is this switch broken, or is my understanding?

[jml74]

I have this motor disconnect that isn't working the way I expect it to. If I measure voltage across red and black on the input side, I get 240V. If I measure voltage across red and black on the motor side, with the switch closed, I get 0. If I measure voltage between red and ground and black and ground on the motor side, I get 120V on each. I can't think of any scenario that would show 120V on each leg, but not 240V across the two.

 

[Copymutt]

On the motor side your going to read the drop only. If it's not running one leg or both of the switch or ground would be the problem.
I'm reading between the lines that the motor is not running.

 

[PCustoms]

Is this the compressor issue I saw in another post?

Take a pic of the switch you have wired.

 

[jml74]

On the motor side your going to read the drop only. If it's not running one leg or both of the switch or ground would be the problem.
I'm reading between the lines that the motor is not running.

Correct, it's not. The thing about this switch is that it doesn't have a ground lug, so I mounted it in a metal box and grounded that (the switch does have a metal face); I ran into an electrician when I was picking up the mounting stuff and he agreed that that was a reasonable thing to do. I've kind of hit the limits of my talent here, so if you (or anyone) can help me unravel this I'd greatly appreciate it. This is the link to the product page and this is the link to the wiring directions. The schematic is silent on ground, it just has L1 and L2 on the input going to T1 and T2 on the motor. Would I be better off if I took the ground off of the box and just wirenutted the ground back like it was before I inserted the disconnect?

 

[jml74]

Is this the compressor issue I saw in another post?

Take a pic of the switch you have wired.

It is. I left that post open for now, but I did verify that I'm not getting 240V out of the disconnect, so I think that's the problem.. It's not wired in right now, I took it out to see if there was something I was missing.

 

[jml74]

I missed this in the product description before:
"40 Amp, 600V, Double-Pole, Single Phase AC Manual Motor Controller, Suitable as Motor Disconnect, Toggle, Industrial Grade, Non-Grounding, Back & Side Wiring, - Black"

What is the implication of that?

EDIT: And, by the way, that diagram I originally posted above that has ground in it came from the product page for this disconnect.

 

[BillK]

Disconnect the motor wires from the switch. Then see what you get. If one side of the switch is not closing, you will get exactly the readings you are getting. Lets say the right hand side of the switch as you have it drawn is not closing at all. The 120 v on the left side is going through the motor to the right side connection on the switch. So you will read 120 volts there but it is the same 120v you are measuring on the left side.

 

[wyliesdiesels]

Turn breaker off and measure continuity between each input/output pair.

 

[jml74]

Disconnect the motor wires from the switch. Then see what you get. If one side of the switch is not closing, you will get exactly the readings you are getting. Lets say the right hand side of the switch as you have it drawn is not closing at all. The 120 v on the left side is going through the motor to the right side connection on the switch. So you will read 120 volts there but it is the same 120v you are measuring on the left side.

OK, I see what you're saying. I'll check that tomorrow, but to the point somebody else made, I did verify continuity between each in and out with the switch closed, so it seems like the switch is actually closing. In your scenario, if I test with the motor legs disconnected I should see 120V on one and 0 on the other, right?

 

[BillK]

In your scenario, if I test with the motor legs disconnected I should see 120V on one and 0 on the other, right?

Correct if one side of the switch is not closing.

 

[jml74]

Argh. I went out and tested continuity again, and when I check on the screws between one pair of terminals I don't get anything. If I take the screws out and put the probe down in there I do get continuity, which is how I was initially testing it. So I guess I got a marginal switch.