How to tell if a motor is 3-Phase

[crazyal]

You guys do know you can use caps to start the motor spinning, right? I'm a little rusty on my electrical skills so it would be better to use google but a few caps (depending on the motor size) and you'll never be trying to spin start the motor.

 

[Inspector507]

But as this reads 115 / 230 my gut is telling me this is 3 phase. If not, how can a motor run on 115 or 230?

If I read a nameplate that says that, my gut would tell me it is "probably" single phase.

 

[magicheater]

But as this reads 115 / 230 my gut is telling me this is 3 phase. If not, how can a motor run on 115 or 230?Carl

115 volt is single phase, 230 volt is 2 phase. Either leg to neutral is single phase and 115 volts. The difference is how you connect the windings in the motor. All normal residential entrances are 230 volts. You can run a 115/230 volt motor either way by changing how you connect the windings. You can run a 3 phase motor on 2 phase by inducing a voltage in the third leg of the 3 phase motor. The main difference is the efficiency, I.E. less amps for a given amount of work done. 115 volts can be had in a 230 volt 3 phase panel by connecting one leg to neutral. However you must be careful as some 230 volt entrances have what is called a wild leg and you end up getting 160 volts or so if you connect that leg to neutral. This is all determined by what sort of transformer setup the power company uses. Hope all this was helpful.

 

[ultrarunner]

You guys do know you can use caps to start the motor spinning, right? I'm a little rusty on my electrical skills so it would be better to use google but a few caps (depending on the motor size) and you'll never be trying to spin start the motor.

The price was right and it's worked well for almost 30 years for the Bridgeport. All I needed was to splice in 3 wires from the mill and a short length of rope to "spin" start my 1 hp converter.

Another retired machinist friend had a complete shop at his home... it all ran from one 5 hp rotary converter... mill, lathe, grinder and air compressor.

He built a little device with an over-riding clutch using a small 117 volt motor to "Start" the 5 hp converter... it took less than 10 seconds for 3-phase to be on-line.