208v

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Jrh62972

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I have to run a single phase 208 v circuit for a mini split hvac . This will be 20 amp , 2 hits and a ground to the unit . I have a 120/208 3p panel that I want to put a 2 pole 20 amp breaker to feed the disconnect . Am I doing the right thing here and will I have the voltage I need at the disconnect
 
What does the name plate on the HVAC say for maximum OCP. That's what I use to size breakers.

BTW, you will also need a neutral for your convenience outlet required by the NEC. Unless there is already one within 25'.
 
Jrh62972 said:
I have to run a single phase 208 v circuit for a mini split hvac . This will be 20 amp , 2 hits and a ground to the unit . I have a 120/208 3p panel that I want to put a 2 pole 20 amp breaker to feed the disconnect . Am I doing the right thing here and will I have the voltage I need at the disconnect
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Sounds correct. A 120/208V supply has 208V between any two (AB, BC, and AC) hots. It also has 208V across 3 poles for 3ph loads. All three phases are 120V to neutral as well, so if you need the aforementioned receptacle required by 210.63 (or 210.64, cant remember exactly atm), you can use either hot and a neutral to supply that as well.

The only time you'd see a third voltage in a 3ph panel is with a high leg delta. Any phase-phase would be 240V, and 3ph is 240V. A-->N and C-->N are 120V, but phase B-->N is 208V. Most of these panels will have every 3rd breaker skipped.

eta: the unit may need a neutral as well; check the installation instructions. and welcome to the forum.
 
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JFletcher said:
Sounds correct. A 120/208V supply has 208V between any two (AB, BC, and AC) hots. It also has 208V across 3 poles for 3ph loads. All three phases are 120V to neutral as well, so if you need the aforementioned receptacle required by 210.63 (or 210.64, cant remember exactly atm), you can use either hot and a neutral to supply that as well.

The only time you'd see a third voltage in a 3ph panel is with a high leg delta. Any phase-phase would be 240V, and 3ph is 240V. A-->N and C-->N are 120V, but phase B-->N is 208V. Most of these panels will have every 3rd breaker skipped.

eta: the unit may need a neutral as well; check the installation instructions. and welcome to the forum.
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Thank You! The unit only requires two hot wires and a ground and then 3 wires back from outdoor unit to indoor unit. The third wire is a communicator through voltage from what I understand . The unit name plate says a max of 20amps and minimum of 15 .

So so your saying I can pull a neutral and take one leg of the hots used to feed unit and power a receptacle near unit?
 
hbiss said:
Noooooo. Separate 20A circuit.

-Hal
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I've always pulled separate circuits also. But is pulling off the line side of the disconnect prohibited by the NEC? It seems like it could cause problems and that's why I've never done it. But......

210.63 ends with "The receptacle outlet shall not be connected to the load side of the equipment disconnecting means."

Does this grant us permission to connect the outlet to the line side?
 
Depending on the amperage of the unit you may be able to feed the receptacle of one leg if a neutral is present.

210.23(A)(2) Utilization Equipment Fastened in Place. The total
rating of utilization equipment fastened in place, other than
luminaires, shall not exceed 50 percent of the branchcircuit
ampere rating where lighting units, cord-and-plugconnected
utilization equipment not fastened in place, or
both, are also supplied.
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I've always pulled separate circuits also. But is pulling off the line side of the disconnect prohibited by the NEC? It seems like it could cause problems...
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You size the breaker for the nameplate max on the AC unit. What do you think is going to happen when the AC tech plugs his vacuum pump into a receptacle supplied by the same breaker? Does he need to be careful to not switch the pump on while the AC is running?

-Hal
 
hbiss said:
You size the breaker for the nameplate max on the AC unit. What do you think is going to happen when the AC tech plugs his vacuum pump into a receptacle supplied by the same breaker? Does he need to be careful to not switch the pump on while the AC is running?

-Hal
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What Dennis said may or may not allow the receptacle on the circuit at all, you also must have a 15 or 20 amp branch circuit or you will not be permitted to put a 5-15 or a 5-20 receptacle on it, but even after all that- the AC compressor is not going to be running when an AC tech is pulling a vacuum on it.
 
but even after all that- the AC compressor is not going to be running when an AC tech is pulling a vacuum on it.
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Just playing devil's advocate. I'm not an AC/refrig tech so I don't know if they might be running their recovery unit for some reason while disconnected from the AC unit.

-Hal
 
hbiss said:
Just playing devil's advocate. I'm not an AC/refrig tech so I don't know if they might be running their recovery unit for some reason while disconnected from the AC unit.

-Hal
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Well if they pumped all the refrigerant out of the system there is nothing to compress, and not much load on the compressor if it does run.
 
kwired said:
Well if they pumped all the refrigerant out of the system there is nothing to compress, and not much load on the compressor if it does run.
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AFAIK the compressor is lubricated by oil added to the refrigerant and the motor in a hermetically sealed compressor may be cooled by the same refrigerant, to running it "dry" could be really bad. :happysad:
 
GoldDigger said:
AFAIK the compressor is lubricated by oil added to the refrigerant and the motor in a hermetically sealed compressor may be cooled by the same refrigerant, to running it "dry" could be really bad. :happysad:
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Agree.
Probably kills reciprocating compressors faster than more modern scroll compressors though.
 
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