Switching the neutrals?

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K8MHZ

K8MHZ

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I had a peek at a custom built non UL listed piece of machinery. From the drawings, it looks like 120VAC is on one terminal of the valve solenoids, and the other terminal goes to the PLC output card.

Is that not the switching of the neutral? If so, shouldn't the neutral conductor, whether switched or not, be white or grey?
 
K8MHZ said:
I had a peek at a custom built non UL listed piece of machinery. From the drawings, it looks like 120VAC is on one terminal of the valve solenoids, and the other terminal goes to the PLC output card.

Is that not the switching of the neutral? If so, shouldn't the neutral conductor, whether switched or not, be white or grey?
Click to expand...
One side of the switch is the "grounded conductor" and should be white or grey. The other side is only grounded when the switch is closed.

Maybe the conductor color needs changed as the state of the switch changes:cool:
 
I have never seen one that switched the grounded conductor through the PLC. All of the ones I have worked on, you took the hot wire to the output card, and the switched output and grounded conductor to the solenoid coil.
 
It's fairly common to switch the common on DC circuits. Not so common on AC. Probably just the way they built it. It should work either way. Shouldn't
be a lot of work to rewire it, but would it be worth it is the question.
 
Aleman said:
It's fairly common to switch the common on DC circuits. Not so common on AC. Probably just the way they built it. It should work either way. Shouldn't
be a lot of work to rewire it, but would it be worth it is the question.
Click to expand...
And very possible someone that works with DC control systems most of the time has wired this.
 
K8MHZ said:
Is it commonplace to have such a set up?

For example:

120VAC--------(solenoid)---------O:2/8
Click to expand...

I've seen this done before, but it's not good practice. It'll work but I typically mark it up for them to correct.

If for some reason they're short wire(s), they could have wired it out this way so they have an unswitched hot out in the field. Tie the other end to ground (after your device) and presto, "problem solved." :rant: People do all kinds of goofy shit.
 
lakee911 said:
I've seen this done before, but it's not good practice. It'll work but I typically mark it up for them to correct.

If for some reason they're short wire(s), they could have wired it out this way so they have an unswitched hot out in the field. Tie the other end to ground (after your device) and presto, "problem solved." :rant: People do all kinds of goofy shit.
Click to expand...
The biggest issue with that design, is that very fact...a ground fault between the device and the PLC turns the device on.
If the control was for a motor, the switched neutral design would be a violation of 430.74.
 
Is it a netural ?

Is it a netural ?

Is it a neutral or is it a ungrounded transformer. Code says not to switch the grounded conductor.

But on the other hand I think all AC control circuits need to be grounded.
 
just the cowboy said:
Is it a neutral or is it a ungrounded transformer. Code says not to switch the grounded conductor.

But on the other hand I think all AC control circuits need to be grounded.
Click to expand...

I had thought about that. The power supply (transformer) and PLCs are not mounted to the machine. Prints were followed terminating in a j-box on the machine. It was to be connected to the real world after we left.
 
just the cowboy said:
Is it a neutral or is it a ungrounded transformer. Code says not to switch the grounded conductor.

But on the other hand I think all AC control circuits need to be grounded.
Click to expand...
If the supplying transformer is 1000 VA or less, the control circuit would not be required to be a grounded circuit. 250.21(A).
 
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