C, where B would be (held if necessary) at a potential half way between (that would be

480 volts relative to either side if 960 is applied to A and C). Since it is an Edison style single phase system, the middle pole can be held at ground potential, and thus no more than 480 volts to either of the other poles, by connecting both its in and out lugs to neutral (this is not implying that it switches the neutral ... just connect both of them to the solid neutral bar).

| Regards, | Chris Johnston | |>Consider a 3-pole circuit breaker with the pole sections side by side |>so that pole 1 and pole 3 have pole 2 in the middle. This is a very |>typical circuit breaker design for molded case breakers from companies |>like Cutler-Hammer and Square-D. These typically have a voltage rating |>giving a single number, and suitable for that voltage line to line and |>relative to ground. For example a 480 volt rating would allow use in |>a 480Y/277 volt WYE system, as well as a 480 volt corner grounded delta |>system. These breakers typically have ampere ratings as high as 1200. |>This would be in contrast to typical miniature branch breakers that have |>a dual voltage rating, one for line to ground and the other for line to |>line, such as 120/240 or 480/277. |>

|>Here's what I want to learn more about. Presumably these breakers |>might not have any greater line to line voltage rating than line to |>ground because they may be constructed with no extra insulation levels |>between the poles. The insulation between poles could very well be |>just the same as the insulation to the outside. This would contrast |>with placing two or three single pole breakers side by side where you |>would have double the insulation between poles, and some amount of |>greater voltage capability between them (perhaps). |>

|>What I want to focus on in a 3-pole molded case breaker is the voltage |>"endurance" capability (I'm avoiding the term "rating" here so as not |>to be confused with formal standard ratings such as UL, or manufacturer |>specifications that could incur legal liability) between the FAR poles, |>e.g. between pole 1 and pole 3 of a three pole breaker. Is there any |>reason there could not be an even higher voltage "endurance" between |>these far poles, as long as the middle pole in between does not have a |>relative voltage any greater than the formal rating? |>

|>Consider a 480 volt 3 pole breaker, such as Square-D model FAL34100 |>or others like it. It can be used on a 480 volt delta three phase |>power system. But what about a single phase system where there are |>two poles at 180 degrees phasing, with 480 volts relative to ground |>on each, e.g. a 480-0-480 system, with the middle pole connected to |>the grounded neutral wire of this system? Between pole 1 and pole 2 |>there would be 480 volts. Between pole 2 and pole 3 there would be |>480 volts. But between pole 1 and pole 3 there would be 960 volts! |>But these poles are well separated by the middle pole. |>

|>If that's a little high for you, then try a lower voltage breaker such |>as the QDL32100 (rated for 240 volts, including 240 delta) being used |>on a 240-0-240 single phase system connected as described, where it |>would see 480 volts between pole 1 and pole 3. |>

|>In what way could a breaker like that NOT have a voltage "endurance" |>capability of 960 volts between poles 1 and 3 when the middle pole is |>connected to the grounded conductor that has no more than 480 volts |>relative to either phase? |>

|>Please note that I am NOT asking about formal specification or rating. |>I'm NOT asking of such a connection would be in compliance with any |>electrical code, or if such a connection would be consistent with the |>purpose it is safety listed for. I am asking about the physics of the |>design, and any aspect of electricity that would make it not possible |>for a breaker to generally be capable of doing this. |>such systems are in common use. |

Phil-emon: I see what you mean:

To answer: The Bimetalic strip in a beaker can loose it's resilience to the target current/voltage limit (or flex response to temp>) with time but none of this is mentioned in books or mfgr's specs.that i am familiar with.

I think when the Bimetalic strip starts to wear out it's heat sensing characteristic the darn thing starts tripipng over nothing and then comes the time it just doesn't reset: then you throw it out and replace it with a new or functioning one.

It can fail due to Bimetalic Strength Failure does that answer your question.

