Cable size for 10 hp lathe

[AlanR]

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.

Agree, I was assuming the RPC was already wired to the supply.

 

[Walltoddj]

I'd have to put an amp probe on it again but if I recall my 10 RPC was 15 amps and didn't vary when I use the mill and grinder together. What size RPC are you using?

Todd

 

[Ray C]

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.

rdhem2,

-Thanks for the vote of confidence and yes, initial draw and the resulting voltage drop was foremost on my mind... To be specific, two concerns are front-and-center: 1) This is for a Mori-Seki CNC. I do not know if they already have internal VFDs or some mechanism to intelligently manage current draw. If they do not, and if they're gluttonous power hogs at all times then, my assumption was to at least double the theoretical draw at 7500 Watts (which does not even take power factor into consideration). 2) The OP said he was powering it off an RPC. In all my understandings of RPCs, they do not produce perfectly balanced 3 phase meaning that one or more legs is going to have a higher than expected current draw. -So given this, I opted to err on the conservative side and recommend a slightly heavier gauge than what is theoretically required.-

And yes, I had a "senior moment" and forgot to divide the current by 3 because this is a Y-connected 3 phase system but, I still think that 8 Ga is the way to go... Once a wire is undersized for the application, you won't know what crazy problems you'll have to troubleshoot until they start rearing their ugly heads...

The cost per foot and difficulty of managing 8 Ga vs 10 Ga is not burdensome. When you start dealing with #2, 1 and 0 gauge... yes, that's a lot harder to work with. 8 vs 10... not so much.


Ray

 

[Tony Wells]

Is that the spindle motor? It is a continuously variable motor if it is as I recall on the SL and TL series. It's been a long time, but I have rebuilt a few of the motor drives on TL-5 and SL-3 and 4 Mori's.

Don't forget to fudge a little for the servo drives on the X AND Z axes.

 

[Walltoddj]

Just a point of interest you say the initial draw on a 10 hp RHC if you use the start switch is 120 amps, if you dead start without the starter switch is 162 amps I know this because my Electrican and I did it just to see. I got this RPC cheap $300 because the owner moved and the new building had 3 ph power. I don't use it now but I'm wired on a 30 amp line and I never had a problem.

Todd

 

[bigearl67]

Thanks for all the replies, it sure does help. It is a 15 hp rpc that I have for my vmc but since Ipicked up the lathe I need to run them both on the same rpc for now. I don’t want toinstall a “temporary” line, just do itright the first time. Looks like I can run some 10 gauge SO to charge up the batteries and see how the electricalrespond (first time I fired up this machine). Then I Can put an amp meter on theline to see what the draw is and go fromthere. Eight gauge isn’t a problem, just another expense I don’t really want right now. Thanks again for all theinput. Earl


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Is that the spindle motor? It is a continuously variable motor if it is as I recall on the SL and TL series. It's been a long time, but I have rebuilt a few of the motor drives on TL-5 and SL-3 and 4 Mori's.

Don't forget to fudge a little for the servo drives on the X AND Z axes.

Yes, that's just the spindle motor. Thanks, Earl

 

[Walltoddj]

Thanks for all the replies, it sure does help. It is a 15 hp rpc that I have for my vmc but since Ipicked up the lathe I need to run them both on the same rpc for now. I don’t want toinstall a “temporary” line, just do itright the first time. Looks like I can run some 10 gauge SO to charge up the batteries and see how the electricalrespond (first time I fired up this machine). Then I Can put an amp meter on theline to see what the draw is and go fromthere. Eight gauge isn’t a problem, just another expense I don’t really want right now. Thanks again for all theinput. Earl


- - - Updated - - -



Yes, that's just the spindle motor. Thanks, Earl

If you have a welder or dryer outlet close to your RPC I'd plug it in to see what the converter draws that will give you an idea if the 10 gauge is big enough, I run at 17 amps but I ran 10 gauge 4 wire though the whole shop with outlets at each machine so I will have no cords on the floor. As you said don't want to install temporary line it maybe better to wait till the funds or time are there to do it how you would really like to.

Todd

 

[flutedchamber]

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.

When I ran 6 gauge wire to my compressor I first cut the conduit (plastic conduit) and installed the hangers and sweeps with no glue. Once I was sure I had the lengths perfect I took the conduit down and ran the wires thru it, then glued and tightened the hangers with the wire inside. A LOT easier than trying to run 4 #6 wires thru conduit that is already installed.

One word of caution though. Leave an extra foot of wire sticking out of each end of the conduit. Saves frustration later if the wire moves while you're installing the conduit.

 

[Walltoddj]

When I ran 6 gauge wire to my compressor I first cut the conduit (plastic conduit) and installed the hangers and sweeps with no glue. Once I was sure I had the lengths perfect I took the conduit down and ran the wires thru it, then glued and tightened the hangers with the wire inside. A LOT easier than trying to run 4 #6 wires thru conduit that is already installed.

One word of caution though. Leave an extra foot of wire sticking out of each end of the conduit. Saves frustration later if the wire moves while you're installing the conduit.

Take a piece of rope tie a rag to it that will fit in the conduit and suck it though with a vacuum, now tie the rope to the wire and pull it though. Did 150' of 150amp 4 wire to feed my shop if it gets tight they have a compound you can use or a light soap and water mixture. As was said leave extra to tie in I have about a 2' loop to be sure I'll always be able to get it hooked up and it cheaper to do it when you pull it than to do it again because it was short.

Todd