100 Amp Subpanel

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  #1  
Old 01-09-14, 06:49 PM
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100 Amp Subpanel

I am going to wire a 100 Amp sub panel in our garage for two NEMA 14-50 outlets for electric car charging. Each outlet could be running simultaneously at 40 amps each for several hours at a time. The run from our 400 Amp main panel is about 50' and will run under the house in a crawl space. I am thinking about 3 options:
1) 1.23" or 1.5" PVC conduit with 3 2g THWN wires and a ground (not looking forward to the complex conduit path
2) using 1.25 or 1.5 liquidtight conduit (guess I need type B?) with same wires, not sure if this is OK to use for such a long length.
3) Or a service type of line with either 1-1-1-3 copper or 1/0 aluminum. (this stuff seems hard to find)

Any suggestions?
Thanks
 
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  #2  
Old 01-09-14, 07:46 PM
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Welcome to the forums!

Is 40 amps the actual load or is that the size breaker you would need?

Option 1: You would need 4 wires in PVC conduit. 3 x #3 copper THHN for hot, hot and neutral and one #8 for the ground.

Option 2: You would also need 4 wires of the same size as option 1. It would be OK for the length, however at that size, it will be very expensive.

Option 3: A cable must be approved for inside a house. You need something like NM-b (romex). #2 copper would ok for 100 amps, or 1/0 aluminum.
 
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Old 01-09-14, 08:21 PM
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for two NEMA 14-50 outlets for electric car
Are you sure you need 120/240 and not just 240? Sure it isn't 6-50. Seems odd a charger would need dual voltage but then I know nothing about the car chargers.
 
  #4  
Old 01-09-14, 09:20 PM
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Thanks for the replays. Subpanel would have two 50 amp breakers, each drawing 40 amps continuous. Yes, outlets would only need 240 and a 6-50 outlet would work fine. Was planning on using 14-50's as this is the standard adapter that comes with the car (Tesla). Probably would be cheaper to buy the 6-50 adapters and then would only need to run 6/2 to each outlet.

So for 100 amps, #3 in conduit or #2 romex type cable would be OK? Somehow thought I would need one size higher.

Thanks.
 
  #5  
Old 01-09-14, 09:34 PM
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Why I asked if 240 only: If the garage is attached you can install a 240 only panel that saves you the cost of running a neutral wire. Only two hots and a ground or 2-2 NM-b. If an attached garage you can leave in place any 120 wiring in the garage because the panel needs only to supply the receptacles.
 
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Old 01-10-14, 12:15 AM
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I would just run two 6-2 cables, one to each charger. Much easier to deal with than conduit. You could sleeve the cable if necessary where exposed.
 
  #7  
Old 01-11-14, 02:10 PM
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Thanks for all the advice. On further reading it seems 2/3 NM-B is good for 95 amps which is OK to use with a 100 amp breaker. This seems the easiest. I think you are right, I will just run 6/2 to each of the outlets and get 6-50 adapters for the chargers (35$).
The 2/3 should be much easier to run than trying conduit.
The other option I considered was flexible metal conduit with #3 but I don't think this is code to use in a crawl space.

Thanks again.
 
  #8  
Old 01-11-14, 02:43 PM
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it seems 2/3 NM-B is good for 95 amps which is OK to use with a 100 amp breaker.
Actually I believe PCBoss meant no subpanel. He meant run two 6-2 NM-b from the main panel.
 
  #9  
Old 01-11-14, 03:21 PM
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Thanks for the clarification. I am planning on getting a separate meter to get EV rates so want to keep them both on the same circuit.
 
  #10  
Old 01-11-14, 03:52 PM
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Originally you wrote:
The run from our 400 Amp main panel is about 50' and will run under the house in a crawl space.
Now you write:
I am planning on getting a separate meter to get EV rates
Is the subpanel going to have a meter that will subtract from the main panel meter? If you run from that existing panel then any electric will be metered by that panel.

However if the charger receptacles will simply have a meter that bills you for amount used it will have to have its own meter and panel.
 
  #11  
Old 01-12-14, 11:01 AM
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I looks like they run from main meter, thru 100 amp breaker, then to second meter, then to sub panel. The use of second meter is subtracted from the main meter. The off peak EV rate is .06$ versus my tier two .18$ rate.

I think I have it figured out. I am planning on running 2/3 NM-b thru a 100 amp breaker to the sub panel, then two 6/2 runs with 50 amp breakers to the 6-50 outlets. Let me know if there is any problem with that plan, otherwise, thanks to everyone for the help.
 
  #12  
Old 01-12-14, 12:00 PM
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You will have to group the services.
 
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Old 01-12-14, 05:25 PM
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I looks like they run from main meter, thru 100 amp breaker, then to second meter, then to sub panel. The use of second meter is subtracted from the main meter.
I'd advise you to call your power company and get a cut sheet with the specifications and requirements for this second meter installation.
 
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