advise on 3 phase wiring

[Bob Cooper]

I'm getting ready to start wiring the new shop and i need to wire it for 3 phase. I have a 5 HP RPC that i've been using in my basement and it's been dedicated to a single machine but i've got 2 more pieces of 3 phase equipment just sitting in storage waiting for the new shop to get completed. The RTC will be located in the room beneath the shop.

In the past i had the RPC wired directly to the breaker so to turn it on i would (1) flip the toggle switch on the RPC on 'on' (2) turn on the breaker (3) flip to toggle switch off.

I guess my biggest question is how to wire the 3+ devices together? I don't recall what gauge wire i used but i'm assuming something like 10 gauge. Anyway...I assume i'd run the wires in a daisy chain like manner just like 110V outlets that share a common breaker. If so it would seem that at each of the junctions where a machine needs to be connected i'd have to join 3 good size wires together...i don't really see wire nuts as the right approach here.
So what would you use at each of the locations where a machine needs to be located? Is it advisable to have a breaker of some type – I’m thinking like what you have on outside of a house for hvac – at each unit? Do these units allow you to connect 3 large gauge wires together…do they have lugs?

[Todd Burch]

For my 10HP RPC, I installed a bus-bar enclosure next to the RPC, and the RPC feeds the bus bars. Each machine's line then starts at the bus bar enclosure and goes to the machine and terminates at the plug.

I installed a 110 light switch to my RPC. When I flip on the 110 switch, a contact relay closes and turns on the RPC. I have a second 110v light switch for a second contact relay that turns on the 3PH dust collector. Works pretty nice. I have to remember to turn the RPC on first, and I know this, but visitors to the shop just don't get it. To turn on, GREY SWITCH FIRST, THEN WHITE. Turn off in opposite order.

You have to be careful though (duh), as when the RPC is off, and even the breaker for the RPC is off, there is still live line voltage at each machine's plug (the other 2 110v legs). When you forget this, and move a machine and need to move it's plug... you can generate a very loud POP and a very blue light if you are not paying attention. DAMHIKT. Scared the crap out of me.

The 3 phase plugs aren't designed to be daisy chained. I would not do it. I believe I spec'ed out the amperage of each machine and used the appropriate gauge wire.

Each machine also has its own throw switch with fuses just prior to its plug. So, between the bus bar enclosures, the contact relay enclosures, the throw switch/fuse enclosures - I have a lot of enclosures in the garage. Probably just under $1K in boxes and wires and conduit and connectors for the RPC and three 3PH machines. Maybe overkill, but it's been working flawless for 8 years now.

Todd

[Scott T Smith]

Bob, I've had a couple of shops with several pieces of 3 phase equipment that operated off of a 30 hp phase converter.

IMO, the best way to wire is to install a 3-phase load center and wire the equipment properly (with appropriate breakers / disconnects sized to the equipment). You can find some good deals on used 3-phase load centers on e-bay and craigs list.

Feed the load center with your phase converter, so that when the phase converter is running the entire load center is hot, as is all of your equipment.

The phase converter is fed by a 3 phase disconnect switch. L1 and L2 incoming to the disconnect are from a 240VAC breaker in your regular single phase panel (sized for the amperage required by the RPC). L1 and L2 output from the disconnect feed both the power requirements for the phase converter, as well as L1 and L2 incoming to your three phase load center. The L3 output from the phase converter feeds L3 on your 3-phase load center.

By using this system, you have proper circuit breaker protections sized to your actual machines, and when the phase converter is off, the entire 3-phase system is off as well.

[Brian Backner]

+1 on using a 3-phase breaker panel. It makes for a much safer set-up and can even be used to "stack" idler motors for increased power.

I've attached a pdf of one configuration - I got this off of the Practical Machinist chat list several years ago. It looks quite complicated at first glance, but works very well. As shown, it does not have any balancing capacitors, but these can be easily added.

Brian

[Rob Russell]

I agree with the previous posts.

I've got european stuff that's all 3-phase so had to go down that path.

The best advice is to have a separate panel for your 3-phase loads. If you're doing multiple machines, it's the best way to go. You can still do the multiple rotary convertor route.