220 3ph question

[bobj49f2]

I bought a lathe that is run on 220 3ph. I only have 1ph power in my shop so I am using a rotary phase inverter. The inverter is free, it belongs to my customer who uses it to set up control systems in my shop before we ship them out to the end customer. It's rated for 5hp, my lathe has a 3hp motor.

I went to wire the lathe tonight and opened the fused disconnect box on the lathe to fine a two fuse disconnect. The first fuse if for the black wire, white wire goes to a buss bar between the first fuse and second fuse, which has the red wire going to it. The 3 legs are then run to control panel below and terminated in a terminal strip. From the terminal strip the wires are wired into a reversing motor starter. From the bottom of the starter the wires are run to the motor.

I wire industrial control system for a living and have probably wired a couple of hundred 3 phase motors but I've never seen something like this. I'm assuming this lathe might have been wired to an old design transformer. My question is about the white wire, it's not fused, is it a neutral? The wiring diagram that came with the lathe shows 3ph wiring for the motor that I am used to seeing, L1, L2, L3. The diagram doesn't show the fusing just the power coming into the reversing motor starter.

I will have to get a 3 pole fuse disconnect wire the lathe like I would normally wire a three phase motor, just wonder what the white wire did. Is this a normal old way to wire a 3ph motor?

 

[miner]

So you are saying one leg is not fused. Instead it is connected by a buss bar. The disconnect should say if it is a 3 or 1 phase disconnect. It sounds like a 1 phase fused disconnect with the neutral terminals used for one of the three legs. The white wire is not neutral, though. In the end, it probably doesn't matter, those fuses don't really protect the motor. That is done by the heaters on the starter.

 

[wyliesdiesels]

If the lathe is for sure 3ph and one leg(white wire) is not fused, then it was most likely hooked up to a corner grounded delta system, where one phase leg is grounded and is thus considered a neutral! You should never fuse a neutral regardless of # of phases, so that's why 1 of the phases is unfused. Corner grounded deltas were popular back in the day because it provided a means to ground an electrical system without having to change the service drop from triplex to quadraplex. No utility I know of still offers corner grounded delta service....if CGD is desired, it would be load side derived!

What I would do is put a fuse in-line with the white wire, unless your rotary has one phase grounded(which I doubt!)

So you are saying one leg is not fused. Instead it is connected by a buss bar. The disconnect should say if it is a 3 or 1 phase disconnect. It sounds like a 1 phase fused disconnect with the neutral terminals used for one of the three legs. The white wire is not neutral, though. In the end, it probably doesn't matter, those fuses don't really protect the motor. That is done by the heaters on the starter.

A lot wrong with this comment and it sounds like you're just guessing. If its single phase, then there would only be 2 legs NOT 3(neutral doesn't count) and 240v motors, regardless of phase, do not need a neutral so there would be no reason to bring a neutral into a disconnect for a motor. And white in my world means neutral unless someone forgot to tape it. So, if its single phase but the white wire is not neutral and there's already a black and red leg, what is the white wire for then? EGC? If so, then it should be green NOT white!

 

[bobj49f2]

I got to thinking about this and I think what might have happened is someone just might have used a two fuse box because it was easiest to get. Maybe someone figured as long as two legs were fused that's was good enough. It could also be the old way of wiring the machine but I've seen a lot of hacked up wiring jobs in my 20 years of building and installing industrial machinery, most if not all by plant "electricians".

I have a three fuse box on order.

 

[wyliesdiesels]

U sure it wasn't hooked up to a corner grounded delta system?

 

[bobj49f2]

U sure it wasn't hooked up to a corner grounded delta system?

I could have been. The guy I got the lathe from got it from an old factory in Milwaukee. Anything is possible. I hooked it up to my rotary convertor last night with the straight through feed set up and it worked fine. I just wanted to see it spin.

 

[robinmbers]

yeah,A lot wrong with this comment and it sounds like you're just guessing,thanks for your sharing

 

[bobj49f2]

yeah,A lot wrong with this comment and it sounds like you're just guessing,thanks for your sharing

What?!!!

 

[wyliesdiesels]

What?!!!

I was thinking the same thing!