Theory Question about 240v electric furnaces

[lavacano]

Hi all,

I have a client with a 320a service feeding 2 main disconnect boxes then remotely 2 200a main breaker panels. In the heavily loaded panel I found circuits like 120v Electric Gate, Refer, Micro and an interlock for a generator.

I have installed a ATS on the generator and this heavily loaded panel. My client has been in the practice of turning off their 2 furnaces and manually switching over to Gen power.

I would like to make the whole system turnkey.

Instead of pulling all 6 240v branch feeders into the non switched panel, shouldn't I be able to pull 2 240v branch feeders (1 from each of the 2 furnaces) into the non switched panel, this should to my knowlege disable the furnace when power is on Gen only. Now I know there might be some talk about different equipment behaving differently but on 99% of the furnaces out there disconnecting one of the 240v feeders should disable the thing (and its heat pumps) correct?

 

[iwire]

It seems odd to me that you would disable the heat in an area that I assume can go below freezing.

 

[lavacano]

the generator cant handle the heat

 

[lavacano]

The furnaces are all electric with heat pumps. They probably should have been on their own 200a panel had the original installer put thought into it.

They have propane fireplace as a backup.

 

[Smart $]

...

Instead of pulling all 6 240v branch feeders into the non switched panel, shouldn't I be able to pull 2 240v branch feeders (1 from each of the 2 furnaces) into the non switched panel, this should to my knowlege disable the furnace when power is on Gen only. Now I know there might be some talk about different equipment behaving differently but on 99% of the furnaces out there disconnecting one of the 240v feeders should disable the thing (and its heat pumps) correct?

Typically, yes. Deenergize the control power source(s), you disable the system(s). Which brings up another option, which is to just leave the feeders in place and use a control relay to disable the system(s).

 

[kwired]

Typically, yes. Deenergize the control power source(s), you disable the system(s). Which brings up another option, which is to just leave the feeders in place and use a control relay to disable the system(s).

That would be easiest and least expensive way, use the control relay to interrupt the HVAC system control power and not the power circuit means light duty relay is all that is needed cutting expense even more.

 

[lavacano]

Unfortunately due to the remodel nature of this project I think it would be more feasible at this point to swap feeders around. If this is a new construction project I believe the load shedding device on the automatic transfer switch might be used in order to control how the furnace operates.

I am already having to put in one ice cube relay in order to start up the generator automatically since it doesn't have a automatic start. I am guessing that is what you would be referring to in order to disconnect the control circuits however. Correct me if I'm wrong but I think it would be to ice cube relays with a 240 V control circuit that would disconnect the control circuitry inside each of the furnaces when there's a power outage?

 

[Smart $]

Unfortunately due to the remodel nature of this project I think it would be more feasible at this point to swap feeders around. If this is a new construction project I believe the load shedding device on the automatic transfer switch might be used in order to control how the furnace operates.

I am already having to put in one ice cube relay in order to start up the generator automatically since it doesn't have a automatic start. I am guessing that is what you would be referring to in order to disconnect the control circuits however. Correct me if I'm wrong but I think it would be to ice cube relays with a 240 V control circuit that would disconnect the control circuitry inside each of the furnaces when there's a power outage?

Yes it could be 240V coil relay, or 120V coil, powered from gennie side of ATS, or perhaps use the ATS "load-shedding device". Can't see the details from here... :huh: T-stat wire from furnaces to switching location, perhaps.

Just suggesting options... not saying you have to.

PS: If you swap over feeders, make sure you do load calc for the other panel.

 

[stew]

Generac makes a Service rated Ats with 2 hvac load shedding circuits which cut the t stat circuits. you then have no Elec heat when load shedding occurs. It also has 4 more load shedding circuits to take out other high loads using the control voltage from the Ats to control contactors on those loads. It is a nice system for this application I think.