=AEoy

| Phil-emon: I see what you mean: | | To answer: The Bimetalic strip in a beaker can loose it's resilience to | the target current/voltage limit (or flex response to temp>) with time | but none of this is mentioned in books or mfgr's specs.that i am | familiar with. | | I think when the Bimetalic strip starts to wear out it's heat sensing | characteristic the darn thing starts tripipng over nothing and then | comes the time it just doesn't reset: then you throw it out and replace | it with a new or functioning one. | | It can fail due to Bimetalic Strength Failure does that answer your | question.

How is this a failure mode that is specific to L-L voltage on breakers at the 480/960 level, and not at the 120/240 level (which do exist)? Or how is this a failure mode that is specific to voltage. If a breaker can fail (and it can, and many do) then it can fail in many circumstances and cause these same problems.

The heat dissipation in the breaker is a function of current since it is a very low impedance in the circuit. The voltage drop across the strip is going to be a function of its resistance and current flowing through. Change the supply voltage, and adjust the load to use the same current at the new supply voltage, and the bimetal strip will still get the same current and as long as it has the same resistance, get the same wattage and the same heat.

But of course there are many way it can change. Years of hot operation can loosen or change its mounting points. Or it's metallurgy can change in some way and it no longer flexes the same way. Or the ability of the breaker case to dissipate heat can be reduced (insects crawling into the little holes and plugging them up). But all of these problems exist in any case. They would not be specific to a breaker running double the L-N voltage on the A-to-C poles.

Phil: you are not going to let this rest are you???

what you're saying seems to point to magnetic interference from chambers A-C to the extent of causing the anomaly you've described.

=AEoy

| Phil: you are not going to let this rest are you???

Roy: you are never going to address what I ask are you???

| what you're saying seems to point to magnetic interference from chambers | A-C to the extent of causing the anomaly you've described.

I do not see how you draw such a conclusion out of what I am saying. And if that were true, it would negate being able to use a 2-pole breaker as is commonly found in distributed bus phasing panels (for either single or three phase). But in fact there are plenty of breakers with adjacent chambers in which magnetic interference could occur. So it really seems that this is a non-issue.

If you want me to put it to rest, then due to a total lack of any technical evidence put forth to the contrary, I would have to conclude that voltage withstand between pole A and pole C of a three pole breaker constructed with the poles laid out in a linear fashion (as virtually all of them are) will be about twice that of the voltage withstand between adjacent poles.

I take it, Roy, that you do not, and never have, designed circuit breakers for a living, or else if you do, you are under an NDA from divulging any technical info about any circuit breakers whatsoever.

From: snipped-for-privacy@ipal.net On Fri, 15 Apr 2005 13:35:55 -0400 Roy Q.T. wrote: | Phil: you are not going to let this rest are you??? Roy: you are never going to address what I ask are you??? | what you're saying seems to point to magnetic interference from chambers | A-C to the extent of causing the anomaly you've described. I do not see how you draw such a conclusion out of what I am saying. And if that were true, it would negate being able to use a 2-pole breaker as is commonly found in distributed bus phasing panels (for either single or three phase). But in fact there are plenty of breakers with adjacent chambers in which magnetic interference could occur. So it really seems that this is a non-issue. If you want me to put it to rest, then due to a total lack of any technical evidence put forth to the contrary, I would have to conclude that voltage withstand between pole A and pole C of a three pole breaker constructed with the poles laid out in a linear fashion (as virtually all of them are) will be about twice that of the voltage withstand between adjacent poles. I take it, Roy, that you do not, and never have, designed circuit breakers for a living, or else if you do, you are under an NDA from divulging any technical info about any circuit breakers whatsoever.

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---------------------------------------------- I have done nothing but pick the living daylight off those beaker characteristics with you., No, and I will be presuming the doubled voltage withstanding between said poles in HV=3D panels =3D(from whence yo= u reference) until & if i encounter the contrary myself. * Besides every time i address your query you change to a different Angle in your Hypothesis. =AEoy

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If he was serious about design issues he would be contacting the engineering departments of Square D, or other manufacturers of Circuit breakers.

| If he was serious about design issues he would be contacting the | engineering departments of Square D, or other manufacturers of Circuit | breakers.

