Air conditioner electrical setup

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  #1  
Old 03-21-15, 10:25 PM
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Air conditioner electrical setup

Hello,

I have four 1000w light ballasts and an air conditioner that I'm trying to get hooked up. The air conditioner requires 240v with a maximum breaker fuse of 20 amps. The ballasts are also rated for 240v, and I hope to have them affixed to a timer. The timer I have in mind is rated for 30 amps, and would handle all four ballasts simultaneously. I have an existing length of 8-3 wire (affixed to a 50 Amp Type QP Double-Pole Circuit Breaker) running into the room. I attached a schematic to help visualize the setup. Ignore the 120v section, and everything in red.

My dilemma is that I need a 20 amp 240v breaker for the A/C, and a 30 amp 240v breaker for the timer. There are no slots left in the breaker box for any additional breakers. Is there a way to utilize the existing 8-3 wire for both the A/C and the timer? Can I split the 50 amp breaker into a 20 amp and 30 amp one, but use the same 8-3 wire to feed both? Or will I have to pull a separate wire through the wall? Any help with this would be greatly appreciated! Thanks!

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  #2  
Old 03-22-15, 03:59 AM
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Welcome to the forums! I can't imagine a timer alone requiring a 30 amp circuit. Maybe that is the maximum it will handle. Can you post the make and model of the timer so we can investigate it further? Why do you want the lights and the air conditioner on the same timer? Is this in a separate building from your house? If so, have you installed a sub panel to handle this in that building?
 
  #3  
Old 03-22-15, 05:11 AM
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How long will the lights be on? You are looking at 17 or 21 amps of light, depending on if this is continuous or not.
 
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Old 03-23-15, 09:47 AM
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It looks pretty simple to me. Install a 60 amp subpanel and from that feed the air conditioner circuit from a 20 amp 2 pole breaker and the timer with a 30 amp 2 pole breaker.
 
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Old 03-23-15, 10:22 PM
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What is the amp draw of your ballasts? How many hours do you plan on running these a day? Also, how big of a room do you have that you need 4 1,000W lights?
 
  #6  
Old 03-24-15, 11:59 AM
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He won't be able use that 8/3 for a sub panel,that would be the best plan but a new feeder will be required.
Geo
 
  #7  
Old 03-26-15, 01:51 PM
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Hello all, thank you for your responses. The timer handles all four of the 1000w lights simultaneously. It is a Powerbox DPC-4000-240V-​4HW (30Amp, Four 240V Outlets) Hardwire 4 Wire.

Two of the ballasts say that the max current is 9.5 amps. But they are able to run on 120 or 240v, so I imagine that figure is if they are running on 120v. The other two ballasts are 240v dedicated and require 4.6 amps.

I don't want the A/C on the same timer as the lights, I just want it powered by the same feeder wire, since the 8-3 wire is already in place. It's not a separate building from my house, but I'm trying to minimize unnecessary work. The lights will be on for most of the day, 18 hours max.

I have since purchased the 60 amp subpanel, and the 30 and 20 amp 2 pole breakers. I understand that the max rating for 8-3 wire is only 40 amps, and that I'm using a 50 amp breaker at the main, but does it change anything that my load will never be above 40 amps? (9.5 + 9.5 + 4.6 + 4.6 + 8.35 = 36.55 amps). Do I really need to replace this 8-3 with 6-3?

A gentleman at the local hardware store recommended that I hook up the 8-3 feeder wire to a 50 amp breaker in the subpanel, as a main disconnect (he said to run the two hot wires into the 50 amp breaker in the subpanel, not directly to the lugs). I imagine that this is just for an extra point of protection?

Thanks again for your help.
 
  #8  
Old 03-26-15, 02:03 PM
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You can leave the #8-3 in place, but it should not have a feeder breaker larger than 40A. If you need the 50A breaker, then yes the wire must be #6 or larger (in which case you could actually do 60A). Your statement of the load never exceeding 36A is based on the assumption that none of your devices ever malfunction, melt-down, etc, i.e. when you really need a breaker to work properly.

A "main" breaker is only required in the subpanel if you have more than 6 total breakers in the panel.

My assumption Is that the existing cable type "NM-B" given that you're calling it 8-3? Are you sure of that?
 
  #9  
Old 03-26-15, 04:45 PM
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This is what the wire looks like coming out of the wall, if it helps any. Could it be 6-3? If it's 8-3, and I decide to swap out the feeder breaker at the main panel to a 40A, will it still be able to run the subpanel with 30A and 20A breakers (if the total current of the load is only 36A)? Thanks for all of your help.

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Last edited by silent_bob; 03-26-15 at 05:05 PM.
  #10  
Old 03-26-15, 04:59 PM
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That is 8-3 w/ground or 6/3 w/ground. It should be stamped/printed on the black jacket.

Looks more like 8-3 in the picture.
 
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Old 03-26-15, 08:54 PM
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Assuming it is 8/3, if I decide to swap out the feeder breaker at the main panel to a 40A, will it still be able to run the subpanel with 30A and 20A breakers (if the total current of the load is only 36A)? Thanks!
 
  #12  
Old 03-27-15, 06:35 AM
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Yes you can do it. The 40A breaker probably won't trip at that level.
 
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