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anbm

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Can a single-phase electrical panel feeds a 3-pole branch breaker?
 
You're probably going to have to be more specific. As far as I know, it is possible to physically put a 3-pole breaker in a single pole panel.

Having said that, it probably violates the NEC, it would not be a 3 phase circuit, and it is definitely not a good idea. :)

If that didn't cover the reason you're asking then give a bit more detail. :cool:
 
drbond24 said:
You're probably going to have to be more specific. As far as I know, it is possible to physically put a 3-pole breaker in a single pole panel.

Having said that, it probably violates the NEC, it would not be a 3 phase circuit, and it is definitely not a good idea. :)

If that didn't cover the reason you're asking then give a bit more detail. :cool:
Click to expand...

I am just curious...that's all, what section of NEC does not allow it?
 
anbm said:
I am just curious...that's all, what section of NEC does not allow it?
Click to expand...

Anbm,

It would amount to 3 Single-Phase circuits working together on a common trip.

Of course, Phases are "A","B","A", which on the surface seems unusual.

I could imagine a 240 motor and an auxiliary 120 device working together on a common CB.

:smile:
 
The only issue would be the panel listing. Obviously if you could use a 3 pole breaker you would have to upsize your neutral if you were running a mwbc.

I really don't think the listing would allow this install.
 
As stated by Dennis, all panelboards will have a label which indicates all breaker types and models suitable for use in the panelboard. Just because it may work, and may even be of the same brand, it doesn't necessarily mean it is permitted or will be approved.
 
anbm said:
I am just curious...that's all, what section of NEC does not allow it?
Click to expand...
Not sure it is specifically covered, because it would be a stupid thing to do. If you have a 1 phase panel, the bus bars distribute power from the two lines of the same voltage; 240V right? So on one side of the panel, they go
L1,
L2,
L1,
L2,
L1,
L2,
etc.

If you can plug in a 3 pole breaker, let's say starting from the top, the two outer poles would both end up as L1 and the center would be L2. What would you feed off of that? Say you fed a 240V 1 phase load like a 30A dryer from poles 1 and 2 and another 120V load off of the bottom pole, let's say a 120V 30A heater. If the heater overloaded, it would trip off the dryer, and vice versa. In addition, if someone inadvertently connected a 240V load to the two outer poles, they would only get 2 hot legs of the same 120V circuit and no neutral. That sets up a number of potentially dangerous scenarios.
 
I could envision a situation where a single phase (2 pole 240v) and a 120v circuit would want to be under the same handle for safety reasons. Like if they both fed one piece of equipment. That being said I also can't envision myself ever wiring something that way.


My 2?
Doug S.
 
A delta breaker is not the same as a three pole breaker.
Click to expand...

While this statement is true, Hillbilly1 had the right idea. NEC section 408.36(C) Delta Breakers states that "A 3-phase overcurrent device shall NOT be connected to the bus of any panelboard that has less than 3-phase buses."

So the answer is no, you cannot connect a 3 pole circuit breaker to a single phase panel because it would violate the NEC.
 
david luchini said:
While this statement is true, Hillbilly1 had the right idea. NEC section 408.36(C) Delta Breakers states that "A 3-phase overcurrent device shall NOT be connected to the bus of any panelboard that has less than 3-phase buses."

So the answer is no, you cannot connect a 3 pole circuit breaker to a single phase panel because it would violate the NEC.
Click to expand...

Not Correct - A 3-pole breaker is not a "delta breaker" as referenced.

A 3-pole breaker would be within it's ratings - as it would be 120/240V rated.

The listing of the panel should be checked. If the listing only includes references to 1-pole and 2-pole cb's then I would guess that 3-poles would not be allowed. If it only references a circuit breaker type (ie QO) with no reference to the number of poles, then I belive 3-pole would be legal.
 
wasasparky said:
Not Correct - A 3-pole breaker is not a "delta breaker" as referenced.

A 3-pole breaker would be within it's ratings - as it would be 120/240V rated.

The listing of the panel should be checked. If the listing only includes references to 1-pole and 2-pole cb's then I would guess that 3-poles would not be allowed. If it only references a circuit breaker type (ie QO) with no reference to the number of poles, then I belive 3-pole would be legal.
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Wasasparky, I'm afraid it is you who are incorrect. NEC 408.36(C) states "A 3-phase disconnect or overcurrent device shall not be connected to the bus of any panelboard that has less than 3-phase buses. Delta breakers shall not be installed in panelboards."

This section NEC 408.36(C) prohibits BOTH the installation of Delta breakers in panelboards AND the installation of 3-phase breakers in panelboards that have less than 3-phase buses.
 
david luchini said:
Wasasparky, I'm afraid it is you who are incorrect. NEC 408.36(C) states "A 3-phase disconnect or overcurrent device shall not be connected to the bus of any panelboard that has less than 3-phase buses. Delta breakers shall not be installed in panelboards."

This section NEC 408.36(C) prohibits BOTH the installation of Delta breakers in panelboards AND the installation of 3-phase breakers in panelboards that have less than 3-phase buses.
Click to expand...

I see your point, but 408.36(C) is titled "Delta Breakers". IMO this section is to apply specifically to delta breakers as titled. Poor wording leads us away from the original intent. If it was a universal rule, then there would be no need to title it "Delta Breakers" - it would simply need to be titled "Three-Phase Breakers"...

Anyone have a single-phase panel handy to see if the number of poles are listed? Otherwise I'll check my panel when I get home...
 
wasasparky said:
I see your point, but 408.36(C) is titled "Delta Breakers". IMO this section is to apply specifically to delta breakers as titled. Poor wording leads us away from the original intent. If it was a universal rule, then there would be no need to title it "Delta Breakers" - it would simply need to be titled "Three-Phase Breakers"...

Anyone have a single-phase panel handy to see if the number of poles are listed? Otherwise I'll check my panel when I get home...
Click to expand...

I agree with you that the section is poorly titled as "Delta Breakers." But if was meant to apply only to "delta breakers" then the section text would simply read "delta breakers shall not be installed in panelboards." There would be no need for the sentence about "3-phase disconnects or overcurrent devices."

I don't think anyone could argue that a "3-phase disconnect" and a "delta breaker" are the same thing, so obviously the two sentences are discussing different devices.
 
david luchini said:
I don't think anyone could argue that a "3-phase disconnect" and a "delta breaker" are the same thing, so obviously the two sentences are discussing different devices.
Click to expand...
I can. A Delta breaker is a 3-pole breaker that only receives power from two panel buses. The third pole get's its power from an external input, not unlike a GFCI's neutral terminal, which has no panel main terminal.

I have pointed out in the past that a high-leg Delta service is, with the exception of the high leg, identical to a 120/240v 1ph service, and that early high-leg services were actually modifications to 1ph services.

The Delta breaker allowed a 1ph panel to supply a 3ph load by having the high leg brought into the panel for the sole purpose of feeding the Delta breaker's third conductor, and the breaker to operate properly.
 
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