What size breaker box/amps do you think I'll need for my new pole barn gymnasium?

Question

I have 200 amp service at my house and running electric 200 ft to a 50 by 80 pole barn with 60 by 50 basketball court. So my electric needs will be

• Several warehouse high bay lights

• wood furnace blower

• pump for water cistern

• Lights in finished 20 by 50 area that has an office and some fitness equip, rowing machine, treadmill.

• Electric water heater 30 amp

• TV, surround sound

• Probably 15 amp heater for extra heat occasionally in office

• no garage door openers

Any advice help appreciated!!

Answer 1

Spaces are cheap. Buy a 30-40+ space 200A panel and don't have the regret later on of not having spent small change on the difference between that and the smallest panel for the number of breakers you could think of when you installed it.

Good practice and/or up-to-date code (the former always applies, the latter depends on what code is adopted in your area) will eat two spaces on a surge suppressor, for one additional thing you didn't think of. You also have required lighting and receptacle values based on square footage, not on what you thought of powering.

Your 15A will go a lot further feeding a cold-climate heat pump than a resistance heater.

Answer 2

A bunch of little, but possibly important, things:

• Panel Size - You will need a big panel. Don't count on 1/2-size breakers - plan on completing this entire project with full-size breakers and several spaces left over. That way 10 years from now you might be able to make use of 1/2-size breakers if absolutely needed. If you use them now (which saves very little) then you are really stuck if you need more spaces later.
• Main Breaker Size - Big panels often come with a main breaker and a bunch of branch circuit breakers. You will need a shutoff because this is a separate building, so that main breaker can be the shutoff. It does not need to match the feed - e.g., if your feed is 100A, the breaker in the main panel at the other end of the feed needs to be 100A but the breaker in the subpanel can be any size 100A or larger - e.g., the 200A breaker bundled with the panel.
• AFCI and GFCI - A lot depends on the jurisdiction, version of NEC and type of building. But you will, at a minimum, need GFCI in kitchen (within 6' of sink) and bathroom and any other wet areas. You may need GFCI everywhere based on this being treated as an outbuilding. Or you may need AFCI almost everywhere based on this being a regular building. Hard to guess without more details. But keep in mind that AFCI is generally best at the panel (AFCI/breaker) while GFCI can be at the panel (GFCI/breaker) or at the receptacle (GFCI/receptacle) and is often both more convenient and cheaper at the receptacle. Multiple receptacles can be chained off a single GFCI but need to be labeled (per code and, particularly in a big space, for practical reasons).
• You essentially have a small residential space (office/kitchen/bathroom) and a large industrial space (gym). Assuming the residential space has low ceilings and typical requirements, you may want full HVAC there, and a heat pump makes sense. For the gym area, you need to think carefully about HVAC. For a space that size with high ceilings (can't play basketball very well with 8' ceilings) HVAC can get a bit pricey. Depends on local weather, insulation and planned use summer vs. winter.
• You will also have to meet all the typical requirements for kitchen and bathroom in terms of required circuits. You may be able to get away with the kitchen not being a kitchen if it is just sink + refrigerator + microwave with no oven or cooktop. But from a practical standpoint it makes little difference, as 1 of the two countertop circuits can be used for the microwave (unless it is a built-in, but those cost a lot more) and then 1 for other stuff, and the GFCI requirement is there because of the sink, whether or not it is a true kitchen.
• In a house, and likely in your office area, you need to have a receptacle every 12' along the walls. That may or may not apply in the gym. You can have several receptacles on each circuit, but multiple circuits is definitely a good idea - e.g., at least 2 in the office, and in the gym at least "number of exercise machines that use power/2" + 2. As you can see, you're going to need a lot of breaker spaces.
• Use metal conduit in the gym. It provides the ground, makes reconfiguration easier (e.g., if you add another machine and it needs a dedicated circuit) and provides protection from damage. Assuming the office has regular walls (e.g., drywall), protection is not an issue there.
• Lighting - At least one lighting circuit in the office. I recommend at least two lighting circuits in the gym. One 20A circuit could probably handle everything with LEDs, but having two circuits allows you to work on one (e.g., replace a fixture) without the whole gym going dark. Do not put lighting on GFCI unless required by local code (which is usually not the case).
• Feed Type - Definitely use aluminum wire for the feeder. Highly recommend large conduit as (a) you don't have to bury it as deep as cable and (b) you can (if the conduit is large enough) replace the feeder in the future much easier than with cable because you won't have to dig again.

Answer 3

You need to do a Load Calculation on the building.

This means tallying up all your hardwired loads and 240V loads. You are looking for "VA" on the nameplate of the appliance. If you can't find VA, look for Amps and multiply by the voltage (120 or 240, there is no more 110V anymore). That will give you VA (Volt-Amps).

VA is not quite the same as watts. You need to use VA.

On the large appliances, take any appliances that will never run at the same time (furnace and air conditioner) and cross off the smaller one, it won't count.

Now for lighting loads, determine that VA and add that in too.

For receptacles, figure 180 VA per receptacle yoke. 220.14(I). For each kitchenette circuit override that so there is at least 1500 VA on that circuit.

Now that you have a total VA, divide by 240 and that's the minimum amps you'll need.

Give that about a 30% boost to allow for the long distance of wire. Now you can size your wire for that.

However "smallest is cheapest" does not apply to wire. Due to the economics of wire, your best options go 20A -> 90A --> 100A -> 120A. That is because at 90A, most people cross over to aluminum wire, which is perfectly fine/safe at these large sizes. 90A is unusually cheap, because it's extremely popular (being the wire of choice for 100A services).

I have a feeling the above calculation will get you to somewhere between 30A and 90A, so the 90A wire is the natural choice. This is #2 aluminum.