Are 3 pole breakers only for 3 phase?

[skorpioskorpio]

So there has been previous threads here and there asking if you can use a 3 phase breaker (and seemingly used interchangeably with 3 pole) in a single phase panel. However they all revolve around only using 1 or 2 poles of that breaker. My question is can you use a 3 pole breaker, to common trip 3 circuits? Not common neutral MWBCs, or just using 2 poles for a 240V circuit. I have machines that require 20A/240V AND 20A/120V on separate plugs, and if either trips I want it all to trip, so basically 2 poles for the 240V + 1 pole for the 120V. Can I do that and be NEC complaint? If it makes any difference we're talking Square D QO panels.

It is my understanding that it is not a violation to wire 2 120V circuits into a common trip 2 pole breaker, so I don't see why it would be a violation to wire a 240V + a 120V into a 3 pole breaker, or am I missing something? Prior threads seem to indicate that perhaps all 3 pole breakers were for 3 phase panels only, although the Square D data sheets for 3 pole breakers don't seem to make any mention of 3 phase at all, just that they are 3 pole.

 

[Dennis Alwon]

If the voltage of the breaker is rated for your voltage then I don't see an issue with it either

 

[skorpioskorpio]

Well, yea, I don't see where this would be an issue either, but apparently there is this little UL nugget that was in a thread from a dozen years ago:

UL Molded Case Circuit Breakers Marking Guide '07​

page 17​

33. 3-Pole - 1-Phase Rated - 3-pole circuit breakers are suitable for use on 3-phase systems only, unless marked to indicate use on 1-phase systems, such as, "For 1-phase connections, use two outside poles," or an equivalent statement. A 3-phase breaker used in place of a 2-pole breaker on a 3-phase system, such as a 2-pole breaker used in a branch circuit that is actually two legs of a 3-phase system, is acceptable without the 3-pole breaker being specifically marked.​

​

Which seems like some rule, just to be a rule. 3 poles and 3 phase only relate to each other in that the math works. I really don't see what would be specific about a 3 pole breaker that would make it only "suitable for use on 3-phase systems". It's a 3 pole common trip breaker, period, just as 2 pole common trip breaker is exactly that. The marking example used is also a? I mean if you used the 2 outside poles, on a single phase system, wouldn't that specifically not be a branch circuit? Just seems like nonsense.

 

[jim dungar]

All listed multi-pole breakers have been tested for the performance for all combinations of loading. A 3 pole breaker has been tested as a 1, 2, and 3 pole devices.

 

[jim dungar]

Well, yea, I don't see where this would be an issue either, but apparently there is this little UL nugget that was in a thread from a dozen years ago:

UL Molded Case Circuit Breakers Marking Guide '07​

page 17​

33. 3-Pole - 1-Phase Rated - 3-pole circuit breakers are suitable for use on 3-phase systems only, unless marked to indicate use on 1-phase systems, such as, "For 1-phase connections, use two outside poles," or an equivalent statement. A 3-phase breaker used in place of a 2-pole breaker on a 3-phase system, such as a 2-pole breaker used in a branch circuit that is actually two legs of a 3-phase system, is acceptable without the 3-pole breaker being specifically marked.​

​

Which seems like some rule, just to be a rule. 3 poles and 3 phase only relate to each other in that the math works. I really don't see what would be specific about a 3 pole breaker that would make it only "suitable for use on 3-phase systems". It's a 3 pole common trip breaker, period, just as 2 pole common trip breaker is exactly that. The marking example used is also a? I mean if you used the 2 outside poles, on a single phase system, wouldn't that specifically not be a branch circuit? Just seems like nonsense.

The only time I have seen this restriction is in regard to breakers being used on corner grounded (i.e. Grounded B phase) systems.

 

[skorpioskorpio]

All listed multi-pole breakers have been tested for the performance for all combinations of loading. A 3 pole breaker has been tested as a 1, 2, and 3 pole devices.

OK, well sounds like I am good then. It's a CNC machine BTW, the axis and electronics run on 120V and the Spindle on 240V (which then goes into a VFD), they are wired into a jbox with a 120V/20A duplex and a 240V/20A duplex. If the spindle trips and the electronics keep going, bad things could happen (head crash), and visa versa, but to a lesser degree. ...and not only that but since the box technically has 3 hots and a neutral in it, I'd prefer they trip together, and kill the whole run.

