Subpanel or individual circuits for kitchen

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  #1  
Old 09-29-13, 01:28 PM
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Subpanel or individual circuits for kitchen

I'm planning the electrical work for the kitchen, and would appreciate some advice on what to do. I have 6 circuits that I need to route from the panel to the kitchen, which is about 60ft.

1x 50A (240V)
1x 30A (240V)
4x 20A (120V)

My original plan was to run THHN in 2 EMT conduits (1" + 3/4"). The main headache is the 50A circuit (I hate thick wires!), which I think needs 6AWG.
But, in reviewing derating and fill tables, it appears that I might do better (save a bunch of effort and wires), if I just do a subpanel close to the kitchen.


Plan #1: Individual circuits

The 1" conduit would carry the two 240V circuits:
  • 4x 6AWG (2 hot + neutral + ground)
  • 3x 10AWG (2 hot + neutral)
The 3/4" conduit wouuld carry the rest:
  • 9x 12AWG (4 hot + 4 neutral + ground)
I used fill calculators, and they all came <40%, and I think I'm staying under the 70% derating categories.

If I go with this, does anyone see anything wrong with this design?


Plan #2: Subpanel
It then occurred to me that if I had to run 6AWG anyway, I might be able to get away with just that for *all* the circuits if I just put them on a subpanel. If I don't have to derate at all, I think 6AWG THHN is good for 75A. I'd run them to a subpanel, with a 70A breaker at the main.

Is this workable?

I think 70A is sufficient for all these circuits since most of them are really overkill for what they're used for. One concern is that my main panel already feeds another 60A subpanel to somewhere else. Is it permissible to add another 70A subpanel in this case?

Thanks a lot for any advice!

Cheers.
 
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  #2  
Old 09-29-13, 02:21 PM
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You would need to do a load calculation to see if the 70 amp feeder is large enough. I don't think it is.

If you use 12-3 you only need two runs back to the panel plus the 30 and 50 amp runs.
 
  #3  
Old 09-29-13, 05:35 PM
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I'm not a big fan of remote-located subpanels in residential situations. I find that it gets confusing as to where a circuit terminates for a savings of a few feet of wire.

I would probably run NM-B for all the circuits and ditch the EMT plan. Granted, EMT will look all nice and clean, but it'll probably be covered up anyway. As pcboss pointed out, running 4 cables 60' seems like the way to go.

As for your question though, you can add another subpanel if you want. But the kitchen is a high-draw location. I wouldn't want to risk tripping a breaker when cooking Thanksgiving dinner.
 
  #4  
Old 09-29-13, 05:52 PM
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Thanks, guys! I was a bit hesitant about the subpanel too, because of the high load. I'd like to run NM-B, but I don't think I can do that over most of that route (~60ft), since it has to go through an unfinished garage, and an accessible crawl space*.

I used an online load calculator and it came up with an amperage of 51A.

And just to make sure I'm understanding everything correctly, is it true that I can use 6AWG for 75A (and 12AWG for 30A), if I only have 3 CCC in a conduit?


* I've never figured out how code applies to my crawl space because it's *very* accessible. My house is split-level, so you can literally walk from the garage into the crawl space (it's ~4ft high), and I use it for storage. There are some old lights in the crawl space whose circuits were routed in EMT, but I'd love it if code lets me run romex.
 
  #5  
Old 09-29-13, 06:51 PM
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#12 is limited to 20 amps by Article 240. The #6 is only good for 60 amps.
 
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Old 09-29-13, 07:02 PM
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And just to make sure I'm understanding everything correctly, is it true that I can use 6AWG for 75A (and 12AWG for 30A), if I only have 3 CCC in a conduit?
I wouldn't protect the #6 any higher than 60 amps and the #12, that has to be protected at 20 amps by the NEC.

I've never figured out how code applies to my crawl space because it's *very* accessible. My house is split-level, so you can literally walk from the garage into the crawl space (it's ~4ft high), and I use it for storage. There are some old lights in the crawl space whose circuits were routed in EMT, but I'd love it if code lets me run romex.
I don't see any reason you couldn't use NM B cable (aka romex).
 
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Old 09-29-13, 07:12 PM
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Granted, EMT will look all nice and clean, but it'll probably be covered up anyway.
Properly installed conduit always looks great, but not many DIYers can install conduit and make it look professionally installed. An obvious DIY botched attempt with conduit, in my opinion, lowers the value of the home. You have to think about these things if you may one day want to put your home on the market.
 
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Old 09-29-13, 09:53 PM
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#12 is limited to 20 amps by Article 240. The #6 is only good for 60 amps.
Ah ok I see. So even though #12 THHN is rated for 30A (from table 310.16), 240.4(D)--which applies to #14, #12, #10--comes into play and it stipulates that #12 must be protected by a 20A breaker.

But what about #6 THHN? Going by the same table 310.16, 90C #6 is rated for 75A. So assuming that no temperature adjustment is required, is there some other adjustment factor, similar to 240.4(D), that I'm missing?
 
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Old 09-29-13, 10:16 PM
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But what about #6 THHN? Going by the same table 310.16, 90C #6 is rated for 75A. So assuming that no temperature adjustment is required, is there some other adjustment factor, similar to 240.4(D), that I'm missing?
What you're missing isn't an adjustment factor. It's that the ampacity values listed at 90[SUP]o[/SUP]C. are only available if every component in the circuit is rated at 90[SUP]o[/SUP]C. The terminals and breakers you can buy readily and inexpensively aren't rated for temperatures that high.

You must use the values in the 60[SUP]o[/SUP]C. column for standard ampacities and conductor sizing. Joe said
I wouldn't protect the #6 any higher than 60 amps
because 6AWG copper is rated at 55A @ 60[SUP]o[/SUP]C. and you're allowed to go up to the next standard breaker size.
 
  #10  
Old 09-29-13, 10:40 PM
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I see. So derating doesn't actually hurt all that much because you never really get to use the 90C non-derated limits anyway. Got it. Thanks!
 
  #11  
Old 09-30-13, 04:00 AM
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The 90 degree column is where you start to derate from. The end number cannot be higher than the 60 or 75 degree column.
 
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Old 09-30-13, 02:53 PM
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you never really get to use the 90C non-derated limits anyway.
Sure you can. I've done it. But, as I said, every piece of the system was rated for 90[SUP]o[/SUP]C.

IOW, we didn't need to derate.
 
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