Tandem Breakers In a Three Phase Panel

[Roupus]

I see a lot of topics on tandem breakers in single phase panels but none on three phase. I understand that for three phase you need a balanced load so you can share a neutral with the three phases in the panel. So for example installing a tandem breaker I would throw the breaker say on Phase A and then take another hot from Phase A and put it on the tandem freeing up a space.

 

[fmtjfw]

If you have single phase loads that need the line-to-line voltage, 2-pole breakers are the thing to use. If you have several of these loads that are the same or nearly so, using 2-pole breakers side-to-side will help balance the load on the 3-phase.

For instance if you have a group of 208V window air conditioners on 208/120 service, you can hook them up on:

(position-phase position-phase)
1-A 3-B = A/C 1
5-C 7-A = A/C 2
9-B 11-C = A/C 3

This puts two units each on phases A, B and C.

Using 3-pole breakers requires 50% more space and for you to manually rotate the empty pole to accomplish the same thing.

[unused]
1-A 3-B [5-C] = A/C 1
7-A [9-B] 11-C = A/C 2
[13-A] 15-B 17-C = A/C 3

This same scheme would apply if the loads involved the neutral (clothes dryers for example).

 

[infinity]

I see a lot of topics on tandem breakers in single phase panels but none on three phase. I understand that for three phase you need a balanced load so you can share a neutral with the three phases in the panel. So for example installing a tandem breaker I would throw the breaker say on Phase A and then take another hot from Phase A and put it on the tandem freeing up a space.


View attachment 9208

If these are MWBC's the you cannot do what's depicted in the graphic. The CB moved up to give you the "free space" is required to be handle tied to the other CB(s) sharing the neutral in the MWBC.

 

[templdl]

Of it has already been confirmed that the panel is listed for tandem breakers, correct?

 

[growler]

I see a lot of topics on tandem breakers in single phase panels but none on three phase. I understand that for three phase you need a balanced load so you can share a neutral with the three phases in the panel. So for example installing a tandem breaker I would throw the breaker say on Phase A and then take another hot from Phase A and put it on the tandem freeing up a space.


View attachment 9208

There is really not that much use for a tandem breaker in a three phase panel as these are full sized panels and will already have spaces for the maximum number of circuit allowed. If it's a 42 position panel it will already have 42 regular sized spaces.

If there was a bad section ( burned) where the breaker snaps in and you could move the circuit to a new location you would have to be carefull that it has a seperate neutral pulled for both circuits on that phase.

What I'm getting at is that if you use that "new free space" then you will have overfilled the panel.

 

[fmtjfw]

Sorry, I misread tandem as 2-pole

Sorry, I misread tandem as 2-pole

If you have single phase loads that need the line-to-line voltage, 2-pole breakers are the thing to use. If you have several of these loads that are the same or nearly so, using 2-pole breakers side-to-side will help balance the load on the 3-phase.

For instance if you have a group of 208V window air conditioners on 208/120 service, you can hook them up on:

(position-phase position-phase)
1-A 3-B = A/C 1
5-C 7-A = A/C 2
9-B 11-C = A/C 3

This puts two units each on phases A, B and C.

Using 3-pole breakers requires 50% more space and for you to manually rotate the empty pole to accomplish the same thing.

[unused]
1-A 3-B [5-C] = A/C 1
7-A [9-B] 11-C = A/C 2
[13-A] 15-B 17-C = A/C 3

This same scheme would apply if the loads involved the neutral (clothes dryers for example).

:dunce:

 

[templdl]

There is really not that much use for a tandem breaker in a three phase panel as these are full sized panels and will already have spaces for the maximum number of circuit allowed. If it's a 42 position panel it will already have 42 regular sized spaces.

If there was a bad section ( burned) where the breaker snaps in and you could move the circuit to a new location you would have to be carefull that it has a seperate neutral pulled for both circuits on that phase.

What I'm getting at is that if you use that "new free space" then you will have overfilled the panel.

To my point, 42 spaces, 42 poles. Should tandem be allowed the number of poles would be more. As such where is this series of posts going other than being theoretical.

 

[Roupus]

If these are MWBC's the you cannot do what's depicted in the graphic. The CB moved up to give you the "free space" is required to be handle tied to the other CB(s) sharing the neutral in the MWBC.

These are MWBC, Phase A,B,C or Circuit position 1,3,5 share a neutral, same as 2,4,6 and so forth. So in order to properly install a tandem breaker in a three phase panel where there are MWBC what would have to be done?

