3 phase switch question

[chip hayden]

i'm wiring the slotter on one of my Bridgeport milling machines and the on/off toggle switch was removed by someone. the box and cover plate are there but the switch isn't. it's a 1/3 hp 3 phase motor. and the switch cover has the standard @ 3/8 dia. hole for the toggle.
do i need a three pole single throw switch for this motor? thanks guys.

[lranch]

Switch

This sounds like low volt 3 phase? If the switch has been designed to control motor leads, yes. However, it's never a good idea to require operator to manipulate line volts. A seperate contactor and control transformer (smaller, lighter, more mounting options, SAFER, etc) should be used. As I'm not on site, the only other thing I could mention is all 3 power leads must be controled on any 3 phase device, i.e. for on-off, direction. What you most likely have is a switch/starter combo. Call the lectric guys and tell them motor specs, size of box leftover. Some places will even sell just the missing front cover, if needed, as well. Hope this helps.

[chip hayden]

lranch,thanks for the reply. it's 3ph @ 220V. the motor tag says it only draws 1.3 amps and the power cord plug is a L15-20. i'm quite sure this is how it came from the factory. i assumed i didn't want to drop one or two legs with three phase power. i just thought there might be some slick way of doing this i had no clue about.

[Franz]

If there are 6 wires coming to the switch, you need a 3 pole single throw switch because it is switching the line.
If there are 2 wires, there is a magnetic contactor or relay controlling the motor, and you need a single pole single throw switch.
For a more informative answer I'd need more information from you.

[chip hayden]

thanks Franz,
there is no magnetic contactor on this little motor and, i do have 6 wires in the switch box [3 from my power cord + the ground and, three from the motor itself ]. it appears a simple three pole, single throw toggle switch will do the trick. this unit has NEVER even been powered up. i believe someone just k-balled the switch for some other use. i have the bridgeport service manual but it doesn't show the electrics for the slotter attachment.

[Franz]

Chip, a 3pst switch will work for the switching, BUT bear in mind that there will be NO overcurrent protection for the motor in such a setup.
Unlike single phase motors, 3p motors do not have internal overcurrent protection. I'm not sufficiently conversant with the application to say if overcurrent protection to the motor would be advisable or not.

[chip hayden]

Franz,
correct me if i'm wrong but, overcurrent protection would be something to protect the motor if the load on it was too great and, the motor became overheated?

[Franz]

You get a gold star for that answer.

[chip hayden]

oooohh,thanks.