Branch Circuit for Heat Pump Outdoor Unit

[chad51]

Hello. This is my first post and I apoligize if this question has been answered somewhere else.

Installation of a 2.5 ton split system heat pump. Breaker box on one end of house, approximately 40 feet, from other end where air handler will be with 15kw electric heat. Outdoor unit approximately less than 30 feet (line set length) from air handler. Air handler to be fed by 2 runs of 6-2 w/ground on 60 amp breakers in main panel. From the air handler, I would like to feed outdoor unit from circuit which only has the 5kw of electric heat on it. Both breakers on heater package are 60 amp breakers.

Question: Can I run a branch circuit from load side of 60 amp breaker which serves only 5kw in air handler to outdoor unit using 10/2 w/ground, and install a outdoor disconnect with a 30 amp breaker as the OCPD at the outdoor unit? Optionally, if a make the circuit a tap circuit and pick up power from line side of 60 amp breaker, would I have to continue with the 6-2 w/ground to the outdoor disconnect or can I still use the 10-2 w/ground, providing I'm less than 25 feet?

By what I've read about wire/breaker sizing for HVAC, it seems I'd would be in code even if I didn't use the 30 amp breaker at the outdoor unit in the branch style circuit, but I wanted to have the recommended OCPD of the manufacturer.

Thanks for any suggestions.

 

[charlie b]

This appears to me to be a task that should be done by an electrician, not by an HVAC specialist. If you are not licensed to perform electrical work in your area, then our forum rules would not allow us to assist you. Have I misunderstood the information you put in your profile?

 

[kwired]

2.5 ton - possibly calls for 30 amp breaker - some could ask for 35 amp max but likely will never trip a 30.

Will heat strip be allowed to run while heat pump runs? If not put them both on 30 amp feed.

I personally think even if the heater and compressor run simultaneously for defrosting only, it will not run long enough to trip breaker, but still may not be a wise choice to install this way, just in case it does not hold.

 

[Little Bill]

This appears to me to be a task that should be done by an electrician, not by an HVAC specialist. If you are not licensed to perform electrical work in your area, then our forum rules would not allow us to assist you. Have I misunderstood the information you put in your profile?

Charlie, obviously I can't answer for the OP, but in certain areas, HVAC techs are allowed/licensed to install the electrical associated with the HVAC equipment.

 

[sgunsel]

If the heat pump is located in a region where outdoor temperatures go below 30F, or something like that, the resistance heaters come on with the heat pump whenever it can't supply enough heat on its own. If a heater is present, sooner or later it will run, and it very well could run continuously (more than 3 hours). I had a heat pump in northern Ohio for about 11 years, and on cold winter days, the heat pump and resistance heater would run without stopping. I actually had two resistance heaters in the air handler, but kept one turned off to prevent the electric meter from "overheating". The utility loved it - we were on demand billing and the more we used, the more we paid. They also conveniently read the meter every other month to be sure the highest possible peak demand would register.

 

[david luchini]

Question: Can I run a branch circuit from load side of 60 amp breaker which serves only 5kw in air handler to outdoor unit using 10/2 w/ground, and install a outdoor disconnect with a 30 amp breaker as the OCPD at the outdoor unit?

No, you cannot tap the 60A branch circuit in this manner. Per 240.21(A), branch circuit taps must meet the requirements of 210.19 and 210.20.

Optionally, if a make the circuit a tap circuit and pick up power from line side of 60 amp breaker, would I have to continue with the 6-2 w/ground to the outdoor disconnect or can I still use the 10-2 w/ground, providing I'm less than 25 feet?

Tapping ahead of the 60A branch circuit breaker would be a feeder tap. In order to know if the 10-2 conductor size was OK for a tap not over 25 feet long, you'd have to know the size of the feeder OCPD upstream. See 240.21(B)(2).

By what I've read about wire/breaker sizing for HVAC, it seems I'd would be in code even if I didn't use the 30 amp breaker at the outdoor unit in the branch style circuit, but I wanted to have the recommended OCPD of the manufacturer.

If I understand you correctly, yes you could use #10 wire with a 40A c/b if the manufacturer listed an MCA of 30 and an MOCP of 40.

 

[charlie b]

This thread was temporarily moved to an area accessible only to the moderators, while the question of whether the OP was qualified to perform electrical installation work was investigated. I have since learned that the OP is a licenced electrician, and am therefore restoring this thread to the open discussion area. I apologize to the OP for the delay and inconvenience.

 

[dkidd]

Charlie, obviously I can't answer for the OP, but in certain areas, HVAC techs are allowed/licensed to install the electrical associated with the HVAC equipment.

Some of them shouldn't be. I had one replace an existing outdoor condensing unit. The unit nameplate said MOCP 25 amp. The old unit was fed from a 35 amp breaker. When I pointed it out to them, I was told that it was an existing condition, and they didn't have to change it.

 

[augie47]

At first read, I question the 60 amp OCP for the 5 kw strip. All of the airhandlers I have inspected have required an OCP far less than 60
for the 5 kw heat strip (either at the panel or at the unit).
Over looking that, as long as you complied with the 240.21 tap rules, I see not problem with your feeding the outdoor unit.

 

[Little Bill]

Some of them shouldn't be. I had one replace an existing outdoor condensing unit. The unit nameplate said MOCP 25 amp. The old unit was fed from a 35 amp breaker. When I pointed it out to them, I was told that it was an existing condition, and they didn't have to change it.