 

[GoldDigger]

These are MWBC, Phase A,B,C or Circuit position 1,3,5 share a neutral, same as 2,4,6 and so forth. So in order to properly install a tandem breaker in a three phase panel where there are MWBC what would have to be done?

Both loads of the tandem breaker can not be part of one MWBC. Run a separate neutral for one of them. The other handle of the tandem breaker would have to be tied to the breakers below it, which could be a problem.
Or both halves of the tandem breaker would be single phase circuits with separate neutrals and the MWBC would have to use the next three positions down (3,5,7) instead.
Unless you are using a GFCI or AFCI breaker, the neutrals are associated with the wires, not with either the breakers or the breaker positions.

 

[Roupus]

Both loads of the tandem breaker can not be part of one MWBC. Run a separate neutral for one of them. The other handle of the tandem breaker would have to be tied to the breakers below it, which could be a problem.
Or both halves of the tandem breaker would be single phase circuits with separate neutrals and the MWBC would have to use the next three positions down (3,5,7) instead.
Unless you are using a GFCI or AFCI breaker, the neutrals are associated with the wires, not with either the breakers or the breaker positions.

So the only way to install a tandem in a three phase panel where all the circuits are sharing neutrals such as 1,3,5 share a neutral, 7,9,11 share and so forth, is to run new neutrals for some of these circuits.

 

[ritelec]

If these are MWBC's the you cannot do what's depicted in the graphic. The CB moved up to give you the "free space" is required to be handle tied to the other CB(s) sharing the neutral in the MWBC.

I have to do some reading. Thought that was when the
Circs where installed on one yoke.

It probably changed to any multi wire.
Argh

 

[GoldDigger]

So the only way to install a tandem in a three phase panel where all the circuits are sharing neutrals such as 1,3,5 share a neutral, 7,9,11 share and so forth, is to run new neutrals for some of these circuits.

Yes.
And even then under 2011 code you would have to fabricate some handle ties that probably do not exist ready-made. Or unnecessarily tie both handles of your tandem to the two breakers below them.

 

[infinity]

I have to do some reading. Thought that was when the
Circs where installed on one yoke.

It probably changed to any multi wire.
Argh

Look at 210.4(B).

 

[templdl]

I have to do some reading. Thought that was when the
Circs where installed on one yoke.

It probably changed to any multi wire.
Argh

Is the Panel listed for a tandem breaker or are you trying to justify a way to use them?

 

[Roupus]

Is the Panel listed for a tandem breaker or are you trying to justify a way to use them?

It is just a question, lets say there are spaces in the panel that tandem breakers are allowed to be used in. I know with single phase panels when you have a MWBC lets say a 14/3 you would have to split up the two hot legs (you could not have both the hots on the tandem). Now in a three phase panel how would you organize say a MWBC that comes in on a 14/4.

 

[templdl]

It is just a question, lets say there are spaces in the panel that tandem breakers are allowed to be used in. I know with single phase panels when you have a MWBC lets say a 14/3 you would have to split up the two hot legs (you could not have both the hots on the tandem). Now in a three phase panel how would you organize say a MWBC that comes in on a 14/4.

Just a theoretical question then not that you are intending to do this.

 

[Roupus]

Just a theoretical question then not that you are intending to do this.

It is on a certain job where the panel is all lighting so three circuits share a neutral and this is the case for the entire panel. Now I need to free up a space in this panel.

 

[mjf]

It is on a certain job where the panel is all lighting so three circuits share a neutral and this is the case for the entire panel. Now I need to free up a space in this panel.

"sub-panel"

 

[GoldDigger]

It is on a certain job where the panel is all lighting so three circuits share a neutral and this is the case for the entire panel. Now I need to free up a space in this panel.

Based on the design and rating of the panel, as well as the way the wiring goes to existing loads, you may not be able to do this in a way that complies with NEC and also the manufacturer/UL limitations on use of the panel.
Anything you do could either exceed the number of circuits allowed for the panel or require changes to the setup of all of the breakers in the panel. If it is grandfathered in to not require handle ties, any changes you make to the breaker configuration may give up that grandfathering.
To give a more complete opinion we would need to know the exact model information on the panel and the code cycle you are operating under.

 

[templdl]

Finally.'why wasn't this stayed in the OP. It would have saved a lot of time. I have addressed application question for 18 years for two of the largest electrical equipment manufacturers and have grown accustomed to those who ask questions in such a way in order to get an answer that they want to hear. I believe that we have finally reached the point where trying to add a tandem breaker to the panel as described'is not allowed and is in violation of the NEC.
Now what, as mjf suggests sub panel?
It's not a matter of a code cycle but how the panel is listed by UL which I highly doubt if it is.