I have a milling machine 3 phase. 3 wires for phases,black neutral and an earth. Wire it up to a 4 pole plug??

Question

I have a milling machine 3 phase. 3 wires for phases,black neutral and an earth. Wire it up to a 4 pole plug??

Answer 1

Since you use the term "earth" you are most likely in Europe so you certainly cannot use the earth as neutral so don't be guided by someone in the US where they have a problem distinguishing between the two.

Ideally you need a 5 pin plug with neutral wired but there is a way around it. There must be some control power taken from one phase and neutral. You can buy a transformer (415/240v) and mount in it in, or adjacent to the machine. It will need to be fused. This shouldn't be a big cost especially compared to running a neutral if the panel is remote.

Answer 2

If the machine is wired with a 5 core cable then it needs to be connected via a 5 pole plug and socket. In europe they are specified as BS EN 60309-2  which replaces the old BS 4343 industrial plugs

see websitew below

A 5 pin plug and socket combination has pins for 3 phases plus a neutral plus an earth. Labelled R1/l1 S2/l2 T3/l3 then N and finally earth (this is the largest pin)  

Answer 3

Three phase motors do not require a neutral connection. The machine could have some auxiliary equipment or an electronic motor control unit that requires a neutral, but that would probably mean that some component requires single phase power at the line to neutral voltage. Since earthing conductors are not supposed to carry current, it would not be proper to connect the machine neutral to the earth conductor, but the machine might work if you make that connection. For that to work, your three phase source would need to be supplied by a wye (star) source that has a solidly grounded neutral.

The best way to deal with the problem would to have an electrician or electrical technician examine the electrical diagrams for the machine or trace the wiring to verify what is required. If the neutral is required, a 3-phase supply with a neutral should be installed. The machine may have been intended to be installed with its own isolation transformer.

Answer 4

red,blue,and white are phases,black is common.

if the motor runs backward,swap any two phase connections.

green is earth ground