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Old 05-22-2009, 09:03 PM   #1
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I'm installing a 4 ton RHEEM heat pump system. I "hired" a guy to do it for me, and he came out here and wanted paid in cash up front, so I told him to hit the road. Sheetrock starts Monday and I can't figure something out after reading all the books. I'm more than qualified to hook it up, just need to know the requirements. I used to own an electrical business.

Does the outside unit need a dedicated circuit? It calls for 50 amps. Or can I just branch that off of one of the two 60 amp circuits feeding the air handler/backup heat. It's a 20 kW heat strip. I just can't imagine why I'd need more than 120 amps for the whole system. Never had a heat pump. Does the outside unit ever run when it kicks on the emergency 20 kW heat strip? If not it seems like I just need to branch off from there and use it. FYI I'm about out of spots on my electric panel so don't want to use them if not necessary. Thanks in advance!

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Old 05-22-2009, 09:44 PM   #2
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There should be a listing on the unit min. max circuit protection.I don't run the electrical but I think they have their own circuit

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Old 05-22-2009, 09:53 PM   #3
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Originally Posted by TheGrinch View Post
I'm installing a 4 ton RHEEM heat pump system. I "hired" a guy to do it for me, and he came out here and wanted paid in cash up front, so I told him to hit the road. Sheetrock starts Monday and I can't figure something out after reading all the books. I'm more than qualified to hook it up, just need to know the requirements. I used to own an electrical business.

Does the outside unit need a dedicated circuit? It calls for 50 amps. Or can I just branch that off of one of the two 60 amp circuits feeding the air handler/backup heat. It's a 20 kW heat strip. I just can't imagine why I'd need more than 120 amps for the whole system. Never had a heat pump. Does the outside unit ever run when it kicks on the emergency 20 kW heat strip? If not it seems like I just need to branch off from there and use it. FYI I'm about out of spots on my electric panel so don't want to use them if not necessary. Thanks in advance!

Yes you need a dedicated out side (Condenser) circuit. 40 amp

The air handle will need two dedicated circuits. If you have a 20kw heat strip here is the math

20000 watts divided by 220 (volts) equals 90 amps.

If you are out of spaces on the load center you may be able to replace individual 110 breakers with twin breakers.

Also all the ablove is CODE.

What size wire are you using for the air handle and condenser?

So, what did you do in a electrical business?

Last edited by Plumber101; 05-22-2009 at 09:57 PM.
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Old 05-22-2009, 09:58 PM   #4
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i would think local codes would trump any answer your going to get on here. can it be done sure have i seen it done rarely i would think its cheaper to run several smaller gauge wires than one massive or two massive wires and as far as running out of space in your panel, can you say piggyback breakers or subpanel? sure i knew you could elec heat does run with heatpump in very cold conditions. it depends on how the low voltage is wired as to how much backup heat will operate in conjuntion with the heatpump
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Old 05-22-2009, 10:07 PM   #5
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Quote:
Originally Posted by kennzz05 View Post
i would think local codes would trump any answer your going to get on here. can it be done sure have i seen it done rarely i would think its cheaper to run several smaller gauge wires than one massive or two massive wires and as far as running out of space in your panel, can you say piggyback breakers or subpanel? sure i knew you could elec heat does run with heatpump in very cold conditions. it depends on how the low voltage is wired as to how much backup heat will operate in conjuntion with the heatpump
Several smaller wires...What! Do it right or I will see you on the 6 o'clock news about the family that died from that electrical fire

Piggy back..Last I knew only Square D that had a breaker that could be double tapped. Not worth it. Breakers trip on heat and over load conditions

Yes, you can stage the heat elements with outside stats
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Old 05-22-2009, 10:14 PM   #6
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Thanks all. I see it takes 45-50 amps for the condenser/pump, so it needs its own circuit. Hope the 200 amp service can take it all.

There are no codes here.

I owned an electronics shop. Now I'm a transmission line engineer. Probably why I have so many questions
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Old 05-22-2009, 10:29 PM   #7
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yes thats right several as in more than2 and less than 4 two he will need for the ahu and the one needed for the outdoor unit rather than running one basically that will need to be the size of the wire that feeds his house yes breakers trip on heat o/l conditions so whats your point? if it aint overloaded it shouldnt be overheated
Quote:
Originally Posted by Plumber101 View Post
Several smaller wires...What! Do it right or I
will see you on the 6 o'clock news about the family that died from that electrical fire

Piggy back..Last I knew only Square D that had a breaker that could be double tapped. Not worth it. Breakers trip on heat and over load conditions

