wire size to heatpump

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  #1  
Old 10-30-01, 03:32 PM
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Question Wire size to heat pump

I recently purchased a house where the previous owner had added on and upgraded the a/c - heatpump unit to a larger size. To me, while using the a/c it never seemed to get as cold as it should and now that the temperatures are getting low enough to turn the heat on I find that not only does it not want to get very hot but that it kicks the breaker often as well. I looked into it and find that it's a 3 1/2 ton unit running on a 6 awg copper wire with a 50 amp breaker. My feeling right away is that the circuit was never upgraded when the heatpump was and that it's been starving for juice to the point of barely working and kicking the breaker when trying to heat. There's a sticker on the front of the air handler that's been partially torn off but from what remains I see that it lists mimum. circuit ampacity as: 83.3/95.4 and max. over current protection: 90/100. Not sure why the numbers are in sequence of two but that's how Rheem lists it. Now, am I right in thinking that instead of a 6 awg copper on a 50 amp breaker I really need more like a 4 awg copper on a 100 amp breaker?

Another thing: the wire coming from the supply box goes to a junction where it splits with wire nuts and goes to the air handler and to the unit outside. Is there a better way than splitting with wire nuts like this or is that common place? For this large of wire I don't think there are wire nuts big enough for 3 4awg. And splitting in this way, would the inside and outside units both need the 4awg as with the main supply line?

Thanks in advance for all help offered,

Glenn
 
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  #2  
Old 10-30-01, 04:28 PM
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Wgoodrich
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The heat pump and the air handler should be ran on separate circuits. I would suspect that if you look in that air handler you should find two 60 amp breakers. Just guessing. Open it up and see. If so then run two 6/2 romex cables to that air handler one to each breaker protected in the panel by a 60 amp breaker each. If you have only one connection and one breaker in that air handler then you should run a 3 awg copper to that air handler and protect it with a 90 amp breaker if you read your name tag correctly. Sounds about right for an air handler with electric heat banks in it using an air to air heat pump outside.

The heat pump also should have a name plate on it with a box saying MCA or minimum circuit ampacity. I suspect you will find it to say 60 amp also. If so then run a 6/2 romex from the panel to that heat pump and protect it on a 60 amp breaker. Be sure that I am right on what the name plate says.

I also suggest that you have a heating company come in and service this heat pump. You may be low on freon. The heat pump is sized right should be able to carry the home without assist heat down to about 30 degrees.

Another trait you might want to know is that a heat pump system does not create an output at your head registers much warmer than room temperature when running on heat pump only. The registers will get warmer when your assist electric heat banks kick in after the thermostat calls for more heat than the heat pump can produce. This is controlled by your thermostat with about a 3 degree varience from desired room temperature and actual room temperature. There is two mecury bulbs in your thermostat, one for your electric heat banks and one for your heat pump.

Come back in if the name plate says different than what I suspected.



Good Luck

Wg
 
  #3  
Old 10-31-01, 08:43 AM
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There's a sticker on the front of the air handler that's been partially torn off but from what remains I see that it lists mimum. circuit ampacity as: 83.3/95.4 and max. over current protection: 90/100. Not sure why the numbers are in sequence of two but that's how Rheem lists it.

You were right in assuming that inside the air handler are two 60 amp breakers. So let me make sure I understand correctly: I run 2 seperate 6/2 ROMEX and use a 120 amp breaker in the box (60 for each side)? Do I use two 6/2 instead of one 6/3 so that they have seperate and equal neutrals to carry the load? Now as for the outside unit, will that be yet a seperate 60 amp breaker, and on this circuit do I run 6/3 ROMEX or what?

 
  #4  
Old 10-31-01, 01:11 PM
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Wgoodrich
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You will need two double pole 60 amp breakers serving the air handler. The breakers inside the air handler need to be matched with exactly the same amp rated and double poles breakers as you see in that air handler. You are running two 220 volt circuits on two separate double pole breakers. One double pole breaker serving each cable. Your white and black of one cable will connect to the first 60 amp double pole breaker in the panel with the bare wire of that cable connected to the grounding bar in the panel. The second cable will connect to its own second 60 amp double pole breaker again connecting the black and white wires to the breaker and the bare wire to the grounding bar in the panel. In the air handler at the other end of those two cables you must connect the black and white of the first cable to the two screws on the 60 amp double pole breaker inside that air handler. The second cable's black and white will connect to the second 60 amp breaker's two screws. The bare wires of both cables will connect to the grounding lug connected to the metal frame of the air handler.

Your heat pump outside will need to be served with its own 60 amp double pole breaker again using a 6/2wGrnd cable wired again the black and white of that heat pump cable to the two screws of the third 60 amp double pole breaker installed in the panel serving that heat pump only. Again the bare wire of that heat pump cable connects to the grouding bar in the panel. The heat pump will require an a/c non fused disconnect outside in sight of the heat pump connecting through that a/c non fused disconnect and to the lugs in the heat pump designed to accept the hot conductors of the cable [being black and white] then the bare wire in that cable again connects to the metal frame of the heat pump. Notice that these cables are using the white wire as a hot conductor creating the 240 volts to serve those appliances. This is allowed due to the fact that both the air handler and the heat pump will not use 120 volts at all or a neutral conductor at all.

Hope this helps

Wg
 
  #5  
Old 10-31-01, 03:26 PM
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This does help - considerably! And thank you a great deal for all your help. One thing left, though: The double pole breakers inside the air handler you spoke of. I looked into this farther because I was getting confused by the fact that the two 60 amp breakers inside the air handler only allow for one connection each. I found on the cover plate of the wire connections where it lists these breakers as Square D series 3 type QOU and they are mounted on a jumper bar assembly QOU14100BAF. Looking closer at this jumper bar assembly I see where the left wire connection goes to both left connections of both breakers via this jumper assembly and the right to both rights the same way. With this new information how does this change the power wires coming in?
 
  #6  
Old 11-01-01, 02:04 PM
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Wgoodrich
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Normally the jumper bar is installed to give you an option allowing you to install parallel 60 amp cables 240 volts each or a single 120 amp cable 240 volts.

Check the name plate and look for the KW rating of that air handler. Then count how many elements are hooked up in that air handler. One element will need to connections for wires. Count the heat elements also. Give us that info then we can get more informed as to what you actually have and what the amp rating required for this electric furnace.

Wg
 
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