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Pool Shark
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You've never seen a 208V single phase water heater off a 120/208V 3 Phase panel? Or baseboard heat?
That doesn't even make any sense. A 208 single phase? To get 208 you need at least two of the three phases.

That is completely false. What 480 is illustrating is 210.7.
I appreciate you pointing that out. I've learned a few things today.:thumbup:
 

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Pool Shark
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Yes, a 208V single phase circuit from a 120/208V 3 Phase service. A 2P breaker in a 3 Phase panel...not a MWBC.

I brought up a different example to help you figure this out.
Well you are mistaken. 2pole and 3pole breakers can and do exist as multiwire branch circuits. Think of a cubicle.

Your 208 "single phase" example is completely wrong and not even possible. As I said earlier, you need two of the three phases to get 208.
 

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ablyss said:
Well you are mistaken. 2pole and 3pole breakers can and do exist in single phase as well as 3 phase as multiwire branch circuits. Think of a cubicle. Your 208 "single phase" example is completely wrong and not even possible. As I said earlier, you need two of the three phases to get 208.
wtf?
 

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Well you are mistaken. 2pole and 3pole breakers can and do exist as multiwire branch circuits. Think of a cubicle.

Your 208 "single phase" example is completely wrong and not even possible. As I said earlier, you need two of the three phases to get 208.
If something specs a 30A 208V single phase circuit and you have 120/208V 3 phase in the building, how would you wire it?
 

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ablyss said:
Well you are mistaken. 2pole and 3pole breakers can and do exist as multiwire branch circuits. Think of a cubicle. Your 208 "single phase" example is completely wrong and not even possible. As I said earlier, you need two of the three phases to get 208.
Do your homework before you start with that kind of talk. A 2 wire 208 volt circuit with two ungrounded conductors is a single phase circuit no matter how you try rationalize it
 

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Yes, a 208V single phase circuit from a 120/208V 3 Phase service. A 2P breaker in a 3 Phase panel...not a MWBC.

I brought up a different example to help you figure this out.
Well you are mistaken. 2pole and 3pole breakers can and do exist as multiwire branch circuits. Think of a cubicle.

Your 208 "single phase" example is completely wrong and not even possible. As I said earlier, you need two of the three phases to get 208.
You are new here and I'm trying to help you out in a kind way. But you're not making it easy!:jester: I'm thinking you must be a transplant to the "South", because you're making us look bad!:laughing:

This whole discussion started with your statement that all 2/3-pole beakers were for MWBC. Which I (and others) told you was not correct.

No one has said that 2/3-poles can't be a MWBC, only that that is not the only (or primary) use for them.

Anytime you only use two phases you are using single phase.
Example: 240V single phase (L1-L2) load from a 120/240V 3ph system = single phase load

208V single phase (L1-L-2) resistive heater from a 208/120V system = single phase load.

So if someone asked you to hook up their 208/240V single phase water heater up, how would you wire it? Maybe a 2-pole breaker? And that would not be a MWBC.
 

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Pool Shark
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You are new here and I'm trying to help you out in a kind way. But you're not making it easy!:jester: I'm thinking you must be a transplant to the "South", because you're making us look bad!:laughing:

This whole discussion started with your statement that all 2/3-pole beakers were for MWBC. Which I (and others) told you was not correct.

No one has said that 2/3-poles can't be a MWBC, only that that is not the only (or primary) use for them.
My point behind this was, as I said earlier the definition itself simply states "a multiwire branch is any branch circuit with more than one ungrounded conductor with a neutral" and that the circuit SHOULD be on a 2/pole or 3/pole breaker. What I meant and the way I worded it came out wrong.

I won't argue with you on the clarifications of single phase. Even though it's a misnomer. I'll just say anytime you have an electrical system, you have phase(s) plural. :thumbsup:

My lack of experience in high leg deltas is pretty obvious. I'm not afraid to say it. :icon_redface: :thumbsup:
 

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ablyss said:
My point behind this was, as I said earlier the definition itself simply states "a multiwire branch is any branch circuit with more than one ungrounded conductor with a neutral" and that the circuit SHOULD be on a 2/pole or 3/pole breaker. What I meant and the way I worded it came out wrong. I won't argue with you on the clarifications of single phase. Even though it's a misnomer. I'll just say anytime you have an electrical system, you have phase(s) plural. :thumbsup: My lack of experience in high leg deltas is pretty obvious. I'm not afraid to say it. :icon_redface: :thumbsup:
You statement was that all 2 and 3 pole breakers are mwbc's and 480sparky said inaccurate and you disagreed. Motors are a huge part of being an electrician and 80% of 3 pole breakers I put in are not mwbcs they feed motors. Even if you are a residential electrician you must have installed baseboard heaters, water heaters, well pumps, condensers or air handlers that have been 240v no neutral
 

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I'm not going to let you off the hook so easily...

This whole thing started with the question....

I never understood this. If a 2-pole 30a breaker will fit on the bus, isn't that the same possible amount of current as 2 tandem 15a breakers?
To which, you answered...

To answer your question no as you are not figuring in the neutral current.

The answer is yes. Each stab (phase) would see (potentially) 30A. The neutral load is of no concern when UL/Panel manufacturers decide where tandems can go.

2 pole and 3 pole breakers are only used for multiwire branch circuits See Article 210.4 for further reading.

We've discussed how wrong this is at length already.

Article 100 Defines a multiwire branch circuit as any branch circuit that consists of two or more ungrounded conductors that have voltage between them.

You left out the part about a neutral/grounded conductor being involved as well. What you stated as the definition would, in fact, mean that all circuits containing more than one ungrounded conductor would be MWBCs.


A multiwire branch circuit is essentially a 208/240 volt system and the remaining unbalanced loads are very very little.

When talking about MWBC's, many times the loads served are general purpose lighting/receptacles. In that case, you have no idea what the unbalanced load would be. You do know it cannot be over the rating of the circuit, but to say they are "very very little" is not always accurate.

In your example two tandem breakers may or may not be on the same phase. This not only puts all the load on one phase and directly the neutral, it also creates a risk for injury because the circuit is still open if only one tandem breaker is turned off.

CTLs are mainly a residential restriction. Non-CTLs have no limit to the amount of breakers.;)
Which some of it is misleading, and some of it is wrong. My explanation is in blue.

Then you chose to argue about how wrong we were. You even said a 208V single phase circuit was not possible. The term "single phase" may be misleading to a DIYer, but for someone claiming to be an electrician, they should know exactly what is being described when they see what voltage is involved.

It's OK to not know anything or to be corrected, that is how we all learn.
 

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btw there was a company called CLASSIFIED that made breakers that would fit a QO panel. if memory serves me right , SQ D filed a lawsuit against them for patent infringement. plus i belive they made brekers for other panels also, just don't rember who.:whistling2:
 
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