I have a 200 amp service panel, and I calculate I am using about 160 amps. (I used a formula I found online that takes the square footage of the house and then adds from there) The new 160 sqft shed is on the other side of the breaker box so the run will be about 80 - 90 feet. In the shed I want to run a mini split air/heat that requires a 240v 15 amp breaker. I would also like to have a 120v 15 amp breaker for lights and a 120v 20 amp breaker for plugs. Lights will be led fluorescents and the plugs will be light duty tools and battery chargers so not really very much draw at all. The shed will be insulated and sheetrocked. It is 10 feet at the peak of the roof. The mini-split is 27.5 seer and 550 Watts so should draw too much either.
I have space in my service panel to add a 240v breaker, two poles, 25 amps and 25 amps and I will run 2 hots, 1 neutral and one ground number 8 AWG THWN2 through 1" pvc at the service panel into the attic where I would switch to Carlon flexible Blue conduit, then pop out the other side of the house and go back to 1" pvc down the house and 18" into ground to the shed. I was thinking at that point I would run it to a 60 amp disconnect switch and then through the shed wall to a indoor subpanel maybe 100 amps with my three breakers. I read that the sub panel would need the ground and neutral unbonded and that I would need to use 2 8ft grounding rods 6 feet apart so will do that.
So does that sound reasonable?
If the new 240V 25 amp double pole breakers add up to 50 amps, that would technically give me 210 amps usage at the service panel. 160 + 50. Would that be okay on a 200 amp service? Or is it counted as only 25 amps in which case I would be fine.
Also, at the shed's sub panel, I would have those 3 breakers adding up to either 65 amps if the 240 15 amp gets added as 30, or else it would be 50 amps. Would the 240V double 25 amp breaker be big enough to support the 3 breakers in the shed? Is number 8 wire big enough or do I need to go to 6 awg?
The 60 amp disconnect has two line and two load connectors and a ground. However there is no place for the neutral. Would I just pass the neutral through the wall into the subpanel and not be involved at all with the disconnect wires? I'm thinking the disconnect just needs to break the hots and not the neutral, but wanted to make sure.
Thanks for any help. I'm relatively new to electrical wiring so want to be sure I'm doing it all correctly and up to NEC standards.