Multiwire branch circuit

[jasons]

210.4 states as follows:
branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire branch circuit shall be permitted to be considered as multiple circuits. All conductors shall originate from the same panelboard.

Definition of a multiwire branch circuit
A branch circuit that consist of 2 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.

Finally to my question

You have a raceway that has 2- ungrounded conductors each of which are from opposite phases and different OCPD, 1- grounded conductor , and 1- EGC. The 2- ungrounded conductors feed different lighting circuits. Is this considered a multiwire branch circuit?

The reason for my asking is that the definition of a branch circuit says: the circuit conductors between the final overcurrent device protecting the CIRCUIT and the outlet(s).

This definition says the circuit(cingular). My example has 2- circuits(plural).

In Mike holts Understanding the Code page 38 it says
210.4 Multiwire branch circuits
(A) General. A multiwire circuit can be considered as a single circuit or as a multiple circuit.

Multiple circuit example: The NEC requires 2 small applaincecircuits for countertop receptacles in dwelling unit kitchens(210.11(C)(1) and 210.52(B)(2)), and one single phase, 3-wire 120/240V multiwire branch circuit could be used for this purpose.

The way i am understanding this example is that the OCPD for this 3-wire circuit is a 2-pole OCPD with an approved handle tie.

If this understanding is right then my example listed above is not considered a multiwire branch circuit.

If you are not too confused please give answers

Thanks
Jason

 

[Guest]

Re: Multiwire branch circuit

It is my understanding that if the multi-wire branch circuit lands on one yoke or strap that there must be a handle-tie (Edison Circuit). 210.4(B). I interpret this to be a single circuit and that's why the handle-tie is required.

By permissive language 210.4(B) implies that if they don't land on the same yoke or strap they don't require a handle-tie. I interpret this to be multiple circuits.

Personally I like handle-ties on multi-wire branch circuits. If I feel the handle-tie will be a liability to the circuit then I reconsider and carefully weigh the decision to go with a multi-wire branch circuit. Unless there is a special request I choose to consider a multi-wire branch circuit as one circuit (with two destinations).

[ October 15, 2003, 01:53 AM: Message edited by: awwt ]

 

[iwire]

Re: Multiwire branch circuit

Originally posted by jasons:
You have a raceway that has 2- ungrounded conductors each of which are from opposite phases and different OCPD, 1- grounded conductor , and 1- EGC. The 2- ungrounded conductors feed different lighting circuits. Is this considered a multiwire branch circuit?

Yes, you are using one grounded conductor for two ungrounded conductors that have a voltage between them.

This is a multiwire branch circuit

Originally posted by jasons:
The reason for my asking is that the definition of a branch circuit says: the circuit conductors between the final overcurrent device protecting the CIRCUIT and the outlet(s).

That is correct, it is still a branch circuit, it just happens to be a multiwire one.

Originally posted by jasons:
Multiple circuit example: The NEC requires 2 small applaincecircuits for countertop receptacles in dwelling unit kitchens(210.11(C)(1) and 210.52(B)(2)), and one single phase, 3-wire 120/240V multiwire branch circuit could be used for this purpose.

The way i am understanding this example is that the OCPD for this 3-wire circuit is a 2-pole OCPD with an approved handle tie.

It could be a common trip breaker or a breaker with approved handle ties.

But unless both ungrounded conductors of this multiwire branch circuit land on the same yoke (say you break the tab off the side of a duplex receptacle to have 20 amps available in each socket) there it is no requirement to use handle ties or common trip breakers.

210.4(B) Dwelling Units. In dwelling units, a multiwire branch circuit supplying more than one device or equipment on the same yoke shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originated.

There is no other time that you are required to use a "a means to disconnect simultaneously all ungrounded conductors" for a multiwire branch circuit.

There is no rule to stop you from doing so if you would like. IMO most times I would not do this, one circuit trips and the other goes too, in my case usually the other two circuits.

Originally posted by jasons:
If this understanding is right then my example listed above is not considered a multiwire branch circuit.

If you are not too confused please give answers

Thanks
Jason

This last part I am a little confused on, I think you are saying that if you use handle ties it is not a multiwire branch circuit.

That is not correct the use of one neutral for two or more ungrounded conductors with voltage between them makes it a multiwire branch circuit, what type of breaker you use does not change this.

I hoped this was helpful and feel free to ask more questions.