trick question!

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Re: trick question!

I have to add the there is one breaker that's really not a tandem breaker but they serve the same purpose. The slim line GE mini breaker, I stopped using these several years ago as the 20 amp one seem prone to failure at the contact point on the buss. The one good thing is these panels also have the stabs for full size breakers which is what I used with the last ones we had in stock. Just can't put as many in it.

The other thing is the original question was
Can you feed multiwire circuits from a "Tandem" 20-20 circuit breaker?
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This would only be called a multiwire circuit if there is a voltage between both ungrounded conductors, and a voltage between each ungrounded conductor and the grounded conductor. Most tandems would not support this today.
This come from article 100 for branch circuit-Multiwire:
Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them , and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.
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So if it is not a multiwire circuit then 210.4 or 240.20(B)(1) would not apply You would think that 300.13(B) should apply but if you cant call it a multiwire circuit as per article 100 then it would be one of those tuff calls :D
 
Re: trick question!

I seem to remember Crouse Hinds made a tandem, twin or duplex (whatever you want to call it) that picked up two phases. The contact tabs did appear a little weak and small in contact area.
Does Crouse Hinds even make panelboards and C/B's anymore????
 
Re: trick question!

Originally posted by sandsnow:
Does Crouse Hinds even make panelboards and C/B's anymore????
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I'm not positive but I think they may be affiliated with Murray now.

Dave
 
Re: trick question!

"This would only be called a multiwire circuit if there is a voltage between both ungrounded conductors, and a voltage between each ungrounded conductor and the grounded conductor. "


Hey Wayne, I'm not sure I follow you on this...are you suggesting the NEC should "Define" a tandem breaker that is wired incorrectly? (2 circuits from the same phase sharing a neutral)
or
Are you suggesting it's possible to wire 2 circuits (on the same phase) sharing a neutral from a tandem breaker without a violation?

I think there are only 2 code compliant scenerios when using a tandem breaker:

1st: 2 circuits (with 2 neutrals)

2nd: A mutiwire circuit
(Only if the tandem hits both phases)


"Just adding my two cents worth."

Your 2 cents is always appreciated.

Dave
 
Re: trick question!

You've got to get up pretty early to get a trick question past this group...sort of Like Roger did when he asked how many receptacles can be on a 115 volt circuit in other than dwelling units. :D
 
Re: trick question!

Dave I was just pointing out that if the ungrounded conductors are on the same leg in a panel, it could not be called a multiwire circuit,
And certain codes would not apply. The only time I know that the NEC address's this is for outside circuits.
But keep in mind the allot of office furniture does come wire like this and has an over sized neutral and since it is UL listed it must be ok?

If you think about it every service is in fact many circuits on the same phase with a over sized neutral feeding it. :D But they do have individual neutrals after the OCPD.
 
Re: trick question!

Originally posted by hurk27:
[QB] Dave I was just pointing out that if the ungrounded conductors are on the same leg in a panel, it could not be called a multiwire circuit,
And certain codes would not apply. The only time I know that the NEC address's this is for outside circuits.
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I agree Wayne, except I'm not familiar with the "outside circuit" reference.

Well then, This is getting even "trickier" then I first thought! By wiring the tandem circuits incorrectly it is NOT a "mutiwire circuit" and so it isn't recognized by the NEC!?!?
There must be a code (I've been looking!) to prevent such an install!

So my NEW Question is: What article would be violated by wiring a tandem breaker incorrectly?
(Wired like in the original question except using a tandem breaker that does NOT hit 2 phases)
:confused:

Dave
 
Re: trick question!

I don't think you will find one. We had this discussion awhile back And if I remember right no one found one then ether.

Here is the only code reference that I know of:

225.7 Lighting Equipment Installed Outdoors.
(A) General. For the supply of lighting equipment installed outdoors, the branch circuits shall comply with Article 210 and 225.7(B) through (D).
(B) Common Neutral. The ampacity of the neutral conductor shall not be less than the maximum net computed load current between the neutral and all ungrounded conductors connected to any one phase of the circuit.
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Edit to add:
I have to add while this does describe this type of installation the NEC is in error to calling this grounded circuit conductor a neutral because it does not carry the unbalance current of two or more circuits between two legs of the panel.

[ April 05, 2005, 01:04 AM: Message edited by: hurk27 ]
 
Re: trick question!

Way too much thought into this, I think.

The neutral would not have the ampacity for the load imposed.

Such as 15 + 15 = 30 on a 14 AWG conductor, in violation of 310.15(B). Due to the limitation that a neutral cannot be protected by an OCPD, it is forced to be protected by the OCPD supplying the ungrounded conductors supplying it. But that doesn't mean the neutral's ampacity can be exceeded. ;)
 
Re: trick question!

George
225.7(B) Requires just that! Look at the bold.

The ampacity of the neutral conductor shall not be less than the maximum net computed load current between the neutral and all ungrounded conductors connected to any one phase of the circuit.
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Re: trick question!

Strange they only have this written in the Lighting Equiptment Installed
Outdoors article???

The same rule should apply to indoor circuits as well.

George, I completely understand why (In Theory) it's not permitted but I can't find an article to address it for indoor circuits!

Dave
 
Re: trick question!

Sorry George! I see exactly what youre saying now! For some reason I thought you referenced 225.7(B) also.
(I was Up too late!) :D

Thanks!

Dave
 
Re: trick question!

GE has "twin, mini,tamdem" breakers, and a panel with 16 1" slots, but the bottom 2 on each side are set up for the 1/2" breakers, which can be set up as a single pole 120V, double pole 240V, and single pole 120V. The box is rated and labeled at 20 circuits. A client I assessed last Friday, April Fools day, had been told by an electrician friend that he needed a new panel because his 16 slots were filled up. Funny, but this electrician did NOT tell him that the 10 guage wires connected to his A/C should not be connected to a 50 amp breaker!
 
Re: trick question!

Originally posted by problemsolver600:
...had been told by an electrician friend that he needed a new panel because his 16 slots were filled up....
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With friends like that, who needs Enimas!

:D
Dave
 
Re: trick question!

Originally posted by problemsolver600:
Funny, but this electrician did NOT tell him that the 10 guage wires connected to his A/C should not be connected to a 50 amp breaker!
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Where's Mr. Badger when you need him? :D
 
Re: trick question!

By problemsolver600: Funny, but this electrician did NOT tell him that the 10 guage wires connected to his A/C should not be connected to a 50 amp breaker!
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For motor loads as per 430 the breaker in the panel is only for short circuit protection and the overloads in the compressor protect the #10 wires from being over loaded. Do a search on here and you will find there are several threads on this subject.
 
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