I was currently working in a store where I had to install two switches to control 6 existing lighting contactors One switch controlled five the other switch controlled one. Where my contactors where mounted had a existing nipple to the panel. I sent my neutral directly from the panel to the contactor. And I installed a 12-2 mc to switches around 50ft from the box. When everything was wired and I turned the switches on with the switch on I was getting 120 volts to the coil. However with the switch off I was getting 24 volts which was pulling the contactors in. After realizing the problem I pulled neutrals to my switch box then to my contactors. Even with the wires disconnected from the switch I was still getting 24 volts. After pulling my neutrals to the switch box and then to the contactor the problem was resolved. Can anyone explain the theory of this to me I would greatly appericate it. Thanks
Dead end switch
- Thread starter joe2511
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- Location
- Massachusetts
I am having a real hard time understanding how 24 volts could pull in a 120 volt contactor.
What kind of contactors were they?
What kind of contactors were they?
J.P.
Senior Member
- Location
- United States
Illuminated switches? I have seen them make a cfl strobe when the switch is off.
I can't imagine they would be able to activate a 120v contactor.
I can't see how pulling the neutrals to the switch box would have changed anything, or be necessary.
The contactors should be fine with one side hooked directly to the neutral bar. Your just breaking the hot with the switches.
Are you running a separate circuit for your control circuit? You should.
Is there any emergency lighting on the circuit? If your sharing power for your switches with the contactor you may have a emergency light backfeeding. But you would have to had to have wired something wrong to get that result.
Your power to the lights should go from the breaker to the contactor and straight to the lights.
Your switch power should go from the breaker to the switch then to one side of the coil. There really isn't a possibility of any actual voltage with the switch off as far as I can see.
I can't imagine they would be able to activate a 120v contactor.
I can't see how pulling the neutrals to the switch box would have changed anything, or be necessary.
The contactors should be fine with one side hooked directly to the neutral bar. Your just breaking the hot with the switches.
Are you running a separate circuit for your control circuit? You should.
Is there any emergency lighting on the circuit? If your sharing power for your switches with the contactor you may have a emergency light backfeeding. But you would have to had to have wired something wrong to get that result.
Your power to the lights should go from the breaker to the contactor and straight to the lights.
Your switch power should go from the breaker to the switch then to one side of the coil. There really isn't a possibility of any actual voltage with the switch off as far as I can see.
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This is exactly what I expected no problem with wiring it the way that I did. With a 100 percent certainty it was the neutrals. Once I pulled the neutrals to the switch box it corrected the problem. The line and load circuits where completely separate from the contactors. And it was just not one contactor it was pulling in it was 7 I believe on both switch legs
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
140808-2145 EDT
joe2511:
Are the contactors solid-state or controlled by a small solid-state relay? If so, then capacitive coupling between the wires in the two wire switch circuit could possibly have enough capacitive coupling to provide 25 V from a 120 V source.
An AB #2 electromechanical starter with a 120 V coil does not even buzz with a 1 ufd capacitor from 120 V. This is an impedance of about 2600 ohms. With this combination the coil voltage is only 3 V. It would take about 10,000 ft of cable to produce 1 ufd.
You need to more accurately define your circuit, and where and how you made the voltage measurements..
.
joe2511:
Are the contactors solid-state or controlled by a small solid-state relay? If so, then capacitive coupling between the wires in the two wire switch circuit could possibly have enough capacitive coupling to provide 25 V from a 120 V source.
An AB #2 electromechanical starter with a 120 V coil does not even buzz with a 1 ufd capacitor from 120 V. This is an impedance of about 2600 ohms. With this combination the coil voltage is only 3 V. It would take about 10,000 ft of cable to produce 1 ufd.
You need to more accurately define your circuit, and where and how you made the voltage measurements..
.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Not at all likely. (As your calculations show.) A phantom voltage on a high impedance meter, sure. But enough to drive a relay, no.
I have not drawn out all of the possibilities, but I can envision a situation in which a miswired neutral connection on the 24V supply (transformer? DC supply?) could produce a feed through of 24V through a load to a wire that is not supposed to be connected directly to the supply.
Similar in some ways to a lost neutral on an MWBC, but less damaging.
J.P.
Senior Member
- Location
- United States
What you are describing. A constant 24v that is capable of pulling in a 120v contactor just doesn't seem possible.
I often wire shops like this and either use momentary switch at each door and latching relays or 3 & 4 way switches and definite purpose contactors.
I've never encountered anything like what you are describing. I can see a phantom volt reading, but it wouldn't activate a contactor.
What kind of contactor where you using?
What controlled the contactors before you added switches?
What voltage is your control circuit?
What voltage is your lighting circuit?
I often wire shops like this and either use momentary switch at each door and latching relays or 3 & 4 way switches and definite purpose contactors.
I've never encountered anything like what you are describing. I can see a phantom volt reading, but it wouldn't activate a contactor.
What kind of contactor where you using?
What controlled the contactors before you added switches?
What voltage is your control circuit?
What voltage is your lighting circuit?
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