Running Electrical from House to External Building


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Old 03-14-18, 12:50 PM
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Running Electrical from House to External Building

Location : Nederland, TX.
I am wanting to come off of my 100-Amp Main Breaker from the Box Outside My House under the Meter to a Portable Building Behind my House. The Portable Building will be a home gym. Standard outlets, Lights, Window AC Unit, Cardio Equipment & Radio.

Its Approximately 125FT distance Between Main Switch and New Building Breaker Box. Which has 2-(20 Amp) Breakers installed with wiring to all outlets. And room for a few more (20-Amp) breakers.

I want to install a secondary switch or panel below main switch so that I don't have to shut off power to the house in the future when adding to the panel at the back building.
Should i Install a switch, or a Breaker. If So, what sizes.

Main 100-Amp Switch is inside Large Green Panel off of Meter. Panel to the right is for AC/Heat. 2-40-Amp Breakers.

What size/type Wire Do I need to run to the Breaker Box in the Outside Building. Im Assuming it is 2 wires, and a bare wire.
I am Running the Wire Underground, in Plastic Conduit, Approx. 10-12

Thanks In Advance!!
 
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Old 03-14-18, 01:01 PM
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First we would need to know the expected load at the outbuilding.

Unless you run a 120 volt 20 amp or less gfi protected circuit your depth will be at least 18 inches.
 
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Old 03-14-18, 01:13 PM
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You need to add a breaker in the main panel to feed the external building. I think most likely you'll need a 30A double pole breaker to feed the building which will require 4 conductors of #10 copper or #8 aluminum. As already said you need to figure up your total potential load to size the circuit. What size and type panel is in the external building? More than 6 breakers at the external building will require a main disconnect at the external building.
 
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Old 03-14-18, 01:40 PM
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The Expected Load in the outbuilding, currently it has 2 ( 20 Amp Breakers ) 6-Space Square D Panel, I don't see it needing any more than 3-4 breakers if that. Nothing Larger than cardio equipment plugs or a mini fridge.

Digging to 18" isn't a bad idea, but i was curious if it was unnecessary seeing as though it is insulated wire & within Conduit.
When you say #10 Copper, is this AWG-Size ? , also i googled a chart, and its recommending #4. but I'm thinking that is overkill since its underground.

Adding a Sub-Panel to the Main Switch would be ideal with room for breakers or future use..
Thank you for the input.
 
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Old 03-14-18, 02:02 PM
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You don't go by installed breakers to determine max load. You add up the amp usage of all the lights and equipment that may be on at one time. Be aware you need to use the proper wire for being in conduit that is outside and below ground. Nm-b is only allowed inside above ground in dry areas. What amperage is #4 being recommended? It's good for 85A. #10 is 30A and seems to be enough short of doing load calculation.
 
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Old 03-14-18, 02:25 PM
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Ok, that makes sense,
here is what i came up with for amperage

Lights / Radio / Fridge / TV - 4-5 Amps max
Stairmaster - 15-20 Amp Dedicated outlet
Treadmill - 15-20 Amp Dedicated outlet

Cardio equipment is likely to not run at the same time.

# 4 wire shows to be, 30AMP at 130FT Long.

Thanks again
 
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Old 03-14-18, 02:50 PM
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You need the actual amp usage of the equipment not the suggested circuit size to figure load. That being said I believe a 30 amp 240/120V feed to the building is enough. I don't know where you are looking and coming up with #4 for 30A because that is not correct. #10 AWG copper is fine for a 30A feeder at 130ft for the loads you will have. The most you would need is #8 AWG copper if pushing the load to a full 30A.

What about the window A/C?
 
 

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