Neutral conductor

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dave121

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I thought an intentionally grounded current carrying conductor ( neutral ), was not suppose to be run through switches. Is this correct? I can't find anything on this in the book.

Dave
 
404.2.b, got it ,
thanks

No, not if I can hook it to a switch. Using a neutral in a series circuit, through switches to hold in a 120 v. starter coil. Not my design, just questioning something I see out there.
 
dave121 said:
404.2.b, got it ,
thanks

No, not if I can hook it to a switch. Using a neutral in a series circuit, through switches to hold in a 120 v. starter coil. Not my design, just questioning something I see out there.
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You wouldn't be talking about overload relays would you?
 
Some motor-control circuits are connected line-to-line, and some line-to-neutral, depending on whether there is a neutral, obviously. A long as the coil sees its design voltage, it doesn't care.

This has been debated before, but I think anyone who argues the switching-the-neutral-is-noncompliant for control circuitry is bordering on the ridiculous. Like that's never happened before. :rolleyes:
 
LarryFine said:
This has been debated before, but I think anyone who argues the switching-the-neutral-is-noncompliant for control circuitry is bordering on the ridiculous. Like that's never happened before. :rolleyes:
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430.74 :-?
 
080509-1251 EST

dave121:

If you are describing machine control logic of some complexity, then I would argue that it is bad logic design from a troubleshooting perspective. Also it might obscure simplification of the logic circuit.

If you are looking at a conventional ladder diagram, all relays and loads will be connected to the right hand rail. All inputs will be in some form of combinatorial logic from the left rail to the output. This makes it easy to monitor the output for voltage and if it is not there then track back thru the controlling contacts to see where it is present. Put some of the logic between the right rail and the output and the procedure is more difficult.

Even if you think you simplified logic by putting contacts to the right of the output device it does not.

A great deal of older relay logic floated both rails from machine chassis and included ground fault lights.

I think a lot of newer controls are connecting the right hand rail to machine chassis. Most of these are PLC controlled so there is one switch, the PLC output, controlling the load (relay, pilot light, solenoid, etc.) and the old convention prevails of making the right rail common and the left rail hot.

.
 
wasasparky said:
430.74 :-?
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Disconnection?

Mayhaps you mean:

430.85 In Grounded Conductors. One pole of the controller shall be permitted to be placed in a permanently grounded conductor, provided the controller is designed so that the pole in the grounded conductor cannot be opened without simultaneously opening all conductors of the circuit.
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I take this to mean the grounded conductor of the controlled circuit, not that of the controlling circuit. In other words, the motor load, not the contactor coil.
 
I, in my dyslexic (dumblexic) glory, read 430.74 and looked up 430.73 which actually seems somewhat pertinent.

If that's what is being referenced, most motor starters have the overload relay about 2 inches of wire away from the coil.
 
Switches - no.

Overload relay - yes.

Personally I generally do not allow the overload realy to be on the neutral side anymore. It sometimes means a wire has to be removed, but I prefer it that way. And a fair number of specs no longer allow it.
 
A long time ago in one panel, I got a brainstorm and used the O.L. on the hot side instead of the neutral, so as not to switch the neutral.

Why, I'm not sure, wild hair up the orifice I guess... but ever since, I've been expecting someone to point out that I didn't know what I was doing. I've never done it since.

What really is the advantage to that, especially when they already come wired the other way, and the OL is a couple inches from the coil?


It's not like there's much likelihood of a fault-grounded wire holding the contactor on, when the OL would like to de-energize it.
 
I believe it is intentional that the grounded conductor is opened by the OLs.

If I recall if you do not break the grounded conductor there is a mode of failure that can hold the contactor in even if the OL opens.
 
The way I read 430.74, it is not permissible to switch the grounded conductor in any portion of the control circuit which is located remotely from the controller enclosure.

It is okay to switch the grounded conductor through the overload contact because it is not remote from the controller.

If you show me a control circuit which switches the neutral, I would bet I can show you a condition which will violate 430.74 by an accidental ground.

I don't know of any advantage to putting the OL contact in the grounded conductor versus the ungrounded conductor. I think it is just a convention that was begun way back and has become an industrial standard.
 
No, no overloads involved in this circuit. A 110 source, hot directly to the coil of a contactor, neutral of the 110 source routed through a series of switches to the contactor coil. I agree, a poor choice.

thanks all
 
An accidental ground on the hot/switched hot side of the control circuit will not cause the coil to pull in. An accidental ground on the switched neutral wiring could, under the right conditions, cause the coil to energize.
 
dave121 said:
No, no overloads involved in this circuit. A 110 source, hot directly to the coil of a contactor, neutral of the 110 source routed through a series of switches to the contactor coil. I agree, a poor choice.
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Now that I've heard this description, I concur.


crossman said:
An accidental ground on the hot/switched hot side of the control circuit will not cause the coil to pull in. An accidental ground on the switched neutral wiring could, under the right conditions, cause the coil to energize.
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This, too.
 
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