Cable size for 10 hp lathe

[bigearl67]

I have a 10 hp Mori-Seki CNC lathe I need to wire and would like to know what size cable I need to run. It will be about a 20 foot run from my RPC and I am hoping to be able to scrounge the cable from what I already have on hand, mostly 10 and 12 ga. Thanks, Earl

 

[Ray C]

You're looking at 7500 Watts, divided by 220 Volts, is equal to 34 Amps. Since you're running motors with potentially heavy start-up current, you need to double that at least -so, you're conservatively at 70 Amps.

If you look at this chart, it says 8 Ga will handle that load for chassis wiring purposes. Since your distance is only 20 feet, you could probably go that route assuming this is a temporary setup. If it were mine and if the setup was meant to be permanent, I would probably go with 6 Ga wire.

http://www.powerstream.com/Wire_Size.htm

Ray

I have a 10 hp Mori-Seki CNC lathe I need to wire and would like to know what size cable I need to run. It will be about a 20 foot run from my RPC and I am hoping to be able to scrounge the cable from what I already have on hand, mostly 10 and 12 ga. Thanks, Earl

 

[AlanR]

You're looking at 7500 Watts, divided by 220 Volts, is equal to 34 Amps. Since you're running motors with potentially heavy start-up current, you need to double that at least -so, you're conservatively at 70 Amps.

bigearl didn't directly say if the machine was three phase or not but he mentioned an RPC. If it is 3 phase you can divide your figures by three. I also think you're overdoing the start up current, it's short time enough that the wires won't overheat

 

[Ray C]

bigearl didn't directly say if the machine was three phase or not but he mentioned an RPC. If it is 3 phase you can divide your figures by three. I also think you're overdoing the start up current, it's short time enough that the wires won't overheat

Duh, yeah... that sounds about right. I'd be pretty comfortable with 8 Ga. then.


Ray

 

[AlanR]

Duh, yeah... that sounds about right. I'd be pretty comfortable with 8 Ga. then.


Ray

Here's the spec http://www.engineeringtoolbox.com/three-phase-circuit-wiring-d_737.html

I think 8 gauge is plenty and I might even try the 10 since he's already got it and only needs 20ft. I'd lay it out on the floor and check it with a clamp on ammeter. Check the voltage drop along the wire with a voltmeter too.

 

[Gary Max]

I ran 8 ga for my 7.5 hp compressor motor--- if my mind is still working--- I think it was $2.00 a foot.

 

[AlanR]

I ran 8 ga for my 7.5 hp compressor motor--- if my mind is still working--- I think it was $2.00 a foot.

It's not only the cost, it's also the difficulty of handling and pulling larger sizes than needed. Wrestling heavy gauge wire is not a lot of fun.

 

[Walltoddj]

Even if his is 3 phase you have to feed with 220v 1 phase, my 5 hp draws 17 amps per leg running on 3 phase 220v it's on 10ga 4 wire copper. Have you looked to see at your local Lowe's or Home depot some time the have cuts at a discount I picked up some 6ga 4 wire real cheap. One thing I found I'll never do is skimp on the wire in the end it's better larger than small.

Todd

 

[rdhem2]

Ray C is usually pretty much up to date on such things. In this case we are not concerned with wire heating. Although he failed to mention it I am sure voltage drop on start-up was in the back of his mind.

Voltage drop is one of those critters that I believe the right term is exponential. A small change up front is a increasingly big change on the backside. In other words, a problem becomes a helluva pain in the ass in a real hurry. #6 is not that big and still fits in a 3/4" pipe just like #8.

Don't go to these home improvement places. Make a few calls and I'll bet a local electrical contractor will sell you some cheap. Where do you think their beer money comes from? Even a scrap yard may have some short pieces. #6 is a pretty popular size. Don't screw yourself to save a few pennies.

 

[Ulma Doctor]

my 2 cents
the most critical wire will be from supply to the RPC, it will bear the amperage of running the system.
so long as that wiring is sufficient to the RPC, the lathe or any other ancillary equipment can safely be run on reduced sized wire in comparison to the single phase input to the RPC.
for example a short length of 10/4 would be sufficient to run a 30 amp circuit
8/4 is good up to 50 amps
6/4 is good to 65 amps