Client has a weird demand.

[Coppersmith]

A client has mobile home park with a large clubhouse. It's one open space like a large barn. The clubhouse is being equipped with four mini-split A/C systems. Two at the east end and two at the west end. The client insists that there be a low voltage switch with pilot light at each end of the clubhouse to cut off the A/C systems when not needed (like when the building is unoccupied). The east switch will cutoff the east units and the west switch will cutoff the west units. I've drawn a diagram of a proposed system. It's only showing one unit for simplicity. The remote switch will be approximately 60 feet from the control cabinet. Does this look code compliant? Is there a better way to do this? Note that I'm interrupting only one leg of the A/C power.

 

[LarryFine]

It looks functional, but I suggest one major change: Instead of interrupting the HVAC power, interrupt the HVAC unit's red 24v thermostat wire.

You could even use its transformer, and all you need is the switch, 24v light, and 3-conductor thermostat cable. No new transformer and no relay.

This presumes the units have accessible control wiring, of course.

 

[Coppersmith]

Is this what you are suggesting? I like that a lot better.

I did a little research and found most A/C systems use 24 volt thermostat wiring like this. I'll have to verify the units they are installing have this kind of thermostat wiring. I am a bit concerned that the 24 volt power won't have enough amps to drive the pilot light. I'm not sure if 24 volt LED pilot lights are available. Guess I'll check that next.

 

[LarryFine]

Is this what you are suggesting? I like that a lot better.

That's correct. Simple, ain't it?

I am a bit concerned that the 24 volt power won't have enough amps to drive the pilot light.

I would be extremely surprised to hear it won't.

I'm not sure if 24 volt LED pilot lights are available.

Not just 24v, but 24v ac.

https://www.amazon.com/s?k=24vac+le...098296&tag=googhydr-20&ref=pd_sl_1ikcg1rh3l_e

 

[Coppersmith]

Thanks Larry!

 

[__dan]

Yes, switching of the operating control circuit may be an all class 2 wiring method. It's an easy method in this type of equipment, so the choice is less costly and can give added features, like another remote off switch. Upstream power supply for the controls has to be CL 2 rated.

In the future the main stat will be a smarter control running a cpu. Once they get network access, they're an input to a data logger, the cloud, so you may want to keep them powered steady and insert the switch contacts in series with the load control circuit. In a three wire stat, R would get steady power and you would add series contacts to the W or B.

I would (generally) verify with the manufacturer their proposed method and the best way to interrupt the operating control circuit for a remote off. Even simple units are doing a lot in auto (off), so you never know what should keep running.

 

[texie]

Is this what you are suggesting? I like that a lot better.

I did a little research and found most A/C systems use 24 volt thermostat wiring like this. I'll have to verify the units they are installing have this kind of thermostat wiring. I am a bit concerned that the 24 volt power won't have enough amps to drive the pilot light. I'm not sure if 24 volt LED pilot lights are available. Guess I'll check that next.

Larry's method would absolutely be the preferred way to do this on a standard system. However, this won't be so straight forward on a mini split system as they all use proprietary thermostat schemes. Many now have parts available to adapt them to various control schemes.

 

[drcampbell]

... Even simple units are doing a lot in auto (off), so you never know what should keep running.

Yes, even simple tasks such as keeping the thermostat's battery charged up.

 

[LarryFine]

Maybe a remote is available from the manufacturer.