15kw heat pump

C

chrismurph214

Member
Location
Royersford, pa
Occupation
Electrician
I’m wiring a15kw heat pump. It has (2) 60amp pre installed breakers in the unit already. The load on the unit at 240v is 62.5 amps. The hvac guy said it’s 80amp electric heat with a 30amp outside unit. Which makes sense when you calculate 15kw at 240v and 1.25% correct? My first question is why the (2) separate 60amp breakers in the unit itself? Should I supply (2) separate feeds to these breakers and breaker them both at the correct size in the main panel at 70amps? Or should I run an 80amp feed to the unit? A little confusing
 
Seemingly the breakers supplied by the HVAC folks serve more as disconnects and are sized at 60 amps (maximum allowed) regardless of the heat strip installed. I've seen 5kw with 60 amp.
Let the nameplate be your guide... MCA, MOCP is what you are interested in.
 
chrismurph214 said:
I’m wiring a15kw heat pump. It has (2) 60amp pre installed breakers in the unit already. The load on the unit at 240v is 62.5 amps. The hvac guy said it’s 80amp electric heat with a 30amp outside unit. Which makes sense when you calculate 15kw at 240v and 1.25% correct? My first question is why the (2) separate 60amp breakers in the unit itself? Should I supply (2) separate feeds to these breakers and breaker them both at the correct size in the main panel at 70amps? Or should I run an 80amp feed to the unit? A little confusing
Click to expand...
Some units have a bar that feeds both breakers and you bring in one feed while other units need 2 feeds. The outside unit should be a different feed altogether.

I think the reason for 2 separate circuits may be two-fold. One it is easier to run 2 smaller cables than one large one and if there is an issue with one circuit you may still be able to use the other circuit and get some heat.
 
augie47 said:
Seemingly the breakers supplied by the HVAC folks serve more as disconnects and are sized at 60 amps (maximum allowed) regardless of the heat strip installed. I've seen 5kw with 60 amp.
Let the nameplate be your guide... MCA, MOCP is what you are interested in.
Click to expand...

Every 5 kw unit I have done were always 30 amps. How can you legally install a 60 amp overcurrent protective device on 5kw unless this is an outside pack unit
 
May be a local thing but almost every, if not every, unit I saw had 60 amp breakers.
As I said, they served as disconnects... the OCP in your supply circuit provided the actual protection.
 
Dennis Alwon said:
Some units have a bar that feeds both breakers and you bring in one feed while other units need 2 feeds. The outside unit should be a different feed altogether.

I think the reason for 2 separate circuits may be two-fold. One it is easier to run 2 smaller cables than one large one and if there is an issue with one circuit you may still be able to use the other circuit and get some heat.
Click to expand...
That’s what I’m thinking Dennis. I didn’t see larger lugs with a bar going to the (2) 60amp breakers. I think it’s more 2 separate feeds. It definitely is throwing me for a loop. Now another question to pick your brain is the 240v at 15kw comes to 62.5 amps. Would you bump up the wire and over current protection at 70amps to allow for the 62.5 or would you
breaker it at 60amps?
 
augie47 said:
May be a local thing but almost every, if not every, unit I saw had 60 amp breakers.
As I said, they served as disconnects... the OCP in your supply circuit provided the actual protection.
Click to expand...
manufacturer is who installed it though.

I have seen same thing but only on occasion. Usually an individual 4.8 kW element will be on a 30 amp breaker though.

I'm working on a new install with geothermal, the 4.8 kW banks are on 25 amp breakers and the 9.6 kW banks are on 50 amp breakers. None of which are accessible without removing both outer cover of appliance as well as an inner cover for the wiring compartment of the heat strip kit.

Compressor, blower, circulating pumps are on their own circuit but no factory installed breaker, breaker size is dependent on size of the motors involved of course.

This seems to be common design for geothermal units regardless what brand they are.
 
augie47 said:
Seemingly the breakers supplied by the HVAC folks serve more as disconnects and are sized at 60 amps (maximum allowed) regardless of the heat strip installed. I've seen 5kw with 60 amp.
Let the nameplate be your guide... MCA, MOCP is what you are interested in.
Click to expand...

augie47 said:
May be a local thing but almost every, if not every, unit I saw had 60 amp breakers.
As I said, they served as disconnects... the OCP in your supply circuit provided the actual protection.
Click to expand...
Correct, just throwing me for a loop because I didn’t see main lugs in the unit to supply the 60s. I only saw 2 60amp breakers marked L one through L4. If I had main lugs with a bar connecting the breakers I’d put my OCP at 80 as per the calculation. maybe it does have a set of lugs and I just missed them. I’m not in front of the unit right now. But I’ve just been raking my brain with this. I fall asleep and wake up with this in my head.
 
chrismurph214 said:
Correct, just throwing me for a loop because I didn’t see main lugs in the unit to supply the 60s. I only saw 2 60amp breakers marked L one through L4. If I had main lugs with a bar connecting the breakers I’d put my OCP at 80 as per the calculation. maybe it does have a set of lugs and I just missed them. I’m not in front of the unit right now. But I’ve just been raking my brain with this. I fall asleep and wake up with this in my head.
Click to expand...
It still is possible and code compliant to run an 80 amp circuit to nearby and then split two "feeder taps" to the unit. I almost never do this for new installs but have done it for when a unit with a single feed got replaced with one not set up for single feed.
 
kwired said:
It still is possible and code compliant to run an 80 amp circuit to nearby and then split two "feeder taps" to the unit. I almost never do this for new installs but have done it for when a unit with a single feed got replaced with one not set up for single feed.
Click to expand...
In your opinion would you just run 2 separate 60amp dedicated circuits. It’s about 15ft from the panel.
 
chrismurph214 said:
I’m wiring a15kw heat pump. It has (2) 60amp pre installed breakers in the unit already. The load on the unit at 240v is 62.5 amps. The hvac guy said it’s 80amp electric heat with a 30amp outside unit. Which makes sense when you calculate 15kw at 240v and 1.25% correct? My first question is why the (2) separate 60amp breakers in the unit itself? Should I supply (2) separate feeds to these breakers and breaker them both at the correct size in the main panel at 70amps? Or should I run an 80amp feed to the unit? A little confusing
Click to expand...
#1
Start with reading 424.22 (B). Over current protection.
48*1.25=60

Read carefully as you get to the lower half of B. Where the subdivided load is less.

#2 then read 424.22 (C). Over current devices.
Key word, supplementary and factory installed.
As you read second paragraph pay attention to the language in the first sentence.

Once you got that move to C. Now you can work on the branch circuit that feed the unit. You under 50 so stop reading. Branch circuit is a key word.

Now move to E.
The first paragraph is what you you need to size the branch circuit.
E applies since you have sub divided load. Do not skip the second sentence in E.

Now read name plate carefully as it may or may not be able to have two branch circuits feeding the unit.
Usually there is a sticker placed on the unit by HVAC if this is a field installed aux heat unit (s). 424.28

FYI. This is a standard test question for those who read. So high light 424.22.

Additional note as you read start off with part 3 article 424.19 then move forward. A applies since you have supplementary over current protection. Again key word: supplementary. So skip 424.19 B.

The key word branch circuit. See 424.3. (B).

When choosing the conductor insulation type see 424.11.
Some AHJ inspectors look for this.
 
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