max breaker size for #6 wire

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  #1  
Old 03-26-06, 12:16 PM
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max breaker size for #6 wire

Hello all,

Thanks for the great information available on this forum.

I would like to know the largest breaker size for a subpanel fed with #6 wire. I plan on a heat pump with a RLA of 40 amps, a 1hp pool pump, a 3 hp pool pump, and a 20amp circuit for oulets and lights. I was hoping a 70 amp breaker would do it. The panel is 100' from the main panel.

Thanks
 
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Old 03-26-06, 12:40 PM
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You cannot put #6 on a 70 amp breaker unless it is THHN/THWN conductors in conduit the whole way.
I myself would use #4cu (or #2al) on a 100 amp breaker for this sub-panel.
 
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Old 03-26-06, 01:06 PM
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I would like to know the largest breaker size for a subpanel fed with #6 wire. I plan on a heat pump with a RLA of 40 amps, a 1hp pool pump, a 3 hp pool pump, and a 20amp circuit for oulets and lights. I was hoping a 70 amp breaker would do it. The panel is 100' from the main panel.


All your pumps are 220V single phase, correct? What size is your main electric service? 200 A--
I aswell would go with a 100 A sub. Pipe it and use copper THHN, for longevity. The outrages prices
we now pay for the wire is due more to the petrolium products used for the insulation, rather than the metals themselfs. If you can swing it, go for it. The over all price difference (wire, equip.etc)
is minimum.
 
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Old 03-26-06, 01:06 PM
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My situation is I already have #6 out to the spot. I took out a hot tub and want to add the items I mentioned. Is that enought to run those items I mentioned?

Thanks
 
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Old 03-26-06, 01:12 PM
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Well that does change things some. What is the wireing method in use now for the #6s? Is it pipe, what size? How many conductors to the location? Get the FLA ratings of all the motors and voltages.
 
  #6  
Old 03-26-06, 01:32 PM
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If you want all that equipment to run at the same time, your existing #6 probably won't suffice.

If you use #4 feeder and a 100A panel, you'll have capacity now and in the future.

Of course, you'll need larger conduit which mean digging it up.
 
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Old 03-26-06, 01:43 PM
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It is #6x3 w/ground through the attic, then piped about 50' to the location. The 1hp is about 8amps and the 3 I will have to check on. Probably 12-15 amps.
 
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Old 03-26-06, 01:44 PM
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220vt motors. 3/4" pipe
 
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Old 03-26-06, 02:06 PM
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That #6 is only good for 60 amps MAX.
 
  #10  
Old 03-26-06, 02:14 PM
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Yeah, I know I'm pushing it. Maybe I will go for a gas heater instead of a heat pump.
 
  #11  
Old 03-26-06, 02:16 PM
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The ampacity of 6/3 NM is 55A, and that is presuming no thermal derating for the attic run. IMHO this cable is barely enough to run the heat pump once you consider the attic temperature. If your calculated load is less than 55A, and there is no derating, then you may protect this wire with a 60A breaker.

The total of all the loads that you describe rather exceeds 70A. You will need to replace this feeder to run all of the loads that you describe.

You may be able to re-use the 'pipe' itself to carry the new conductors, however it will be dicey. You will need to determine _exactly_ what type of conduit it is, and the exact 'trade size'. This is because different types of conduit have different internal areas for the same 'trade size'. Also 'trade size' is only loosely related to the actual diameter, for example 'trade size 1/2" EMT has roughly a 3/4" outer diameter.

-Jon
 
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