Wiring a three phase circuit

[Frank Keeney]

If you are talking about your first drawing which includes a subpanel, then the wire from the sub to the machines can be sized smaller; 10/3 is fine for 30 amps and 12/3 is fine for 20 amps. The smaller wire is OK because it is protected by the appropriate breaker in the subpanel. Note: the wire between the RPC disconnect and the subpanel will need to be #4 copper because of the 100 amp fuses in the disconnect.

In the second drawing, which has no subpanel, all the wires really should be #4 copper, again because of the 100 amp fuses in the disconnect. Alternatively, you could replace the fuses with lower rated ones to allow the use of smaller wire. I think you'll likely find that the savings in wire cost will go a long way toward paying for the subpanel and breakers. Plus you'll need a bunch of split bolts, which aren't too expensive, or polaris connectors (much easier to use than split bolts, but way, way more expensive). Plus, it is *so* much easier to work with 10 and 12 gauge wire. Your conduit sizes will be bigger and that adds expense.

Just make a quick parts list for each option including all the little bits because they add up quick; I'll bet the subpanel approach won't cost much more or may be cheaper.

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I'm not 100% sure I need a 40amp instead of a 30amp but assuming either plugs/receptacles or J boxes, how am I tracking so far?

[Frank Keeney]

I just bought 6 ga and 10 ga wire by the foot (from a local electrical supply house ie: not the box store) and 6 ga was 4 times the price per foot as 10 ga...just for reference. That much a price difference per foot can really add up around a shop to multiple locations...plus the fact that I don't think #6 is what you'd want in this case anyway. It would need to be #4 (even more $) or change the fuses to lower amps in the disconnect...trust me when I say you do not want to be wrestling #4 or #6 wire all around your shop and making up junction connections in a box on every machine. That's ludicrous to me compared to just making up a proper sized cord/plug into the right receptacle on breakers.

Just buy a couple of the correct amperage/style 3 pole breakers that will fit whatever subpanel you select. This is not that expensive and not where you want to skimp and try and save a few $ with connecting double and single poles with zip ties, imo.

I have had good luck with used / refurbished 3 phase twist lock receptacles and plugs from both eBay and Amazon. Better prices and availability than my local supply houses typically, who generally would have to order in what I wanted anyway.

No offense...you keep asking for advice and we keep giving it, though it may not be what you thought you wanted to hear initially.

I want to hear any and all opinions, no offense taken at all. I am here to learn! I appreciate advice!
see my latest post. I abandoned the idea of skimping on breakers and trying the original idea. Sub panel it is. Wire gauge I think is correct in latest post diagram, if not please advise lol. Still not 100% solid on whether I need 40amp breaker for those, maybe 30amp for the two machines?

[Paul F Franklin]

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I'm not 100% sure I need a 40amp instead of a 30amp but assuming either plugs/receptacles or J boxes, how am I tracking so far?

Yep, on the right track. If you need 40 amps you'll need to go to 8ga wire. Running multiple machines off a feeder like you show is not unusual in industry--provided each machine has a disconnect and an overload, which I believe you said at the beginning is the case.

IIWM, I'd probably go with individual circuits and feed to each machine, but that's mostly preference. If all the runs are in conduit, you can upsize the conduit a bit, and then down the road, should the need arise, it would be easy to pull another circuit or two.

[Phillip Mitchell]

I want to hear any and all opinions, no offense taken at all. I am here to learn! I appreciate advice!
see my latest post. I abandoned the idea of skimping on breakers and trying the original idea. Sub panel it is. Wire gauge I think is correct in latest post diagram, if not please advise lol. Still not 100% solid on whether I need 40amp breaker for those, maybe 30amp for the two machines?

I can't view the attached photos on this site as I have let my subscription lapse and not yet updated it.

To determine what size circuits (and breakers/wire/etc) you need, you need to go off the FLA (full load amps) of the highest machine motor loads. Looks like your highest amp loads are the 9 hp and 7.5 machines. The motor tags should tell you amps / FLA but I would assume the 9 hp motor is somewhere around 22-25 amps (3 phase and assuming 240v) The 7.5 hp motor will be less than that. I would put both of those machine on a 30 amp circuit (and use 10/3 wire)

Assuming the same (3 phase and 240v) for the 5 hp and under motors, these should be fine on a 20 amp circuit with 12/3 wire.

No reason to go 40 amp and 8 ga wire unless you foresee getting a machine in the ~15 hp range in the future and are future proofing for that event.

[Frank Keeney]

I can't view the attached photos on this site as I have let my subscription lapse and not yet updated it.

To determine what size circuits (and breakers/wire/etc) you need, you need to go off the FLA (full load amps) of the highest machine motor loads. Looks like your highest amp loads are the 9 hp and 7.5 machines. The motor tags should tell you amps / FLA but I would assume the 9 hp motor is somewhere around 22-25 amps (3 phase and assuming 240v) The 7.5 hp motor will be less than that. I would put both of those machine on a 30 amp circuit (and use 10/3 wire)

Assuming the same (3 phase and 240v) for the 5 hp and under motors, these should be fine on a 20 amp circuit with 12/3 wire.

No reason to go 40 amp and 8 ga wire unless you foresee getting a machine in the ~15 hp range in the future and are future proofing for that event.

Very nice, that's what I was thinking. I will double check the motor plate on the planer. The HP might be in Kw so I need to verify that. I purchased it as a 9hp.
Shaper motor plate has FLA at 20A, Table saw and RAS were at FLA 13A, and the Jointer at FLA 7.3A. I agree with the 30amp and 10/3 and 20amp 12/3 suggestion. Is there a general consensus on what plugs and receptacles are economical, common brands? What are the different styles? I think my RAS has a plug on it, I guess I could match the others to that and install receptacles to match. I assume if I need to replace the wire between the plug (to make it longer) and contactor that the same GA wire would be used?

