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Do I need a 3 phase breaker after my phase converter or can I just use the single phase breaker?

DavidScott

Titanium
Joined
Jul 11, 2012
Location
Washington
If using a 10hp Phase Perfect to power a CNC mill that wants a 30 amp service do I need the 30 amp 3 phase breaker after the phase converter or can I just use the single phase breaker feeding the phase converter, if sized correctly? This is the only machine wired to the phase converter.
 
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Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
Single phase breaker should be fine. The machine has a breaker built into it.

If the phase converter was feeding multiple machines then I'd suggest a fused disconnect for each machine.
 

DavidScott

Titanium
Joined
Jul 11, 2012
Location
Washington
I buck the single phase voltage to 200 before the phase converter. Is the formula 30 amps 3 phase x 1.8 = 54 amp single phase breaker? The Phase Perfect only uses 180 watts.

I have been running my cnc mills this way with a 60 amp single phase breaker fine since 2004.
 

DavidScott

Titanium
Joined
Jul 11, 2012
Location
Washington
For what it is worth the installation manual for mine states that I am to supply power through a 30 amp breaker so it doesn't sound like mine has one. But it should be here tomorrow morning so I will soon know for sure.
 

tmt

Hot Rolled
Joined
Apr 5, 2005
Location
Southwest
Single phase breaker should be fine. The machine has a breaker built into it.

If the phase converter was feeding multiple machines then I'd suggest a fused disconnect for each machine.
I believe that is a option, the best I remember. It also has a disconnect handle on the outside that meets the disconnect requirements for the 3 phase breaker panel it supplies. When pricing just a disconnect switch large enough for the breaker panel it was more than the one on the Phase Perfect.

Besides it would have been just another huge box that needed to be mounted on the outside wall plus having to pay the electrician to hook it up.
 

tmt

Hot Rolled
Joined
Apr 5, 2005
Location
Southwest
If the nec is important, you need breakers on the in and the out...Phil
I have a main breaker in the panel as well. My electrician insisted that I have Interrupt Rating of 22kA vs 10kA on the breakers. He was always long winded on his explanations and most of it went over my head. He said you couldn't mix 10kA breakers with 22kA breakers, something about the weakest link or something to that effect as I grumbled about the difference in price. I never won a argument with him and that is alright with me since IMO he did a bang up job.

The only time I was able to get his goat was when the dry wall guys covered up a couple of his outlets. He pissed and moan for an hour about it. As I was leaving I turned and said, "your measured each outlet position at least three frigging times and you can't remember where the hell you put them!!" then I rushed out the door.
 

BT Fabrication

Hot Rolled
Joined
Nov 3, 2019
If using a 10hp Phase Perfect to power a CNC mill that wants a 30 amp service do I need the 30 amp 3 phase breaker after the phase converter or can I just use the single phase breaker feeding the phase converter, if sized correctly? This is the only machine wired to the phase converter.
Id suggest putting a pull throw disconnect that is fused on each side.
 

nt1953

Hot Rolled
Joined
Sep 4, 2004
Location
Huntsville, Alabama
If I am correct on how motor starters work, and if your motor starter on the powered equipment has what are sometimes called heaters, and they are sized correctly, they should provide all the protection you need.
 

rons

Diamond
Joined
Mar 5, 2009
Location
California, USA
The only time I was able to get his goat was when the dry wall guys covered up a couple of his outlets. He pissed and moan for an hour about it. As I was leaving I turned and said, "your measured each outlet position at least three frigging times and you can't remember where the hell you put them!!" then I rushed out the door.
Buy the guy a neodymium magnet for his birthday. Tie a string to it and just walk up and down the great wall of ....
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
If I am correct on how motor starters work, and if your motor starter on the powered equipment has what are sometimes called heaters, and they are sized correctly, they should provide all the protection you need.
Please explain what CNC has a motor starter in it's primary wiring.
 

Vancbiker

Diamond
Joined
Jan 5, 2014
Location
Vancouver, WA. USA
Please explain what CNC has a motor starter in it's primary wiring.
Some folks call the contactors for motors on the hydraulics or coolant or other peripheral devices, starters. Typically those have an attached or integral thermal overload.

In any case, the reference to them by poster nt1953 is totally irrelevant to this thread as those loads are minimal in almost all CNC machines.

 








 
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