Switch Power feed - Can this legally be done?

J

Jean-Claude

Member
Location
Dallas, Tx
Occupation
IT Systems Engineer
I have two buildings side by side (a residence and a detached barn), on two separate utility meters but both fed from the same power company transformer.
I have an HVAC system in the primary residence that I wish to feed from the residence meter during day time hours, and the barn meter during evening hours (to address time of use billing). I figure the HVAC system is about 50 amps or less. I am having to keep to NEC 2020 I believe.

Can I use a transfer switch to switch the HVAC load from supply A to Supply B legally?
Would I need to placard anything indicating the HVAC has two power supplies?
 
No, not without a lot of work. (Outside Condensing unit only)
You would end up having a common path between the buildings in parallel with the neutrals. The EG from each building. IDK if it is allowed to disconnect the respective EG along with the hots in a transfer switch.
 
ptonsparky said:
No, not without a lot of work. (Outside Condensing unit only)
You would end up having a common path between the buildings in parallel with the neutrals. The EG from each building. IDK if it is allowed to disconnect the respective EG along with the hots in a transfer switch.
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HVAC shouldn't need a neutral.
 
ptonsparky said:
...but then the freon lines would still be connected. Nope, won't work.
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Would the freon lines not also switch their earth ground when the transfer took place and the condenser gets switched? That is, if the transfer switch switch the EG as well as the two 120V (240v) hot leads?
The concern then would be that the inside unit must also then be switched so that it also has the earth ground from which ever meter is powering it. Would that not address the problem you are thinking of (and prevent a potential ground loop situation)?
 
ptonsparky said:
No, not without a lot of work. (Outside Condensing unit only)
You would end up having a common path between the buildings in parallel with the neutrals. The EG from each building. IDK if it is allowed to disconnect the respective EG along with the hots in a transfer switch.
Click to expand...
Is there anyway to have both panels and both meters legally have a single, common earth ground?
 
ptonsparky said:
The neutral load of each building would be parallel via the EGs to the condensing unit unless the EG from either was disconnected at the same time as it's hots. Easy enough with a 3 pole transfer switch.
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Most HVAC has three wires.. 2 hot, and earth ground. I've never seen a 220/240 unit that needed 120v for something internally. Some may for a blower but when the unit is electric heat, it already has 240 to it, and that is used to run the fan motor.
 
Wouldnt there be the same issue now if both buildings have water service from a common metal piping system?
 
ptonsparky said:
We're all worried about the accidental situation at

sparks' when connecting gas pipe to furnace​

but not if it's knowingly done?
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Had that happen once when an AC tech was doing the spring maintenance. He had a spark across the contactor supply and earth ground which caused a pin hole in the Corrugated (CSST) gas line. The house caught fire and was a total loss. Less leaned: Never depend on the gas line for grounding. I was glad to not be the HVAC installer in that case.
 
ptonsparky said:
It's not from the unit itself but from service entrance. The EGs are bonded to the neutral at each SE. Run an EGC to the A/C unit from each panel. You now have a parallel path for the grounded or neutral conductors via the EGCs. Draw it out.
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So an option here would be to get a dual meter base, and just hook the residence up as a sub panel (or vice/versa)?
 
ptonsparky said:
You would lose the metering advantage.
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Not if one meter was supplied by one retail provider, and the other was supplied by a different provider. This is in Texas where we have the option of picking an electric provider. Different providers have different options, such as Free Nights or Free 9-5 days, etc. The basic idea is to power the AC on which ever is cheaper (or free) at any one time.
 
Jean-Claude said:
Not if one meter was supplied by one retail provider, and the other was supplied by a different provider. This is in Texas where we have the option of picking an electric provider. Different providers have different options, such as Free Nights or Free 9-5 days, etc. The basic idea is to power the AC on which ever is cheaper (or free) at any one time.
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How many separate providers are available in the neighborhood?

I can only imagine what the poles look like. :unsure:
 
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