3HP 220 V motors - 20 amp or 30 amp circuits?

[Mike Williams]

My new shop is finally under construction , and the electrician should be showing up in about a week to start the wiring. I have a question on the wiring and circuit breaker size for 3 HP motors.

I will have individual 220V circuits for all of the heavier machines (air compressor, dust collector, lathe, tablesaw, bandsaw and planer). Each of these will be 3 HP motors.

None of the wiring runs will exceed 50 feet from the 200 amp sub-panel.

The best information I can find says I should size the circuit based on a 3 HP motor drawing 17 amps, and sizing the circuit for 125% of the load. That would mean each of these circuits should be sized for 21.2 amps. This means a 30 amp circuit and 10 gauge wiring.

Does that sound right? My gut feeling is a 20 amp circuit with 12 gauge wire would be ok. Are there any of the above machines that should definitely be on a 30 amp circuit?

Thanks, Mike

[Eddie Darby]

I would like to point out that there may be an advantage in having at least one circuit that will handle a heavier load, this way if you ever up-grade to a more powerful machine, you will be ready for it.

[Von Bickley]

The 3 HP cabinet saws that I have had experience with were wired with #12 wire on double 20 amp breakers.

Worked fine on these saws....

[Mike Cutler]

Mike.
I'm sure you'll recieve a lot of replies and opinions. In the end you'll install the breaker that the inspector wants to see there. I know that's a "crappy" answer, but there it is
The local licsense should know what the inspector wants to see.
A 20 amp breaker wit 12/2 will do it, but I'll be surprised if you don't end up running #10awg, and installing a 30 amp breaker.
The "heaviest loads" I see in your list is the dust collector, and the planer. A bandsaw resawing draws significant current also. They all have 3 hp motors, so I would expect them to all be treated equally.

[Robert Waddell]

After having two shops wired and two differ electricans, my answer would be #12 wire and 20amp breakers.
Rob

[Jim Fox]

My 3hp Cabinet Saw was run on a 30amp breaker in the old house, can't recall the wiring, think it was 10 gauge.

Just wired up the new shop and my electrician buddy told me 10 gauge. So, now the 3hp Cabinet Saw and ShopFox 1741 jointer are on 10 gauge runs, both 30 amp breakers.

[Luis Oliveira]

If my limited experience is any guidance, I have found that once you have 3HP machines you will soon start looking at 5HP machines, especially drum sanders, DC, and so on... so If it was me, will install at least 2 - 30A, 4-6 220 20A, and 6 120 20A. I will let more savy people tell you the gauge of the actual wire...

[Tom Veatch]

A 20 amp breaker is all you'd ever need for a 220v 3HP motor. It wouldn't hurt anything to run 30amp circuits if you so choose, but it's overkill. 12 ga 2 conductor with ground would be my choice for wire unless there's an extraordinalily long wire run from the box to the outlet.

Unless you're going to hardwire them as as a dedicated circuit, you'll run the wire to one (NEMA 6-20) or more wall outlets (NEMA 6-20 or NEMA 6-15) and the inspector would never see what's plugged into the outlet(s). And since these aren't continuous duty applications, the 125% upsizing isn't required.

I can't imagine requiring more than a 20 amp circuit to satisify a 3HP intermittent load (appx 12 - 15 FLA and much less than that on average). But, if you do decide to overkill it and go with 30 amp branch circuits, even for the 3HP machines, you'll need NEMA 6-30 outlets, and, in any case, a matching plug on the equipment.

I would suggest that you do use 30 amp/10 ga circuits for the Dust Collector and Air Compressor circuits. If you're going to upsize any of the things you mentioned to 5HP, my guess is those will be the ones. Unless you're looking toward becoming a serious production shop, 3HP woodworking machines are plenty big enough.

All the above, notwithstanding, my advice is to tell your electrician the intended use of the circuits and let him/her install what he/she knows is appropriate and will pass inspection.

[Rick Gifford]

My 3HP 220V motor is rated for 18 amps. So a 20 Amp breaker and 12 AWG wire is all that is needed.

[Gary Curtis]

My 5hp saw draws 19 amps. General of Canada told me when I bought it that the motor simply would not trip even a 20-amp circuit breaker. So, what does that tell you?

