Can I run a multiwire branch circuit to a garage consisting of a #14 and a #12 ungrounded conductor and a # 12 grounded conductor?

Sometimes multi wire circuits are run in mixed wire/breaker sizes around here. One example would be a bathroom. The #14 for lighting and #12 for GFI. Myself I try to keep equipment off of lighting. I'm sure some would not like this multi wire set-up. Maybe someone could figure the math on this with extreme conditions. I doubt it would make much differance doing it this way. Never had a complaint or seen a problem. I try to tape the network together and put the breakers next to each other to avoid confusion for someone elce but thats just my thing.

Tom

Active, are you talking about NM? Where does one get such stuff?

Don't see why not... At least if neutral is not the #14.

Is this a seperate building?

Not NM. I'm allways talking pipe. Don't see much MN except code corections or some use it for UF. If I had to do a whole building with MN I would look like a Moe because not much experiance with it.

Tom

I have run a mixed size multiwire circuit before. I see no problem with it.

We remodeled a small kitchen in a office building. They had a removed a stove fed with 6/3 AC cable.

I used one side of the 6/3 to feed a 30 amp 120 volt water heater and the other side to feed 120 volt 20 amp outlets.

No worries about voltage drop.

You certainly can do this. Wait. Is this a trick question? Define garage.

[This message has been edited by Electricmanscott (edited 06-02-2005).]

No trick question. Just never did that trick before. Can't see any hazard and the reason he wanted to do it was so he can put the plugs on a 20a. circuit and the lights on a 15a. circuit. I couldn't find anything in the code that prohibited it. Thought you code aficionados knew of an article in the book that would apply. As for the definition of garage:

GARAGE
n 1: an outbuilding (or part of a building) for housing automobiles 2: a repair shop where cars and trucks are serviced and repaired [syn: service department] v : keep or store in a garage; "we don't garage our car"

Source: WordNet ® 2.0, © 2003 Princeton University




[This message has been edited by George Little (edited 06-02-2005).]

George,
Can we assume that this is an "attached" garage?

Detached Garage - I forgot to mention that.

I think you need some means of disconnecting the circuits at the detached building if there is more than one circuit

Got a disconnect in the detached garage DPST switch.

Iwire, how did you run one side of a multiwire circuit feeding a 30a load, and the other feeding a 20a load?

Do they make such a combination 30/20 2pole breaker?

Dnk....

Doesn't have to be a two pole breaker.

George you are right.

It can be a fused disconnect, but why?

They also can be single pole breakers with approved handle ties, but that would make it a 2 pole breaker for all pratical purposes.

So I ask again, Do they make 30/20 combinations 2 pole breakers?

Dnk.........

I have never seen one, there would be to little call for it.

I did not need or use handle ties, I don't remember if the 20 and 30 amp breakers where even side by side.

Dnk, there is no reason for both OCPD's to open both ungrounded conductors at the same time in this circuit.

Roger

Is that because they are not on the same yoke?

Dnk, yes. Reference 210.4(B)and 210.7(C) in the latter a multiwire branch circuit may not fit the discription. (further discussion? )

Roger

[This message has been edited by Roger (edited 06-06-2005).]

Does this "detached" structure require a seperate grounding electrode per 250-32 since this building is supplied by more than 1 branch circuit?

George,

You said that the building disconnect was a DPST switch, so let me assume for the moment that it's a snap switch (as allowed for a residential detached building disconnect). Then:

1) Wouldn't that be considered two circuits on a common yoke, leading to the requirement for a handle tie?

2) How do you handle the requirement to be able to disconnect the system neutral from the building wiring neutral? A wire nut in the switch box?

3) Since there's more than one branch circuit, the building requires its own grounding electrode, right?

(I think my own question (3) tells me that my first assumption is probably wrong, and that the DPST is actually something like a molded-case disconnect with ground and neutral bars. If so, ignore all this...)


[This message has been edited by John Crighton (edited 06-06-2005).]

Read the exception to that one. In this case a multiwire branch circuit is considered a single branch circuit.

John, I didn't say what you think I said.

As far as your 1st question, a multiwire branch circuit is one circuit, see 210.4(A) and notice the wording shall be permitted to be considered as multiple circuits.

Roger

[This message has been edited by Roger (edited 06-06-2005).]

Roger, I meant to address that to "George" -- Sorry for the confusion. I've fixed it.

I don't have my NEC at hand, but I'll have a look at 210.4. Thanks.

I'm still wondering about the breaker tie...


[This message has been edited by John Crighton (edited 06-06-2005).]

Electricmanscott,

Thanks for pointing out the multiwire circuit being a single circuit. I missed that one. I guess that's why you have achieved that superhero status!

Harold

Take a look at 225.33 Number of disconnects.

225.36 Exception from SUSE rating.

225.38 Snap switches as disconnects.

225.30 Multiwire branch circuit is one circuit.

For safety, I agree with John Crighton on the need for a handle tie with the multiwire branch circuit feeding the double pole switch.

But, the book says...

"more than one device or equipment on the same yoke" 210.4(B)

A double pole single throw switch is only one device, right?

So, no handle tie required?

shortcircuit

shortcircuit, thanks for making "the coin drop." I completely missed that a DPST switch is only one device.

That's sort of a hole in the code, isn't it? It's common for a two-pole switch to control a line-to-line load, in which case the handle tie is required anyway. In this rare case where it controls two line-to-neutral loads on a multiwire branch circuit, the lack of a handle tie would seem to be just as hazardous as if the switch were two devices.

It seems I learn something here every day. Thanks, all.

One more thing -- 210.19(A), FPN 4 recommends a 3% max voltage drop on branch circuits, and the city of Los Angeles makes it a requirement. Assuming a 16 amp max load on a 20 amp circuit, that's only 58 feet of an awg-12 pair. It's easy to exceed that when running to a detached garage, as I recently discovered.

Ok, two more things -- Can anybody explain the reason for 225.38(C)? In this case, with a snap-switch disconnect, is this met by just splicing the neutrals with a wirenut in the switch box?


[This message has been edited by John Crighton (edited 06-07-2005).]

I think you satisfy the code by simply using 2 single pole switches for the <less than six> disconnects.

BTW Florida is putting the FPN voltage drop in the energy code. I am not sure how you are going to enforce that with anything but fixed in place equipment.
I suppose you could use the article 220 load calcs and try to deduce the current in every leg of every circuit but, like flying the F117, you couldn't do it without a computer.

Not if you are doing 30 a day.

[This message has been edited by gfretwell (edited 06-07-2005).]

I believe that under the 2002 NEC a tie handle was not required for a multi-branch circuit. However in the 2005, I believe that it is going to change and a tie handle will now be required. Our state still follows the 2002 NEC for now.

That multi wire branch circuit is only one circuit. For it to be two circuits you would have to run it with separate neutrals. Since the building will be served by only one branch circuit a grounding electrode system is not required.

Since the garage is on residential property you are allowed to use snap switches as the building disconnecting means. I favor the DPST approach but that is certainly not required.
--
Tom Horne

"This alternting current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison


COPYRIGHT 2002 The National Fire Protection Association

Caper the 2005 just removed the "dwelling unit" language. The "same yoke" stayed the same. Now a commercial MW, landing on the same yoke needs a handle tie. If it splits out it doesn't.

I don't think so. If you look at the defination of a Branch circuit in Article 100 it states. The circuit conductors between the final overcurrent device protecting the circuit and the outlets.

I would tell the contractor it was ok to split the neutral on the two branch circuits but I would suggest he take a look at the requirements of 250.32.