 

[Jraef]

OK, well sounds like I am good then. It's a CNC machine BTW, the axis and electronics run on 120V and the Spindle on 240V (which then goes into a VFD), they are wired into a jbox with a 120V/20A duplex and a 240V/20A duplex. If the spindle trips and the electronics keep going, bad things could happen (head crash), and visa versa, but to a lesser degree. ...and not only that but since the box technically has 3 hots and a neutral in it, I'd prefer they trip together, and kill the whole run.

But as Dennis said, the issue to be careful of is the voltage rating of the breaker. If the breaker says "120/240V" on the label, you cannot use it because on a 240V 3 phase 4 wire system, the voltage between B phase and ground exceeds 120V (it's 208V). So you must use a breaker that is rated for "straight" 240V. Not a big deal, just a potential "gottcha".

 

[electrofelon]

All listed multi-pole breakers have been tested for the performance for all combinations of loading. A 3 pole breaker has been tested as a 1, 2, and 3 pole devices.

UL Molded Case Circuit Breakers Marking Guide '07​

page 17​

33. 3-Pole - 1-Phase Rated - 3-pole circuit breakers are suitable for use on 3-phase systems only, unless marked to indicate use on 1-phase systems, such as, "For 1-phase connections, use two outside poles," or an equivalent statement. A 3-phase breaker used in place of a 2-pole breaker on a 3-phase system, such as a 2-pole breaker used in a branch circuit that is actually two legs of a 3-phase system, is acceptable without the 3-pole breaker being specifically marked.​

​

So is there a conflict here? I just looked at a three pole breaker and I see no "marking" indicating ok to use on single phase.

 

[petersonra]

So is there a conflict here? I just looked at a three pole breaker and I see no "marking" indicating ok to use on single phase.

the marking does not necessarily have to be on the product. It can be on the box, or as an printed insert in the box among other mechanisms.

 

[jim dungar]

So is there a conflict here? I just looked at a three pole breaker and I see no "marking" indicating ok to use on single phase.

I believe that UL item relates to using 3 pole breakers on corner- grounded systems where only 2 poles are being used to interrupt a 3-phase fault.

Think about how a 3 phase breaker may need to open a single L-G fault during normal operation. This is why UL needs to test all of the individual pole combinations of any multi-pole breaker

 

[LarryFine]

I have machines that require 20A/240V AND 20A/120V on separate plugs, and if either trips I want it all to trip, so basically 2 poles for the 240V + 1 pole for the 120V.

I'd say the safety imparted by this choice far outweighs any listing issues.

In other words, it sounds like an elegant, perfect solution for your purpose.

 

[Little Bill]

I would make sure the 120V load didn't land on the high leg.

 

[GoldDigger]

The three pole breakers I have seen are designed to connect to three separate bus tabs. In a three phase panel they will be on separate phases while if they fit in a single phase (two bus) panel they will make one connection to one bus and two to the other. What is legal must still yield to what is possible.

 

[Dennis Alwon]

The three pole breakers I have seen are designed to connect to three separate bus tabs. In a three phase panel they will be on separate phases while if they fit in a single phase (two bus) panel they will make one connection to one bus and two to the other. What is legal must still yield to what is possible.

So what is the problem if you have a 240V load and a separate 120V load?

 

[texie]

I think some here are misunderstanding the OP. He is not using this in a 3 phase panel.

 

[LarryFine]

I think some here are misunderstanding the OP. He is not using this in a 3 phase panel.

I took it to be 1ph, but would work on 3ph as long as the 1p circuit was not on a high leg as mentioned above.

 

[jim dungar]

I think some here are misunderstanding the OP. He is not using this in a 3 phase panel.

I thought it was single phase.

 

[Dennis Alwon]

It could very well be a 3 phase or single phase panel. What difference does it make as long as the high leg is dealt with if it is 3 phase.

 

[norcal]

A 3-pole breaker will have a 240V rating so where is the issue if there were to be a high leg? It appears to me the the OP just wants to use the 3-pole in a 1Ø panel though.

 

[LarryFine]

A 3-pole breaker will have a 240V rating so where is the issue if there were to be a high leg?

I believe the warning was about line-to-neutral loads; nothing new.