Yes, you can stage the heat elements with outside stats

Last edited by kennzz05; 05-22-2009 at 10:33 PM. Reason: because a terd chaser called me on it
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Old 05-22-2009, 11:42 PM   #8
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Quote:
Originally Posted by TheGrinch View Post
I'm installing a 4 ton RHEEM heat pump system.
4 tons = 48,000 BTU/hr = ~5kW = 21A.
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Old 05-23-2009, 12:42 AM   #9
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Quote:
Originally Posted by kennzz05 View Post
yes thats right several as in more than2 and less than 4 two he will need for the ahu and the one needed for the outdoor unit rather than running one basically that will need to be the size of the wire that feeds his house yes breakers trip on heat o/l conditions so whats your point? if it aint overloaded it shouldnt be overheated
Point is Over loaded and over heated are two completely different things

Ever wonder why sometimes a lock compressor and draws 90+ amps won't trip the breaker but trips therm-overload n the compressor?
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Old 05-23-2009, 10:27 AM   #10
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Quote:
Originally Posted by Plumber101 View Post
Ever wonder why sometimes a lock compressor and draws 90+ amps won't trip the breaker
but trips therm-overload n the compressor?
Because the trip curve of the t'overload is quicker than the trip curve of the breaker?
Because the t'overload is already hot and so trips prematurely?
Because. . .?
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Old 05-23-2009, 11:19 AM   #11
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It is a good thing to run separate circuits. Then if a breaker trips (usually to the outside condenser unit), you know that is where the trouble is.

So helps with troubleshooting.

Also you say there are no codes in your area... But anyway a good thing to have is an "in-sight disconnect" or "lockout breaker" for appliances which might need to be worked on by a serviceman. This is a work safety thing for the serviceman.

With this, the serviceman can see that the power is off (because he can see it from where he is working) or can place a lock on the breaker so no one can come along and turn on the breaker while he is working.

They look like this...

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Old 05-23-2009, 11:21 AM   #12
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Wow, what a mess up thread.


Plumber, just for information, yes you can parallel feed the heat strip with the condensor, as long as it is not a heat pump where they will be running simultaneously, and as long as the circuit requirements are the same. So basically this idea IS ruled out as it is a heat pump and will likely require a much smaller circuit than 60.
Also, we use 240v in figuring circuits. THAT is code, not "220".


Grinch, "it takes 45-50 amps" does not cut it. What is the actual information from the rating plate on the unit?
Tell us the minimum circuit ampacity, and the maximum fuse/breaker size.
As Yoyizit said, this unit will draw 20 something amps and likely require a 30 or 40 amp circuit.
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Old 05-23-2009, 12:03 PM   #13
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Quote:
Originally Posted by kennzz05 View Post
i can it be done sure have i seen it done rarely i would think its cheaper to run several smaller gauge wires than one massive or two massive wires
Quote:
Originally Posted by kennzz05 View Post
yes thats right several as in more than2 and less than 4
Only size 1/0 AWG and larger may be run in parallel, except for certain control functions:

2008 NEC:

310.4 Conductors in Parallel.


(A) General.
Aluminum, copper-clad aluminum, or copper

conductors of size 1/0 AWG and larger, comprising each
phase, polarity, neutral, or grounded circuit conductor shall
be permitted to be connected in parallel (electrically joined
at both ends).
Exception No. 1: Conductors in sizes smaller than 1/0
AWG shall be permitted to be run in parallel to supply
control power to indicating instruments, contactors, relays,
solenoids, and similar control devices, or for frequencies of

360 Hz and higher, provided all of the following apply: ....
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Old 05-23-2009, 12:16 PM   #14
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Willis, I actually posted something similar and removed it after re-reading what he wrote.

I think he means running a separate circuit for each thing. I don't think he means running conductors in parallel.

See what you think.
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Old 05-23-2009, 12:18 PM   #15
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The info on the nameplate is the only way to properly connect the unit. You'll need two things.

1) Minimum circuit ampacity. This is the smallest wire that can be run. It is sized according to table 310.16 in the codebook. 75C column. (60C column if it's NM cable) The #14/15 amp, #12/20 amp, and #10/30 amp requirements do not apply. You can install larger wire, not smaller.

2) Maximum breaker or fuse size. Sometimes this is listed as 'maximum OCPD'. (Overcurrent Protective Device). This is the maximum breaker that can be installed. You can install a smaller breaker, not larger.

This is one of the few times it's perfectly legal to have a breaker that's too big for the wire. Unfortunately, not a lot of inspectors know this, and more than a few of them are less than willing to accept code instruction from a dumb 'ol electrician.

If you don't have the info from the unit, you're completely safe with a #8/2. It's most likely overkill, but it's better than replacing it after the walls are done. The other way I usually go is figure 1 ton = 1 HP, and use the motor current/wire size from table 430.248 or 430.250. If it's close, go one size up.

Rob

P.S. As Petey said, it's OK to tap one of the strip heat circuits, but only if the condenser and strip heat cannot operate at the same time, and only if the circuit tapped meets #2 above. Most of us just run a separate circuit though.

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