Hooking up a line in a manufacturing plant that has 1 120VAC ckt for recpt. and 1 120VAC for motor controls, using foot pedals. The other electrician on the shift and myself ran 2 neutrals, the day shift guy said he would use one for both. Just wondering what most of the rest of the guys here would have done? Thanks.

I would've use one for both, but if you do you must use a pole breaker with a common trip handle. This insures that each will be on a diferent phase and that the neutral can't have power if either circuit is being serviced.

Depends how hard it was to get the other neutral there. But even if it wasnt easy I'd probably still run the separate neutral. Easier to isolate individually.

The first thing I thought of was the breaker requirement. I'm sure that it is going to be wired on 2 SP breakers, as there are no DP breakers in the panel.

Why would this multi-wire circuit need to be connected to a multi-pole common trip breaker? The NEC does not require multi-pole common trip breakers for multi-wire circuits and using one is not a good idea in my opinion. Why should you loose both circuits if one of the circuits trips?

Curt

Curt, I don't have the book with me but the NEC absolutely does require a common trip breaker for multi wire circuits. This is a double safety feature. If you don't use a common trip breaker and both circuit get put on the same phase, the nuetral may carry up to twice it's intended load(1 circuit pulls 15 amps another pulls 18 amps, then the neutral is carrying 33 amps) - Not Good!

Also both circuits must open at the same time to prevent stray voltage on the neutral when working on either circuit.

If someone doesn't beat me to it I'll cite the code in the morning when I get to the office

210.4(C)

Line to neutral loads. Multiwire branch circuits shall supply only line to neutral loads.

Exception 2.
Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch circuit overcurrent device.

This exception only requires a common trip IF you are serving a line to line load using a multiwire branch circuit.

210.4(B)
Only requires a common trip when the multiwire branch circuit is supplying more than one device on the same yoke. Even then this is only for a dwelling. Anything else doesnt require a common trip.

The above scenario isnt in a dwelling so 210.4(B) is out, and no line to line loads are served so the requirement for a common trip is out as well.

[This message has been edited by DaveB.inVa (edited 06-13-2003).]

Eagle,
With all due respect I don't think you will ever find that in the NEC.The only requirement, to my knowledge, is that a two pole breaker or handle ties be used if both circuits land on the same yoke.
Brian

2002 NEC 210.4(B) does not require a common trip breaker, this was pointed out to me on this forum in another post.

You can use a common trip breaker or you can use a approved handle ties with single pole breakers.

2002 NEC

2002 NEC Handbook commentary on this.

[This message has been edited by iwire (edited 06-13-2003).]

Just a practical reson that it may be undesirable to use a multi-pole breaker on a multi-wire circuit...
In commercial or industrial lighting, a fault on one circuit would kill all 3 or both lighting circuits. This could possibly leave a whole plant, or office wing in the dark.
Economically speaking, if you were to run a neutral (or grounded conductor ) for each circuit, you would lose all lighting bids due to excessive material costs.

Iwire & gentlemen:
Your reference to 210.4 (b) is for residential.....not comm or industrial.

IMHO, a multi-wire circuit should be on a common trip breaker, multi pole, or handle ties. This practice can prevent an incident or accident down the road.

It may not be "Code required" but it can be installed, and it may be in the job specs. If it's in the specs/design/prints, then it can be enforced by the AHJ.

John

John,
The AHJ has no business enforcing the design specs. That is between the contractor and the engineer. The inspector can only enforce the code as adopted by the local unit of government.
Don

Redsy, some good points as usual. I got the resi and industrial points of the code blurred together,again. I know, I know, it is the grounded conductor but I am so used to saying neutral, guess I need to get with the times. Thanks guys.

Hotline,


Of course it is, that was my point, there is no requirement for commercial or industrial as you know.

My customers would not like a short on one office cube circuit to take out 2 other circuits.

Now you will say do not run multiwire circuits, but I do not make the office cubes (modular office partitions) and if they are wired for common neutral that is just how it is, beyond that I prefer to use multiwire circuits.

I have never had an inspector stick his nose in job specs and will not listen to them if they do.

I have had many prints that show multiwire circuits and never have they asked for common trip.

Feel free to install common trip breakers if you like but I will not.

What accidents are you speaking of, only qualified people should be opening boxes in any environment but most certainly in commercial and industrial installations the servicing electrician should be aware of common neutral circuits.

Iwire summed it to a tee!!!
My thoughts exactly.
John

Look here:


The NEC doesn't tell you about the open neutral hazards when working on a circuit of this type, and too many have found out otherwise!

I always say that if you hear a "loud yell and then a thump" you'll probably find out that the reason was when someone was changing a ballast .... only those who are qualified persons will understand this hazard!

The rule cited above, has been in the code for many years and was designed to overcome the questions associated with common trip or handle tied circuit breakers in an offfice occupancy.

Note:

The new 2005 NEC may require "listed" instead of "approved" handle ties because in their wisdom some would allow a nail or piece of wire, and say that it is "approved"

See that definition in Article 100.

See also Article 605



[This message has been edited by Joe Tedesco (edited 06-14-2003).]

Joe
Please tell the partition manufacturers about 605.8. Have seen numerous multi wired light, switches and outlets in office partitions.
Are you saying we are not supposed to hook these up?

nesparky,
The rule does not apply to office partitions that you would be hooking up. It only applies to cord and plug connected ones.
Don

A qualified electrician will have learned one way or another about the hazards of a common grounded conductor. I always treat such conductors as live. The reason for the residential requirement is because Joe Smucketelli's brother-in-law would jump of his 12 foot ladder and break his handy neck on the TV.

[This message has been edited by Vickrey (edited 06-15-2003).]

[This message has been edited by Vickrey (edited 06-15-2003).]

Speaking of "...learning one wasy or another"

When I was first re-wiring my house (and unintentionally getting into the biz), I had switched the breakers off for the circuit in the 1900 I was replacing wire in. Went to strip the neutral for the branch circuit... strippers hit the side of the box and <<POP>> suddenly my 12ga stripper fit 10ga, and I saw purty lights!

Discovered the person who had messed around in the boxes before had piggybacked the neutrals from several circuits. (obviously)

Individual neutrals may be viewed as overkill, but I would think it makes for a safer installation.

I'm gonna give a "generally" about office partitions. "Generally", they,
1. Come with a whip of ltfmc..why, I don't know, (coffee spills)?
2. Have all the 3 (black, red, blue) phases covered, very often with a #10 neutral. Sometimes these are supplemented with a pink or purple wire for an IG circuit, this has a #12 "noodle" that "generally" has a tracer color on it. The IG grd (2nd grd) will have your normal yellow tracer.

OK

So lotsa times, I just tie all the hots together, all the noodles together, and bond both the grounds at the first chance I get.

Do you suppose that I've ever blown anybody's computer up by this practice??
It seems that the normal office cubicle draws between 1.5-4 amps each. (Add extra for Laser Printers)...S