[Jim Becker]

As far as the shekels go, in your opinion, does it seem like the breaker sizes I calculated are correct in the diagram with the sub panel for each machine run?

I wish I could give you a qualified answer but I have no experience with three phase nor the machines you have. That said, the amperage of the motor(s) on a given machine will be your guide as to what the circuit amperage needs to be for that tool (remember, it has to be at something like 80% so something that actually draws, say 18-20 amps, has to be size larger, typically at 30 amps. Once you determine the amperage, you can then size your wire for the circuit. Etc. So if you did these things, your numbers could be correct...

[Bill Dufour]

Wiring terms are confusing. For cable 10/3 means 3 insulated conductors and one ground wire. In a rubber covered cord that would be two insulated conductors and one ground. To mate with the 10/3 house wire you would need 10/4 cord.
Home depot does not carry 10/4 cord but I have bought some from the cutoff rack? They have to figure out a price to charge me. Often it is avery good price, sometimes not worth their asking price.
BilL D

[Curt Harms]

There's another aspect that favors doing things the accepted/industry standard way. If god forbid you have a fire, your insurance company might take a look at possible causes. If you did things "the way you're supposed to" you shouldn't have a problem. If you get 'creative' and that may have contributed to the fire, the insurance company could say "Sorry Charlie" and you'd have an (expensive) fight with them.

[andrew whicker]

According to NEC, you can use breaker handle ties only for 2 pole out of two single poles.

They do NOT seem to meet code for 3p

[Rollie Meyers]

I researched this recently for my shop, when selecting wire it’s my understanding that it’s important to take into consideration the temperature rating and de-rate accordingly. I had been selecting 90c insulated THHN and using 90c current ratings. I was advised to find out the current rating of the equipment connectors and breakers and de-rate the wire according to that.

In additional to that I believe NEC code requires a 20% safety margin. So for my situation, which draws less amperage than a 20hp unit I ended up using 1/0 wire on the 1ph side.

The only time the 90°C column can be used is for derating, no equipment is rated to use the 90°C ampacity, there is more to it that I have no desire to get into.

[Rod Sheridan]

You can install a 3 pole fused disconnect switch at the output of the converter, then run suitable wire to a junction box near each machine, or use a splitter at the load side of the switch and runs to each machine.

I doubt if you would need larger than 10AWG unless you have very large machines, which would mean 30A fuses.

Regards, Rod

[Jonathan Jung]

Frank, I just finished setting up 3 phase from a 30hp RPC. I decided to do it the "right" way, feeding into a 3ph load center with breakers and circuits going to outlets. I have 4 outlets throughout the shop - 10amp 480v from a step up transformer, 20amp, 30amp, and 50amp. I'm really glad I did it this way. Everything is organized on one wall - the RPC and control panel, the load center, transformer & disconnect, and circuits going out. Now it's easy to unplug a machine to move it, bring in a new machine and quickly plug it in to test it, and have protection for each machine.

It doesn't cost that much. Breakers I get on eBay, $20 each. Load center was about $200 new. For 10-30amp circuits you can use 10-3 w/g Romex (4 conductor) which is about $1.25/ft.

[Michael Zerance]

Frank, I just finished setting up 3 phase from a 30hp RPC. I decided to do it the "right" way, feeding into a 3ph load center with breakers and circuits going to outlets. I have 4 outlets throughout the shop - 10amp 480v from a step up transformer, 20amp, 30amp, and 50amp. I'm really glad I did it this way. Everything is organized on one wall - the RPC and control panel, the load center, transformer & disconnect, and circuits going out. Now it's easy to unplug a machine to move it, bring in a new machine and quickly plug it in to test it, and have protection for each machine.

It doesn't cost that much. Breakers I get on eBay, $20 each. Load center was about $200 new. For 10-30amp circuits you can use 10-3 w/g Romex (4 conductor) which is about $1.25/ft.

I have my 40hp RPC setup similarly. I used three circuits; 20amp, 30amp, and 60amp. The 30 and 60 are dedicated to individual machines and the 20 has multiple outlets throughout the shop for the smaller equipment. I am happy with the results and I have confidence that it can be used safely.

Picture taken prior to installing the idler motor:
20230605_235954.jpg

[Frank Keeney]

I have my 40hp RPC setup similarly. I used three circuits; 20amp, 30amp, and 60amp. The 30 and 60 are dedicated to individual machines and the 20 has multiple outlets throughout the shop for the smaller equipment. I am happy with the results and I have confidence that it can be used safely.

Picture taken prior to installing the idler motor:
20230605_235954.jpg

gorgeous work sir

[Frank Keeney]

Frank, I just finished setting up 3 phase from a 30hp RPC. I decided to do it the "right" way, feeding into a 3ph load center with breakers and circuits going to outlets. I have 4 outlets throughout the shop - 10amp 480v from a step up transformer, 20amp, 30amp, and 50amp. I'm really glad I did it this way. Everything is organized on one wall - the RPC and control panel, the load center, transformer & disconnect, and circuits going out. Now it's easy to unplug a machine to move it, bring in a new machine and quickly plug it in to test it, and have protection for each machine.

It doesn't cost that much. Breakers I get on eBay, $20 each. Load center was about $200 new. For 10-30amp circuits you can use 10-3 w/g Romex (4 conductor) which is about $1.25/ft.

that is very reasonable!