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I have a subpanel almost wired in our shed, it's being converted into a tiny home for a few months, it's about 25ft from the main panel which is inside of a mobile home. The main panel I believe is 100 AMPS. The subpanel that is installed in the shed is 125AMP. It has 2 30amp breakers and 3 15 amp breakers installed. I need an opinion or 2 before proceeding.

Is it safe to wire the subpanel to the main panel? I don't think the sub will use even half of the capacity, so could I put a smaller breaker in the main?

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  • What loads are you putting in the shed, and what loads do you already have on the main panel?
    – ThreePhaseEel
    Commented Jul 25, 2016 at 11:45
  • In the shed there will be a 30 amp for a small Cooktop, 30amp for a under counter water heater, and then 15 Amp for 4 lights and 15 Amp for a few outlets. In the mobile home it's running 6 20AMP and a 40 AMP for lights, outlets, water heater, dryer, and Window AC.
    – Colton
    Commented Jul 25, 2016 at 11:48
  • You can always safely put on a breaker that trips earlier than required; that's extra safety. It might cause nuisance trips, but that's a convenience issue, not a safety issue. What you cannot safely do is put in a breaker that has higher ampacity than the maximum safe ampacity of the wire gauge.
    – Eric Lippert
    Commented Jul 25, 2016 at 16:07
  • Can you get me nameplate wattages on the cooktop, water heaters, window AC, and dryer, as well as square footages for both the mobile home and the shed?
    – ThreePhaseEel
    Commented Jul 25, 2016 at 22:17

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If you use a 100A breaker your main in the mobile home you will need #3 copper wire to feed the sub the sub panel. A 60 Amp breaker in the main panel should provide enough power from the loads listed this would require #6 copper wire.

You will need to run both hots a ground and neutral. In the sub the ground and neutral buses need to be isolated. Many times Panels come with the buses connected the connection will need to be removed or you can add a grounding buss screwed into the metal of the panel. (Make sure there is not a connection from the original buses to the box.)

I am hoping you will be living in the tiny house while remodel work is completed on the mobile. If both the mobile and the tiny house are used at the same time you may trip the main. If you trip the main you may have to do things like turn the AC off while the cook top is in use to prevent the main from tripping.

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