I won't express my opinion about whether they should or shouldn't be allowed to install the electrical. I was only pointing out that in some areas they are allowed to.

 

[kwired]

If the heat pump is located in a region where outdoor temperatures go below 30F, or something like that, the resistance heaters come on with the heat pump whenever it can't supply enough heat on its own. If a heater is present, sooner or later it will run, and it very well could run continuously (more than 3 hours). I had a heat pump in northern Ohio for about 11 years, and on cold winter days, the heat pump and resistance heater would run without stopping. I actually had two resistance heaters in the air handler, but kept one turned off to prevent the electric meter from "overheating". The utility loved it - we were on demand billing and the more we used, the more we paid. They also conveniently read the meter every other month to be sure the highest possible peak demand would register.

This is more likely a problem when you turn the thermostat up a few degrees and it demands the back up heat to help with bringing room temperature up quicker.

If it is cold enough that the heat pump can't keep up it is moving little heat and is not loaded very much. It is a good idea to install a lockout thermostat to lock out the heat pump when it is cold enough it is no longer efficient to operate it. Some electronic indoor thermostats have a place to connect an outdoor probe and can be programmed to lock out the heat pump when it is too cold outside.

If you turned off some of the heat to keep peak demand down, you probably have a little trouble keeping up on some of the coldest days, if not, you may have an oversized system.

 

[kwired]

At first read, I question the 60 amp OCP for the 5 kw strip. All of the airhandlers I have inspected have required an OCP far less than 60
for the 5 kw heat strip (either at the panel or at the unit).
Over looking that, as long as you complied with the 240.21 tap rules, I see not problem with your feeding the outdoor unit.

Thing is the 10kw strip is nothing more than two of the same components used in the 5 kw strip and those are protected with 50 or 60 amps normally. Usually 50 if strip only, and 60 if the blower happens to be on same circuit. The 5kw strip could be protected with 25 amps and no problems but most units are labeled 30, don't really know why.

 

[augie47]

Thing is the 10kw strip is nothing more than two of the same components used in the 5 kw strip and those are protected with 50 or 60 amps normally. Usually 50 if strip only, and 60 if the blower happens to be on same circuit. The 5kw strip could be protected with 25 amps and no problems but most units are labeled 30, don't really know why.

I agree and from the way I read the OP it sounded as if it (the 5kw strip) was protected by a 60. I was pointing out (or attempting to) the possible violation.

 

[Mgraw]

The OP says the heater package comes with two 60 amp breakers. That would seem to indicate a 20 kw heater. A 15 kw usually has a 60 and a 30 amp breaker. If the heater is 20kw then I would say no to tapping the condenser circuit. If the heater is 15kw then I would say the heater has the wrong breaker.

My guess would be OP bought a 20kw heater and only needs 15kw. Now he wants to disconnect one strip and tap the condenser circuit.

 

[augie47]

May be different there, but in this area, the air handlers with built-in breakers and two strips always come "factory" with two 60 amp breakers.
The installer can adjust accordingly depending on the strips he installs or he may elect to use the manufacturer MOCP at the panel and uses the 60s purely as disconnects.
It is not uncommon here for HVAC techs to ignore the MOCP ratings on the air-handlers.

 

[kwired]

Most that I have seen more recently the air handler is a separate purchase item from the heat strip. If you purchase air handler only there is no breaker(s). Add heat strips and the appropriate breakers are included with the kit. The kit has a molded plug that the original supply for the air handler plugs into which connects it to one of the breakers in the heat strip kit.

I have had to install many heat strips, or at least finish connecting them because I was ready to connect and the HVAC guy didn't have it done yet.

I really don't see a code violation in connecting the 5 kw strip to a 60 amp breaker unless the nameplate states a maximum overcurrent device of less than that. Normally I would not have a desire to run 60 amp conductors when 30 amp would be sufficient so it would not end up on 60 anyway.

OP could always install a 4-6 circuit panel and separate it from there, or even run a 100 amp feed to it and then all three branch circuits from that point. Although I think he was going to have some difficulty doing so is why he asked in the first place.

 

[renosteinke]

I am a little confused by the vocabulary.

The OP says 'split system,' which to me means a system where the outside unit pipes refrigerant to independently mounted fan units scattered around the interior. An "air handler,' on the other hand, describes to me something associated with ductwork. The two systems don't exist together.

What am I missing? How does the air handler relate to the split system?

 

[dkidd]

Most split systems consist of an outdoor unit and one indoor, the typical residential sysstem. The indoor unit is an air handler.

 

[Mgraw]

May be different there, but in this area, the air handlers with built-in breakers and two strips always come "factory" with two 60 amp breakers.
The installer can adjust accordingly depending on the strips he installs or he may elect to use the manufacturer MOCP at the panel and uses the 60s purely as disconnects.
It is not uncommon here for HVAC techs to ignore the MOCP ratings on the air-handlers.

I guess it is different here. Usually the breakers are part of the heater kit. Those with breaker kits come with 1 two pole 60 for 10kw, 1 two pole 60 amd 1 two pole 30 for 15 kw, and 2 two pole 60s for 20kw. Never had a 15 kw with 2 two pole 60s.

 

[kwired]

I guess it is different here. Usually the breakers are part of the heater kit. Those with breaker kits come with 1 two pole 60 for 10kw, 1 two pole 60 amd 1 two pole 30 for 15 kw, and 2 two pole 60s for 20kw. Never had a 15 kw with 2 two pole 60s.

Maybe in the OP they made a mistake at the assembly plant and that is why there are two 60's.