Thread: Is there any reason you cannot use single phase breakers as three phase?

Is there any reason a guy cannot use two 220v single phase breakers to connect a three phase line? (just leave one pole empty) if you can, would the rating stay the same, or do you have to multiply or divide the indicated capacity by the 'magic' 1.732?

I'm supposed to have a 120 amp breaker on this new machine, and QO doesn't even make 120 amp three phase breakers... (according to their website) but they DO make single-phase ones...

Thanks!

IT is unsafe because if one breaker trips the other phases could still be energized unless there is a bar mechanically attached to all three switches. So if one phase trips, they all go off.
Otherwise they are the same. You could use a two pole breaker and a single.

As lectrician1 said. If you get three identical single-phase breakers and use a recognized (means has UL mark on it and was designed for the purpose) tie bar to bind all three breakers together so they all go off when any one of them trips, then you're OK. Otherwise it is neither safe nor legal. And you certainly can't use just two breakers for a three-phase machine.

I have seen electritians use 3 single pole breakers on a 3 phase panel. They take a piece of 1/8" welding rod and run it through the "arms" of them all-jsut like a 220 breaker uses a little plastic clip to do it for home use. I understand what you are doing with the 2 220 breakers-same thing-but take the connector off of the arms of the second one and make sure the three are linked together. The unused arm can be used for a 110 curcuit.
Joe

A followup: the phrase "two 220v single phase breakers" in the original post can be misleading. "Single-phase breaker" usually implies one-pole. US household 220V circuits require two-pole breakers. To protect a three-phase circuit, you must use three poles. NEC Article 240.15(B)(3) says if you are protecting 3-phase circuits with multiple single-pole breakers, you must use an identified handle tie. (I said "recognized" above, but the actual Code language is "identified".) In other words, improvising a handle tie with welding rod does not comply with the NEC. As a practical matter, you need to select single-pole breakers designed by the manufacturer to be tied.

If Square D is the brand, I recall tie handles being offered.

http://static.schneider-electric.us/...040-080-06.pdf

http://www.schneider-electric.us/sup...en&id=FA125159

http://www.schneider-electric.us/sit...&redirect=true

http://products.schneider-electric.u...rtNumber=QO3HT

Do we make a handle tie for three single pole QO and QOB breakers?
Yes, use a QO3HT. Note the handle tie does not give common trip to the three poles.

We don't know the exact layout of your electrical service, so we can't provide all your possible options.

I know what you mean too. Every time I hook up a machine it costs me 200 - 250 bucks for a 3 pole breaker.
I thought of hooking a couple of my machines up with one two pole breaker and one one pole breaker but to get the 3 phases the machine needs.
I have tons of them kicking around.
It might work initially but if one trips and the other doesnt for whatever reason it might cause issues. No to mention the potential hazard of someone getting fried because I was too cheap to buy the proper materials.
I try to save a $ where I can but when it comes to electrical I'd rather it be done once and properly so I dont have to worry about it in the future.
As for the cable going to the machine, I will throw BX armoured cable up before conduit & pulling wire Any day because:

a) It's cheaper
b) It's code / allowed
c)The machine works just the same as any other connection (as long as you have the right gauge)

h.s.

Most of the 3-phase breakers I've worked with were single-phase segments... Aside from tying the handles together, a manufactured 3-phase breaker has skinny little bolts that pass through two holes in the body, so it's all one rigid unit... and I have made three-phase breakers out of singles not only by tying the handles, but also the bodies.

Most good-quality industrial-grade breakers are made with this specifically in mind... furthermore, there's requirements in NEC that if you have multiple circuits sharing a neutral, or some other conditions, that the breakers must be tied together to protect against a variety of weird, but bad things happening.

So the answer is yes... and if the breakers you have aren't industrial-grade enough to have such hardware available, I highly recommend you replace them with industrial grade AND use the kit, as the result is much better than cobbling- the breakers won't bind and jam, and they'll fit in the panel properly.

I have been staying out of this because I figured it would be resolved. NO you cannot use single phase breakers for three phase and be certain of proper functioning. If one trips with the handles tied together, it probably will pull the other two off, but "probably" doesn't fly here. If you disassemble a three phase breaker, you will find that the segments that look like separate units are actually tied together internally with a bar that trips the other two if one goes. Tying the handles makes them switch on and off together, eliminating the possibility of getting one circuit hot, but the three phase trip is not done by the handles. I have one apart at the shop right now because a machine cleaner sprayed cleaner in a breaker. Fire shot out of it and the machine would not run. Fortunately, he did shut it off first, so the VFD was not damaged. I had an old one at the shop, but one phase didn't close. I had no luck fixing it, so I wound up paying Grainger $257 for a new one, which didn't make my customer turn cartwheels of joy, but I got his production running. If you want, I will post some pictures.

Bill