4 commercial tread mills, call for 20 amps each The distance from the source to the proposed wall outlets will be at least 100 ft. Need to know the size of the wire required. Iwill have a certified electrician do the work. I am in S.C.
Thanks, Wallace

If you are hiring a certified electrician, they will know what to get. Considering they are 20 Amp each and may be running at the same time, you will need 4 circuits. I would have them install a subpanel rated for 100 Amps and then run wire to each of the treadmills.

If they are rated at a full 20 amps, the minimum breaker for continuous loads has to be rated at 125% or in other words each circuit needs to be rated for 25 amps. If the treadmills call for a 20 amp circuit breaker, but draw only 80% or less of that 20 amps, then the 20 amp breaker will work.(16 amps continuous load or less). You have to clarify this to get the proper rating. Normally #12 THHN wire will be sufficient for 20 amp circuit breaker if you are actually running 16 amps. If you run the #12 THHN all in one conduit then there are de-rating factors on top of the continuous duty de-rate for more than 3 conductors in a raceway. If you run all the way 100' for each circuit, I would suggest #10 THHN wire for the circuits. If you run a sub panel instead, you will have to figure the continuous load at 125% of the largest load and 100% of the rest for the sub panel. Example: 4 loads at 16 amps you would figure 1@ 125% load or 20 amps and add the other 3 at 100% load or 48 amps plus 20 amps = 68 amps minimum for sub panel. Next size circuit breaker is 70 amps, so sub-panel would be no less than 70 amps given 16 amp load on 4 circuits.
If the actual load is 20 amps, then 125% of 20 amps = 25 amps, plus 3 * 20 amps = 60 amps. 60 amps + 25 amps = 88 amps minimum sub panel for this case. Next size circuit breaker is 90 amps. The post before this suggested 100 amps for a sub panel, which should easily handle your load and maybe give you some additional space for another treadmill or some other equipment. You have to make sure the panel that is supplying this, or these loads is not already overloaded. A load calculation can be performed by a qualified electrician.

A good rule of thumb I use for an existing load calculation is to run the normal loads that you run and check with an ammeter to see the current draw on the existing panel. If you are careful to include(turn on) all the things that are in normal operation, this will put you in proximity of how much load is currently used by the supplying panel and how much is available to you for your treadmills or treadmill sub panel. It may be that you will have to go to a larger service panel or alternate loads to accommodate your situation. Often a manufacturer will specify a 20 amp circuit breaker for a piece of equipment, but the actual load is somewhere 16 amps or below. If the device says full load current = 20 amps, then a minimum of 25 amp breaker and 10 gauge wire will be needed for the outlets. I might say that 20 amps on a treadmill sounds a little off the charts to me as far as actual current draw. It might need a 20 amp breaker to handle the starting current and then settle down to a modest amperage. Most treadmills I know have a ramped start, so this is not likely on a treadmill. My educated guess is that each treadmill is running 16 amps or less, but I have been wrong before. There may be other factors that need to be considered by your electrician and the way he approaches the problem. Your business may be such that not all of your machines are ever running at the same time which gives you some latitude if things are borderline. You will know more about the usage of the total system than can be thoughtfully discussed in this forum.

FYI one of the reasons for the 125% factor for continuous loads is that the breaker will build heat overtime and trip due to thermal load on the breaker. A 20 amp breaker will trip at 20 amps on a short circuit almost immediately. If the circuit runs at near 20 amps for a significant time it may nuisance trip due to heat build up in the breaker and that is why the code only allows 16 amps (80%)as a loading factor for the 20 amp breaker. (same is true for other breaker sizes)

Good luck with your project. Probably more information than you wanted, but you can trash what you don't need. I would appreciate it if you would run on the treadmill 30 minutes a day for me, then I could get my DR. off my back.