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I installed a hot tub and ran the 60 amp line for it from a 100 amp sub panel. The sub panel is full and the inspector said he wouldn't allow it because there are too many big draw circuits in it. He said it may be ok if there's something in section 220.14 ( additional loads ) that can help. I'm not sure after reading it that there is. I turned everything in the panel on and each phase only reads 38 amps on my amprobe. The main 200 amp panel is also full and pretty hard to get to. Not sure what to do.

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    A picture of your subpanel showing the breakers would be helpful. Details on what the breakers supply may also help.
    – blarg
    Commented Feb 27, 2022 at 15:18
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    Can you post photos of the subpanel in question please? Commented Feb 27, 2022 at 16:49
  • What's the actual load of the hot tub? ... Not breaker size but add up total amperage.
    – JACK
    Commented Feb 27, 2022 at 20:18

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Ever have a checkbook with paper checks? You know there's a difference between "how many checks you have left" and "how much money is left in the account to spend". In fact, one has nothing to do with the other!

The same exact thing applies to "number of breaker spaces available" (checks) vs "power required by the loads" (money). "The panel is full" is the obvious barrier directly in front of you. But it has nothing to do with the ampacity question, and I think that's what the inspector was concerned with.

The thing you're looking for is a Load Calculation.

There's a gold-standard way to do a Load Calculation for a dwelling. It's a little too complicated to describe here, but it is based on the nameplate data off certain large appliances (some of which go through a calculation in your favor, such as a range), a 1500W allocation for kitchen and laundry circuits, and a "3 W per square foot of your house" catch-all that sweeps in all general-use loads (so you don't have to think about refrigerator, blender, TV, computer, hair dryer etc.)... with some additional (favorable) derate then applied.

The Load Calculation needs to be done a) for the whole house and the service; and b) for the subpanel to assure it is not overloaded. It should be done without the hot tub, and re-calculated again with the hot tub (i.e. re-work the whole thing, don't just add the hot tub's ampacity because that would short-circuit a favorable derate).

If the subpanel is overloaded and the main isn't - and the subpanel is less than 125A - then this can be corrected by enlarging the feeder to the subpanel. Since the sub is out of spaces this is also a great time for a larger subpanel.

By the way, this situation is why we implore people to use a fantastically large subpanel. The last guy chintzed out, and got a what, 6-space? 12-space? subpanel from thinking "that's big enough for my immediate needs. I could buy bigger, or I could buy a pizza. I like pizza." I say the opposite: Spaces are cheap. Go wildly oversize on the panel so you never have to do this again.

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