O.T. temp wiring 208 panel single circuits

russrmartin

Member
Join Date
Aug 2002
Location
Eastman, Wisconsin
Posts
744
Hey guys, got an off topic temp wiring question for you. There's a guy here pulling 8 single phase 120 volt drops to a new box which will house 8 recepticles. Each will be on it's own circuit. The guy who told him to do this informed him to run 1 neutral with each set of 3 hots. Example, breakers 1,3,5 share a neutral, etc. My question is what is the point of this. If the neutrals carry the unbalanced load, and all 8 circuits are being pulled individually off 8 separate breakers, from the same panel, to the same location, could he not pull only 1 neutral? I guess I am confused as to why it would not be 1 neutral or 8. I haven't consulted the code book yet, because I'm lazy and thought this might be faster. If I find the answer before it shows up here, I'll answer this myself.

Russ
 
Probably a personal preference or just a means to be cheap. IFn it were me though I would run a neutral for each ckt., think code requires that too but like you too lazy to look up right now.

The reason you would never use one is the neutral is a current carrying conductor and 8 ckts, even not fully loaded, could exceed the amp rating of the neutral.

I would, if you, look up the code. Personally regardless of what code states I would make them run a neutral for each ckt.
 
Found it

I guess sometimes I ask dumb questions. I don't know what I was thinking, but yes, pulling 3 neutrals is fine as long as all 3 ungrounded conductors are opened simultaneously. I'll double check to make sure that will be the case here.
 
I suffer from a severe case of CRS

Technically I know that you can have 8 receptacles in a home on one ckt but I never apply this in industrial applications.
 
Now not so sure

Well, now that I've slowed down and reread 210-4, it appears that as long as the multiwire circuit does not feed more than one device on the same yoke, simultaneous disconnection of the ungrounded conductors is not required. This is a surprize to me, but now that I've looked it up and read it twice, I'll remember this for at least a week. :) Thanks for the input Ron.
 
I doubt very much the 8 outlets are going to be on a MWB circuit. Even if so, then it would be one grounded conductor ('neutral') for every 2 ungrounded conductors if using a center taped 240/120 secondary transformer. The OP hasn’t said that the circuit is anything other than a single phase circuit.

Show me where the phases of the ungrounded conductors are different and then it just may be a MWBC.

And, IIRC, in an industrial setting, the rule is you only have to allow 180VA per outlet receptacle when calculating load.

There is no limit on outlet receptacles in residential dwellings for a general purpose branch circuit.

For more views & comments, post the same question at MikeHolt.com
 
The original OP said that this was a 208V panel which is a standard 3 phase panel

If this is a 208V three phase panel, it is OK to have one neutral conductor per set of three receptacles provided the ungrounded conductors are all interupted by the same breaker.
 
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One of the many things that I do is teach electrical safety at my current employer (and the previous one also). This is one situation that I always teach because I have seen someone bit by this (luckily not hurt). I am attaching a simple PDF of this but the short story is this can KILL if you don't know what you are doing. It is (and was) perfectly legal by the NEC and common practice in commercial buildings (especially lighting). You don't have to open all 3 phase at the same time. I try to never let this happen on anything I am doing. I have atatched a Powerpoint of this (with sound) and a pdf of this.

Ron Doran, if you want this for your site, you have my permission (that is if you already don't cover this).
 
I thought so too originally

allscott said:
The original OP said that this was a 208V panel which is a standard 3 phase panel

If this is a 208V three phase panel, it is OK to have one neutral conductor per set of three receptacles provided the ungrounded conductors are all interupted by the same breaker.

When I first read on this, I originally thought the ungrounded conductors needed to be opened simultaneously, or, if separate, a separate ungrounded conductor was needed for each of the 8 circuits as well. After re-reading though, I agree with Bruce. This is only required if the MWB feeds 2 devices on the same yoke. In a nutshell, if the MWB feeds a duplex repecticle from which the jumper has been removed, ( leg 1 feeds top recepticle, leg 2 feeds bottom), or something of the equivalent, then all associated ungrounded conductors need to be opened simultaneously.

That will not be case, and because it is a temporary installation, we will only pull 1 neutral for each of the 3 groups of 3 legs. Were this a permanent install, we'd probably opt just to pull the extra 5 and not worry about it. Thanks to all for the input.

Russ
 
russrmartin said:
Well, now that I've slowed down and reread 210-4, it appears that as long as the multiwire circuit does not feed more than one device on the same yoke, simultaneous disconnection of the ungrounded conductors is not required. This is a surprize to me, but now that I've looked it up and read it twice, I'll remember this for at least a week. :) Thanks for the input Ron.

This one isn't how I remembered it, either.

However, the AHJ (Authourity Having Jurisdiction) had final say, and in a couple of the local towns, a 3 pole breaker would be required. However #2, they never come out to inspect commercial.
 
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