Lighting Contactor

[spinnakerdr]

I have installed a lighting contactor with a 24 Volt coil and I can control it perfectly when the length of the 24 volt wire is less than 20 feet. However when we tried to add a 3 way switch to control the contactor 225 feet away, the contactor will not engage. It buzzes like its trying and the voltage drop on the 24 volt side goes to 14 volts (current reads 2.2A). I have checked voltage drop for the wire used for the 3 way wire loop length (12 awg wire @ 550 feet loop length) and it should only be 0.56 volts at 0.5 amps. The contactor only draws 0.5 amps when it is on and holding. Maybe there is an inrush, but my meter cannot measure it. The transformer powering the 24 volt source is rated at 200VA. Thanks for the help.

 

[infinity]

I would use a higher voltage for the switch loop and then step it down on the contactor end with the 200va transformer. Won't help you much if the switching isn't employing a chapter 3 wiring method.

Welcome to the Forum.

 

[LarryFine]

My solution would be to switch a small relay with the 3-ways, for lower coil current, and use its contacts to switch the contactor.

 

[ericsherman37]

Had a similar issue a few years ago at an RV park building we wired. The building was a combination dwelling unit (for the park manager or whoever) and an office. The highway sign for the park had a neon "NO" light (in front of "VACANCY" of course) that they wanted to be able to flip on and off from a light switch in the office. As the wire ran, the box containing the 24 V contactor and transformer was about 120' away from the switch (240' total wire circuit length). Ran on some regular ol' doorbell wire. Tried the whole thing out, and the contactor coil would hum but not engage unless you manually pushed it in. So short of pulling an entirely new wire and running a 120 V switch loop out and back, we just upsized the transformer a little bit and that gave it enough "oomph" to push enough voltage out and back to make the contactor go.

And from that, I learned how to better design and plan long runs of low voltage control wiring to avoid that sort of issue in the future

 

[infinity]

My solution would be to switch a small relay with the 3-ways, for lower coil current, and use its contacts to switch the contactor.

I like Larry's idea.

 

[dbuckley]

Larry's idea is good.

I suspect that the contactor needs more current to pull in than it needs to hold, and the additional current is causing additional voltage drop, so the contactor can't pull in.

A smaller relay will have a much lower coil resistance.

 

[LarryFine]

A smaller relay will have a much lower coil resistance.

Higher, actually, but who's counting?

 

[dbuckley]

Good lord; did I really write that?

Of course, I meant a higher resistance, resulting in a lower current

Doh.

 

[iwire]

Good lord; did I really write that?

1600+ helpful and intelligent posts .......... I think we can forgive a single error.

 

[Barndog]

I also agree with putting a smaller relay. We had a do that before where i work. after we did that it worked fine