Control Circuit Question

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msw2286

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On a starter, 480 is the line voltage for the motor. The control power is 110 volts. The push buttons are on the line side of the 110 and we have the neutral side going to the coil breaking through the overloads. Is breaking this neutral to the coil against the code and where can I find it in the code book? Thank you!
 
Breaking the grounded conductor through the overloads on a motor starter is very common.
 
While this is the standard method of wiring the overload contact into the circuit, I see nothing in the NEC that permits the switching of the grounded conductor. If the overload is factory wired as part of a listed starter, the NEC would not apply, but if you are building a control system with panel mount overload relays then the NEC would require that you wire the overload relay contact on the ungrounded side of the control circuit. Some engineers specify that the overload relay contact be on the hot side of the control power circuit, and I recall someone telling me that all GM plants have the OL relay contact on the ungrounded side. Starters are available wired this way, but they are special order.
Don
 
IMO, there is nothing wrong with the ungrounded conductor being broken in a control circuit in this manner. My logic is as follows......
a) The conductor you are breaking with the OL relay is actually the "common" conductor for the coil (in the OP's case a neutral/ungrounded wire)
b) The "actual wire that is switched for the coil is the ungrounded conductor. This conductor is routed through a holding circuit in the magnetic starter enclosure so when the "common" is broken (whether or not it is grounded or ungrounded) what you are actually doing is opening the holding circuit which, in turn opens the "switched" ungrounded conductor for the coil.

I can see arguements both ways on this issue but my opinion is stated above. I'm sure others will have other opinionsand I am interested in where this post might lead.
 
Motor control

Motor control

In your question you do not state the location of the start/stop buttons or if the neutral is located outside the starter. Your description of the configuration appears to be a normal installation with the 120v going to the stop then paralleled with the aux contact and start and finally going to one side of the coil. The neutral goes through the OL and to the other side of the coil. If for some reason the neutral is outside the starter and being used in some external control device that would allow the starter to close if the neutral were to become grounded then that would be a violation of the NEC. See 430.73.

Grant
 
Jljohnson said:
This conductor is routed through a holding circuit in the magnetic starter enclosure so when the "common" is broken (whether or not it is grounded or ungrounded) what you are actually doing is opening the holding circuit which, in turn opens the "switched" ungrounded conductor for the coil.
Click to expand...

So, you're saying that the "unless all conductors are simultaneously opened" exception applies.

Works for me!
 
The grounded conductor is most always used to open the starter coil. If you are using a 240 or 480 volt coil in a starter, then you would have to use one of the ungrounded conductors.
The grounded conductor carries the same current as the ungrounded conductor anyway, so whats the issue.
 
John Valdes said:
The grounded conductor is most always used to open the starter coil. If you are using a 240 or 480 volt coil in a starter, then you would have to use one of the ungrounded conductors.
The grounded conductor carries the same current as the ungrounded conductor anyway, so whats the issue.
Click to expand...
The issue is minimizing energized conductors, terminals, and devices when the load is de-energized. Makes work while testing an energized motor controller a bit safer to put all contacts to the L side of the coil. Why not use this safer option?
 
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