Gary Curtis

[Ken Fitzgerald]

Mike,

I ran 10 gauge wire and installed 30 amp breakers on all 8 of my 220 circuits. The difference in wire cost is negligible compared to the problems running it later. The breaker is really protecting the wire not the machine.
Thus if you run 12 gauge copper, use a 20 amp breaker.

Your electrician should know what will meet your local inspector's expectations.

[Steve Rowe]

When I built my shop, I wanted no electrical limitations for what I could potentially have in the future. There is no difference in cost between 20amp and 30 amp breakers. The only difference you would see is the relatively minor difference in cost between 10 gauge and 12 gauge wire. At the time of building the shop, 20 amp circuits would have satisfied my needs at the time. Now, 17 years later with several machine upgrades, I would have had to rewire my shop for larger circuits. Glad I went with 30 amp circuits.
Steve

[Tom Godley]

Here we go again!!

I am new to this forum and I very much like reading all the posts - many, have been a great help to me as I try to put my new shop together.

But, I must say that I have read too many posts regarding electrical issues that are not accurate - or better said not quite accurate.

From a safety "point of view" there is no direct problem with installing #10 or even #8 wire and then installing a breaker with a lower Amp rating -- say 20amp. We would not allow this in our factory on a rewire.

What some people do not understand is that 30A 240V is a lot of power- and it can kill you -- as well as allow a situation to develope that can very easily create a fire.

If a tool only requires a 20 amp line -- install a good 20amp breaker - you gain nothing having a 30 amp breaker on that tool.


sorry to preach

[Ken Fitzgerald]

Here we go again!!

I am new to this forum and I very much like reading all the posts - many, have been a great help to me as I try to put my new shop together.

But, I must say that I have read too many posts regarding electrical issues that are not accurate - or better said not quite accurate.

From a safety "point of view" there is no direct problem with installing #10 or even #8 wire and then installing a breaker with a lower Amp rating -- say 20amp. We would not allow this in our factory on a rewire.

What some people do not understand is that 30A 240V is a lot of power- and it can kill you -- as well as allow a situation to develope that can very easily create a fire.

If a tool only requires a 20 amp line -- install a good 20amp breaker - you gain nothing having a 30 amp breaker on that tool.


sorry to preach

Tom.......I've been working on x-ray equipment, MR scanners, Ct scanner for 31 years and I started working on radar and communications equipment used in air traffic control centersin 1970. Annually I have to take electrical safety courses via my company's EHS plan.

It's the current that kills you....milliamps are enough to kill you.......so 20 amps or 30 amps it really doesn't matter from a personal protection standpoint.

You can run 20 amp breakers and 10 gauge wire.......20 amp breakers and 12 gauge.......or you can buy one 30 amp breaker and use 10 gauge....the circuit breaker is there to protect the wire and prevent fire ....not protect you or the machine.

[M Toupin]

I must say that I have read too many posts regarding electrical issues that are not accurate - or better said not quite accurate.

Exactly...

What some people do not understand is that 30A 240V is a lot of power- and it can kill you -- as well as allow a situation to develope that can very easily create a fire.

Tom, with all due respect, 20A is just as dangerous as 30A and will kill you just as quick and just as dead under the proper circumstances. It really doesn't take much at all. At 110/220V, 50 or 60Hz AC can cause ventricular fibrillation at currents as low as 60mA. With DC power ventricular fibrillation can occur at 300 to 500 mA. So you see, weather it's 20A or 30A it's well over the threshold by a HUGE factor. 20A is no safer than 30A.

Mike, as far as circuits it sounds like 20A/12ga circuits would be fine for your present needs. You might want to consider any possibility that you might want to upgrade in the future though. Personally I would run 10ga if I was in your shoes, but that's just me. Most of us suffer from the Tim Taylor syndrome in that we like "more power!" and our machines keep getting bigger and more powerful. Another thing I haven't seen mentioned is you might also consider a 50A circuit if you think you might have a need for an arc welder in the future. I have a 50A circuit wired next to the door for just that purpose. That way I can drag the arc welder outside and not worry about a fire in the garage.

Mike