Sub panel to sub panel confusion.

ok here it is.

I have my main outdoor 200amp panel (its full) so I bought a 100amp sub panel which is mounted on the back of the same utility pole.
I have 3 gauge wire to run from a a 100amp breaker in my main box to feed the sub panel.

so I just bought and had placed a 12x24 shed about 60ft away from my utility pole that will be a in law suite and it already has a 125 amp service panel in it.

so from the 100 amp “sub panel” (connected directly from my main panel) to this new sub panel in the shed can I run 8/3 wire for 60ft to power the sub panel or is that not big enough gauge wire?

what will be running in the new shed:

1) small apartment size stove
2) small apartment size refrigerator
3) 1 12k btu window unit (9.19 amps)
4) 6 outlets (3 gfi)
5) 2 interior lights and one outside light

I put in a tankless water heater but that is being wired directly to the 100amp service panel next to my main panel on its own breaker so won’t be connected to the shed sub panel at all.

let me know before I hook this 8/3 wire up.

thanks in advance

 

#8 sounds a little light because that only gives you 40A. The water heater on it's own feed from the pole is not allowed. Only one feeder is allowed to serve power to an outbuilding.

 

The water heater will be hooked up into my 200amp panel not the 100amp service panel so because that water heater wire is fed into the same direction as the main feed for the shed, that’s not allowed?

 

Running two circuits to the shed is not allowed by the NEC. If the water heater is in the shed then it needs to get power from the subpanel that's in the shed.

 

Ok so if I include the water heater into the 100 amp service panel then with the other things mentioned that are in place with the 100amp be enough? If so then the feeder wire needs to be what 2 awg copper ran that 60ft?

 

A 100A feed to the shed should be enough, but with that said, what's the power demand for the tankless water heater? #3 Cu or #1 Al is enough for 100A.

 

220v 60amp 6/3 wire for the tankless water heater

 

The 100A may be enough, but you need to figure what the total load could be at one time with the water heater going plus what ever else may be turned on at the same time. Is a heater ever needed?

 

Well the stove calls for a 40amp breaker but no if a heater is ever used it will be a small space heater plugged in.

so the only thing that pulls high amps that could be running the same time as the water heater would be the stove which again is 40amp. I’m thinking I should get a 125amp sub panel to mount on the back side of the main panel cause the sheds sub panel is already 125amp but obviously was only ably to produce 100amp to it as of now.

 

Am I correct in assuming the 6-3 is UF-B cable? This is really a moot point since as has been mentioned, you are only allowed one power feed to a detached structure.



Again, is this UF-B cable?