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Pool Shark
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472 Posts
Circuit Total Limiting* CTLs are designed so you won't be able to overload the bus of the panel.


Sub-panels are always an option. Interesting enough, a larger 40 circuit sub-panel could be installed as a sub-panel off the smaller 30 circuit main panel as long as the main breaker remains compliant with the smaller 30 circuit panel.

If you want in your spare time calculate your branch circuit loads with you ammeter. You may find a breaker feeding a 60 watt bulb and that is it. In which case you can free up the breaker by combining that circuit with another breaker.
 

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Pool Shark
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472 Posts
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 answer your question no as you are not figuring in the neutral current.

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

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

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

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.;)
 

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Pool Shark
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472 Posts
I find it hard to swallow that there could be more than one "Homeline" brand panel and breaker cofiguration. I cannot find any references at Square D to explain if differences exist. I just figured I was too dumb to install these things. ....
I think you're confusing the two.... because I just did. :icon_redface:
http://www.schneider-electric.us/si...&country=US&lang=EN&id=FA130326&redirect=true

Some here may not know the difference between HomeLine and QO. HomeLine is pretty much interchangeable with a lot of other breakers, whereas QO only fits QO.
 

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Pool Shark
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472 Posts
OK, prove your statement then.
Or would you rather I prove mine?

OK. Call this a MWBC:



Ball's in your court.

.
The definition is there and it simply says paraphrasing a circuit with more than one ungrounded conductor PLUS a neutral with equal voltage.

Now, I will admit I might have been a little willy nilly to just flat out say all 2-pole and 3-pole breakers are multiwire branch circuits. Motors don't require a neutral and in fact there is a whole different chapter in the NEC that deal with motor branch circuits. I might have left out that little detail.

My point was simply to illustrate that the characteristics of a multiwire branch circuit follow the principles as any other 2-pole and 3-pole circuit. They are suppose to utilize all phases.

As for your drawing...you have the double-pole switch/breaker drawn correctly.... you are feeding two ungrounded conductors...L1 goes top, L2 to the bottom. Now you show two neutrals... that kind of defeats the purpose of a multiwire branch circuit.

Ball in your court now;)
 

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Pool Shark
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472 Posts
MWBC are not required by the NEC. They are merely allowed.
Wait what..? Who said anything about NEC requiring multiwire branch circuits?

And the drawn installation is commonly used is many cases where sensitive electronics are being served. Many job specs disallow MWBCs in those instances.
So you are drawing two dedicated circuits using a double pole breaker? Which has nothing to do with multiwire branch circuits, genius.:whistling2:

So you've never hooked up a 240 air conditioner compressor, or electric water heater?
Those are not MWBCs.
You are correct. Those are motor branch circuits.

Ball may be on my side of the net, but you hit it out of bounds.
You may have an outdated rule book. I'm clearly within bounds:rolleyes:
 

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Pool Shark
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472 Posts
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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472 Posts
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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Pool Shark
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472 Posts
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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Pool Shark
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472 Posts
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.
Actually I think this would qualify....
A 240V circuit is not a MWBC.

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.
I can see where this might get confusing, at least from where I've researched. Feel free to correct me on this manner as I will admit my background is more on residential.

So here goes my thoughts...

On the commercial side of things the term single phase 208v is used to describe the connection utilizing the wild leg on a 240/120-volt 4-wire delta. To my knowledge that is it but please elaborate.
Also, there seems to be, unknowingly to me, a lot water heaters that use this very connection and the nameplate will read 208v single phase.
Moreover, on a commercial 208Y/120-volt 3-phase wye system, there is no 208v single phase, but rather 208v 3-phase.

On the residential side, the term single phase describes the 120/240 single-phase or sometimes referred to as split-phase, supplying homes.

On the down low, it is best to describe breakers in terms of there poles and not the phases they utilize. For example, 1pole, 2pole, 3pole and so on and never use the term 1phase 2phase or 3phase to describe breakers.

That's all I got to offer on that.:thumbup:

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:
I'm actually a native southern and believe me, on my worst of worst of days I make the south look like fracking geniuses. Down here they get spoon fed at the golden corral every night, idolize honey boo boo and take religion way too seriously.
:rolleyes:
 

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Pool Shark
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472 Posts
In terms of a 208/120 volt wye system, a two wire circuit using two ungrounded conductors is a single phase circuit. The phase is made between the two ungrounded conductors. Also in that same wye system a single phase circuit is made through an ungrounded conductor and a neutral. It seems like you're using two phases for your 208 volt single phase motors, water heaters, or whatever but it's not "2 phase". That is a whole other animal.
A nameplate will state the phases, as in 3phase 208v, or 1phase 240v and so on. To simply say only one phase is being used in a 208v wye system is incorrect to me.
 

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Pool Shark
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472 Posts
I agree it's tough to conceive but google "208 volt single phase" and you'll find more than enough resources to help explain how it works. I'm tapped
I did believe me. All I found on a single phase 208v single phase was when it was connected a wild leg deta 240/120
 

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Pool Shark
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472 Posts
I'm finding some serious issues with that article

208 is a special case of a wye connection. Instead of neutral being the common secondary of three transformers, each with 240 available with respect to neutral, neutral is the center tap of one transformer, and there are three hot legs, A, B, and C. A and B are 120 volts away from neutral, and they are 240 volts away from each other.
Here he is describing a 208Y/120-volt system using 240v An incorrect statement. WTF do you even read the stuff you recommend?

This configuration, three phase 240, with one phase 120/240 split, and 208, is known as quadraplex, and is a cost effective solution to providing three phase power at the same time as traditional 120/240 split phase power, to a small business.
Here here seems to be explaining how quadraplex service drops gives a business 208Y pluss 120/240V single-phase. WTF ??
 

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Pool Shark
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472 Posts
You're the one with delusions of "2 phase" all over the place
No, a nameplate will state voltage and phases...1 or 3...there is no 2 phase.
You and your buddy like to imagine I said 2 phase, but it never happen.

To get 208 you need at least two of the three phases.
I did say this ^^
This is correct because...
In a 240Y/120 wye 3-phase two of the three phases are required to get 208v. Get with it man. It's not rocket science and please, please read something before you post it.
 
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