Actually I did a few months ago. I spoke with one engineer who said "as long as the line to ground voltage does not exceed XXX volts, it will be fine". I asked for more details but that was denied for trade secret reasons. The manufacturers will not be forthcoming for many legal reasons. Since I'm not going to be buying their products, they have no reason to deal with me any further. If I were in the market for them, as opposed to just in the learning process, maybe they would. It could well be that if I had an application for using a breaker on a single phase

480/960 volt Edison configuration power source, they could recommend using a 480 volt 3-pole breaker as I had previously suggested. Or maybe they would have to tweak something in the design or manufacture of the breaker. Or maybe they would have to start all over and make a specific 960 volt model. I sensed that engineer did know what he needed to know to figure it out; he just wasn't allowed to tell me. I also sense that almost everyone who has replied in this thread doesn't know what they are talking about. Of course I'm no expert, but I suspect I could accidentally stumble on the correct theory and you guys wouldn't recognize it at all. Maybe I already have and it offends some that I did so.

It is the design of the contacts and the surrounding area, and the ability to quench an arc as they open at the rated voltage and short-circuit current. For example, a medium voltage breaker construction is different from low voltage devices for use at 600V or less.

Ben Miller

The breaker may very well be capable of doing what you suggest. Remember that you need to allow for unequal voltage division, as one pole may see more than half of the 960 volts if there is a line-line fault.

The real issue is that nobody (ie. UL) has tested and rated it under these conditions. The manufacturer would need to pay for this, and it is not an application that they need to be concerned with.

Ben Miller

| The breaker may very well be capable of doing what you suggest. Remember | that you need to allow for unequal voltage division, as one pole may see | more than half of the 960 volts if there is a line-line fault.

That would also be an issue on 120/240 volt single phase circuits with the

120 volt L-N rated breakers. But they are rated for 240 volt L-L in 2-pole versions, so they clearly have the capability in those models. But from what I can tell, the 2-pole models are essentially the same atwo 1-pole models stuck together and using a common handle tie (internally or externally). Is there something in the design above and beyond what makes it a 120 volt L-N breaker that can make it do 240 volts L-L with 2 breakers?

| The real issue is that nobody (ie. UL) has tested and rated it under these | conditions. The manufacturer would need to pay for this, and it is not an | application that they need to be concerned with.

That's one of the general difficulties with these listings. Instead of doing them in a generalized way (e.g. specify the maximum rating in all aspects, rather than just one that the market most commonly uses), they are done in a most narrow way. That's probably to keep testing costs low (e.g. test at a specified parameter for consistent performance). At all voltages below 347 volts L-N every breaker I see has a L-L rating at least as much as you really would get from 3-phase power at those voltage combinations. There being a gap of common usage of voltages between 600 volts and 2400 volts, you pretty much don't see anything there. This is really what I have suspected all along.

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----------------------------------------------------------------------------- | Phil Howard KA9WGN |

| | (first name) at ipal.net | |

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|> Here's another way to phrase it. Let's suppose there are two different |> products, one being a 3-pole breaker suitable for 480 volt delta, and |> another 3-pole breaker suitable for 480/960 volt single phase under the |> stipulation that the B-pole be connected to (but not necessarily switch) |> the neutral conductor (e.g. the neutral can pass around it as well). |> So with these 2 breakers, what would be different? Or how hard would |> it be to make one that can meet both requirements in the same unit? | | It is the design of the contacts and the surrounding area, and the ability | to quench an arc as they open at the rated voltage and short-circuit | current. For example, a medium voltage breaker construction is different | from low voltage devices for use at 600V or less.

Would that design need to change, over that of an X volt L-N 1-pole breaker to have it support 2X volts L-L in a 2-pole breaker?