RPC Help needed, regarding wire and breaker

Hello all, just purchased a 5hp rpc off ebay, and she has arrived. I do need some help installing if you all dont mind. The few questions I have are as follows:

What amp breaker am I looking at in my box to power the RPC?
What gauge wire needs to run from that breaker to the RPC?

I will be powering a 1HP hardinge, and a 2hp gorotn mill for this. What gauge wire should I run from the RPC to the machines?

Your help is much appreciated!

I would put that set up on a 30 amp line with #10 wire. at the box, the breaker protects the wire to the equipment.

The equipment should have it's own protection. That is the Hardinge and the Gorton might have a fused safety box at it's connection. (Within direct sight and accessible to the operator)

Hardinges ... depending a lot on when they were made.

Pre-WW-II, almost all lathes and mills had a simple drum switch motor controller, and no motor protection whatsoever. Actually, two drum switches: one to select forward, off/brake, or reverse, and one to select high speed (about 3/4 HP) or low speed (about 3/8 HP).

Starting after WW-II, Hardinge incorporated a magnetic motor starter on many of its models, but that starter was sized for the machine's highest speed, hence the machine's highest HP, and did not protect the lowest speed, hence the lowest HP.

For the ultimate in protection, fusible safety switches should be installed at each machine. "Lock-out/tag-out" should be provided (as is provided on most such switches).

In this case, I would run #10 all the way from the panel to the conduit boxes serving each machine (see another, related thread on making one's own "bus way"). Then #12 from each conduit box to each machine's safety switch. Should a machine have a rated load greater than 16 amps, but up to 24 amps, then I would run #10 from that machine's conduit box to the machine.

"...In this case, I would run #10 all the way from the panel to the conduit boxes serving each machine (see another, related thread on making one's own "bus way"). Then #12 from each conduit box to each machine's safety switch."

A minor point if I may. Even if the machine's overcurrent protection, at the machine, is sized for 20 amps, the conductors
from the conduit box to the machine, still need to be sized for the *up*stream overcurrent protection. In this case
they'd have to be all number ten, except down stream of the overcurrent protection (rated 20 amps) inside the machine.

For example in my setup, it's a 15 amp breaker in the panelboard. Nothing under number 12 wire downstream of that,
even though I could in principle have gone with 14.

In this case a 30 amp branch circuit would be the way to go, and until it hits any overcurrent protection under 30 amps,
it has to be number ten wire all the way. A twist lock connector makes an excellent disconnect between the drop and
the machine.

jim rozen said:

"...In this case, I would run #10 all the way from the panel to the conduit boxes serving each machine (see another, related thread on making one's own "bus way"). Then #12 from each conduit box to each machine's safety switch."

A minor point if I may. Even if the machine's overcurrent protection, at the machine, is sized for 20 amps, the conductors
from the conduit box to the machine, still need to be sized for the *up*stream overcurrent protection. In this case
they'd have to be all number ten, except down stream of the overcurrent protection (rated 20 amps) inside the machine.

Click to expand...

Actually, section 240 allows "taps" from a "feeder", and puts no restriction on the wire sizes that may be considered a "feeder" (i.e. no limitation to 1/0 and above or some such). While it may be expected that it would not be used for small wire, that is not prohibited, and the definition of "feeder" puts no restriction on it either.

The "tap" must be no longer than 25 feet, must be in raceway (conduit, etc) , must have ampacity no less than 1/3 the "feeder", and must terminate in circuit protection rated for the tap ampacity.

A fused safety switch at the machine would meet that requirement, IMO.

So for a #12 "tap", limited to 20A, the "feeder" could be, for instance, 75C rated #6 protected at 60A. Then, #12 could be tapped off of it and run in EMT, IMC, or RMC to 20A safety switches on the wall at the machine.

You could NOT, for instance, use NM cable for the tap, but using it probably would already violate the "exposed to damage" clauses, so you wouldn't do that.

"A minor point if I may."

Check the "tap rule", in detail.

The approach which I proposed is acceptable under the "10 foot tap rule", 240.21(B)(1), and in some cases under the "25 foot tap rule", 240.21(B)(2).

Using a cordset (whether twist-lock or any other configuration) as a disconnect is permitted for loads 2 HP and under, only.

Thanks - I learned something today.