industrial electrical question

[ronpurdy]

Hi everyone,

At work, we had some electrical work done and I wanted to know if it is OK to use a smaller neutral conductor than the hot conductor. We have a 30 amp 120 volt circuit that is wired with a 10 awg hot and a 12 awg neutral. It is a dedicated circuit for a packaging line equipment with a 21 amp max draw. Is that acceptable? They did have 5 duplex 20 amp receptacles pigtailed on to this circuit but we had them change it.

Thanks for any help!

Ron

 

[rlitman]

Not like that is isn't.
In three phase use, it is often common to use a BIGGER neutral than phase conductor. Never smaller.

That being said, I can think of possible (albeit not common) scenarios where it would be acceptable to put a 30A breaker on a 12 gauge wire. This can ONLY occur with a circuit for dedicated equipment though, and not in all cases.

 

[sam.coll]

does the machine have a 3 phase motor? Its actually common for a 3 phase circuit to have a SMALLER neutral conductor, this is because on a balanced 3 phase load there should be close to 0A of return current in the neutral.

 

[laser3kw]

check out your post in the "electrical" forum. Somebody answered it there.

(3 phase should not have a "neutral" - at all. "PE" or earth ground - yes)

 

[rlitman]

(3 phase should not have a "neutral" - at all. "PE" or earth ground - yes)

Three phase motors use delta. No neutral wire at all, and NEVER a smaller neutral wire than the phase wire, if it exists.

Three phase wye circuits most definitely have a neutral. And because of the nature of harmonics on a three phase system, triplen harmonics (harmonic numbers divisible by three) travel on the neutral wire in an otherwise balanced system. In wye panels with large well balanced loads of computers (such as in data centers, and in office cubicle spaces), the harmonics generated by their power supplies can cause harmonic currents on the neutral wire that can exceed the breaker rating, when you would expect the neutral to have zero current, due to the balanced load. Neutral wires are often spec'd to have 150% of the ampacity of the phase wires because of this.

Here's another explanation:
http://www2.schneider-electric.com/...ang=en&locale=en_US&id=FA212226&redirect=true

Now you learned something. But this has nothing to do with the OP's question.

 

[sam.coll]

Your power systems and regs must be different in the states then they are over here then.

 

[laser3kw]

Now you learned something. But this has nothing to do with the OP's question

Yes, I did!
Never say never!
I am more electronic than industrial. That's one benefit of this site, you can get an eduction if you want to. I have learned alot on the electrical forum as well as the others. Really has helped me with my new garage paint and finish, electrical (meeting code) and tool selection.

 

[Tim37]

Hi everyone,

At work, we had some electrical work done and I wanted to know if it is OK to use a smaller neutral conductor than the hot conductor. We have a 30 amp 120 volt circuit that is wired with a 10 awg hot and a 12 awg neutral. It is a dedicated circuit for a packaging line equipment with a 21 amp max draw. Is that acceptable? They did have 5 duplex 20 amp receptacles pigtailed on to this circuit but we had them change it.

Thanks for any help!

Ron

I'm gonna assume that since you said 120 that is single phase and in that case the neutral needs to be the same size.

In a three phase all three hots need to be the same size but I have seen the ground be a lot smaller