correct breaker for 230v

[snipe]

As this is my first post, I would like to thank all you for informing me on all aspects of my new found interest in ww.
My question is "what is the correct size breaker for a 230v line. My compressor runs a 5 hp. 22.0 amp. and I will be replaving my ts motor with a 2 hp. 220-230v.
I have had two people give me two different answers. One was for a 40 amp. the other one was for a 20-25 amp. It will be a new line and the 20-25 amp friend said that the first guy was calculation the 40 amp. based on a 110 line.
Can anyone with the correct kowlege give me the right answer, I dont want to burn the house down lol. Thanks again for all your input.

[Ken in Dartmouth]

FWIW A 30 amp breaker will let you run a motor up to about 8 hp. If you look at your distribution panel, you will see that all 220-volt breakers are 30 amp, with the exception of the range supply, which is 40 amp. Does this help?
Ken in Dartmouth

[Doug in Little Spain (Pr.]

Non-electrician here but I have a concern with running your table saw on that 30 amp line unless there is some overload protection at the saw, e.g., magnetic starter.

Generally, the rule is to multiply motor loads by 1.25 to determine the breaker size, the cable size, and the outlet size. So for your compressor, you are right on with the 30 amp breaker.

It sounds like you have a real 5HP compressor that actually draws what a real 5HP motor should draw. My "6 HP" compressor runs on a 15 amp 220 volt line as recommended by the manufacturer. The plate on my compressor does not list an amperage for the motor.

If you also have a nominal 5HP compressor, you may be able to run it on a smaller breaker (check the manual), and your problem will be solved because one breaker will be able to handle both machines but not at the same time.

Here's the problem with a 22 amp compressor and a 2HP table saw. Chances are the saw could and should run on a 15 amp 220 volt line because it's a lot lower load than the compressor. If you run it on a bigger breaker, there is no protection for the motor. In general, motors are not supposed to be protected by the line breaker; they are supposed to have their own protection, but do you?

So what's your setup? Do you have just one cable to run both machines? Is it #10 wire?

By the way, you are wise in checking out how to hook up these tools properly.

[Bill Howatt]

You are right about the motor (and anything else other than the building wiring, for that matter) not being protected by the breaker. Ideally all motors should have overload protection but as you imply not all of them may.

I don't think my 2HP TS motor has such protection but I also don't get too excited about it since it is always run in attended operation. If it doesn't start, stalls, seriously bogs down I am there to turn it off. This is typically not the case in industrial settings or even your washing machine.

Bill

[snipe]

Thanks for all your input. I intend to run at least # 10 wire if not # 8. The line will be for both all be it one at a time. The TS start switch is a industrial switch with protection, but it is for up to 3hp which I was told was a bit to high for a two hp. I guess I will run with this switch for now and look into a more suitible one when the budget allows.

[Michael in Port Alberni]

Hopefully this will clear a few things up...

Look at the fla of the motor. Full Load Amps. Breakers are designed to tripp at 80% of their rating when that 80% is exceeded on overload for more than 2 minutes. They are designed to trip instantly on short circuit... two very distinct faults. 30a=24a, 15a=12a, 40a=32a etc. Most motors have overload protection built in by the manufacturer, those little black and read buttons on motors that will pop whhen the windings heat up. Putting two motor driven machines on one cct is not the best strategy, especially if you are running new wire anyway.

My next article in the magazine will go into this in a little more detail....if you have any specific questions.. just post em or email me.

Cheers

Michael Kampen

[Mike Harris, London]

Hi Snipe

Where is your shop.

If it's in the basement, run #10/3 and a 30A 2 pole breaker for your compressor and #14/2 on a 15A 2 pole breaker for your TS. Do not run your TS on the same 30A breaker as your compressor.

If your shop is in your garage or a separate building install a Sub or Pony Panel in that location, fed with #6/3 and a 60A 2 pole breaker in the main panel. Then size your wire and breakers the same as above, your whole shop could then be run off that panel.

More expensive, yes, but it's the right way to do it. I recomend taking a permit out as well. Wouldn't want to give your insurance company an out would you?

Mike

[Bill Howatt]

Where do you get the "breakers are designed to trip at 80% of their rating ..."?

My interpretation of Square-D breaker curves indicate a minimum trip time of about 350seconds at 100% rating and never tripping at 80% rating within the 2.75hrs shown on the graph. This is with a 40C ambient temperature. They are much longer at 25C ambient. The curve actually shows that breakers may go much longer than 350 seconds at full rated power without tripping.

Bill

[Danny in Nova Scotia]

Snipe
Mike is right. That is the proper way to do it. It may cost a little more, but isn't the peace of mind worth it?
Danny