A/C wiring

[Charlie Bob]

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I'm working on an estimate for a guy, . a new house. he's gonna have a HVAC unit (4 ton) with heat pump. Heat pump is 15kw. . it'll required a 60 amp plus a 30 amp (for blower) circuits. I don't know who's gonna be doing it yet, but i was wondering what,s more common for you all. . .running 2 circuits to it ( 60 amp /6/2 nm and 30 amp 10/2 nm) or a 100 amp disconnect fed with romex.? and do you use SE cable and what size? . . . i see that under table 310.16 you would need #1 wire at 60C. . . Thanks

 

[stevebea]

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I'm working on an estimate for a guy, . a new house. he's gonna have a HVAC unit (4 ton) with heat pump. Heat pump is 15kw. . it'll required a 60 amp plus a 30 amp (for blower) circuits. I don't know who's gonna be doing it yet, but i was wondering what,s more common for you all. . .running 2 circuits to it ( 60 amp /6/2 nm and 30 amp 10/2 nm) or a 100 amp disconnect fed with romex.? and do you use SE cable and what size? . . . i see that under table 310.16 you would need #1 wire at 60C. . . Thanks

Does the heat pump have breakers mounted in it where the field wiring terminates?

 

[Gac66610]

it depends on the termination lugs, is there an option to just run one larger wire to feed all fuses/breakers in the furnace or does it need two separate runs
i run the 6-2 nm and 10-2 nm .... but thats me

 

[Charlie Bob]

it depends on the termination lugs, is there an option to just run one larger wire to feed all fuses/breakers in the furnace or does it need two separate runs
i run the 6-2 nm and 10-2 nm .... but thats me

That's what i was gonna run. . . the house is just being built, he don't even know who is gonna do the HVAC yet, so there's no unit yet either. . i was just trying to figure ny end. i was just curious since i w3as told by a HVAC guy this morning that they sometimes have electricians run a 100 amp disconnect to ti, and then they feed their end from it. . . i was curios as to what would be the proper size NM, i imegine SE in this case, to run....

 

[texie]

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I'm working on an estimate for a guy, . a new house. he's gonna have a HVAC unit (4 ton) with heat pump. Heat pump is 15kw. . it'll required a 60 amp plus a 30 amp (for blower) circuits. I don't know who's gonna be doing it yet, but i was wondering what,s more common for you all. . .running 2 circuits to it ( 60 amp /6/2 nm and 30 amp 10/2 nm) or a 100 amp disconnect fed with romex.? and do you use SE cable and what size? . . . i see that under table 310.16 you would need #1 wire at 60C. . . Thanks

If it was my call, I would not rough anything without a detail set of specs on the unit. Without specs itis just a WAG and I'm a stickler about that because it will always come back as your problem if it is wrong. I'm assuming we're talking about the AHU and the condensing unit will be a separate discussion. As others said, it may have it's own breakers to sub divide the load or it may need two branch circuits. If it takes 2 branch circuits, I would run a feeder of the appropriate size, to the unit and put a 6 space panel there and the breakers can be your disconnects.

 

[Charlie Bob]

If it was my call, I would not rough anything without a detail set of specs on the unit. Without specs itis just a WAG and I'm a stickler about that because it will always come back as your problem if it is wrong. I'm assuming we're talking about the AHU and the condensing unit will be a separate discussion. As others said, it may have it's own breakers to sub divide the load or it may need two branch circuits. If it takes 2 branch circuits, I would run a feeder of the appropriate size, to the unit and put a 6 space panel there and the breakers can be your disconnects.

some of this people here build a house going by a sketch. . i'm seriuos. i was just trying to put my estimate together for now. . and then worry about the installation in due time.

 

[John120/240]

What do the economics say as to cheapest method ? One wire & panel vs multiple wires ?

Realiability ? Figure the cost & options. Good Luck

 

[rltomkinson]

Without knowing which you will need to provide, I would give them the price for the more expensive option.

If it's a competitive bid, price the lower and give the other as an option.

 

[220/221]

some of this people here build a house going by a sketch. . i'm seriuos. i was just trying to put my estimate together for now. . and then worry about the installation in due time.

A sketch is fine as long as it shows the basics. Estimating based on what you have provided is just dumb.

A 4 ton split system heat pump needs a 240V 35-40A circuit for the condenser and a 240V 15 amp circuit for the air handler.

A 4 ton package unit heat pump will ned a 40A 240V circuit.

Judging from a couple of your posts, you may be talking about heat strips. I'm not even gonna guess.

 

[kwired]

Judging from a couple of your posts, you may be talking about heat strips. I'm not even gonna guess.

That is what I figured also from what was said.

Be careful about connecting 6-2 NM cable just because the breaker in the unit is a 60 amp breaker.

NM cable must be sized according to the 60?C ampacity table. 6 AWG is good for 55 amps.

You can use next size higher standard overcurrent device if minimum ampacity needed is less than 55 amps.

It is easy to overlook this one. If the heater is 10kW @ 240 volts it should draw about 42 amps. Minimum conductor size will be 125% of 42 = 52.5. If there is no blower on same circuit you are ok, you are still under 55 amps maximum for a 60?C conductor, if there is a blower on the circuit it could put you over 55 amps but would have been acceptable on a 75?C conductor with a 60 amp breaker.

Many heat strips are only 9.6 kW and not actually 10 kW. this gives you a little more leeway for adding a blower and not exceeding the 55 amp limit - but you may want to double check before just running a 6-2 NM cable.

 

[augie47]

kwired hit the nail on the head.
There is rarely a week that goes by that I don't encounter a HVAC unit with undersized conductors, more so after the Code reduced SE to the 60? rating.
Heat and air installers around here have historically used $6 and #10, but as kired points out, that's not always sufficient. I had a 15 kw unit the other day with one MCA at 34 and the other at 59 amps. I have also had 15 kw units wuth a single circuit MCA of 104.
If you have no firm data, I'd see if it was reasonable to install conduit and pull conductors later, or to CYA, I'd install a feeder with greater than a 104 amp rating.