Wiring up 4 or 5 machines using a RPC?

Im just trying to figure out how I would wire up all my machines using a rotary phase converter. Is there just one wire coming out of the RPC and branch off to all the machines and have a seperate breaker at each machine,or are there multiple wires coming off of the RPC. Now when I say one wire im actually meaning one wire with 3 conductors in it.

Any advice on this would be appreciated.

Thanks Mike

There's lots of information on this if you read the archives.

There are also several ways to do it.

One simple way is to build & wire a large device box with your choice of plug style (female receptacles) and plug each machine into it. All the receptacles in the box would be wired from the initial 3 wire entry into the box. You can use one receptacle and shlepp the cable to each machine as needed, or put multiples in and run several machines at once. Ideally the wires, the rotary, and the intial input cable will have adequate protection in the system and all will have bonded grounds.

IMO, the best way is to simply set up a 3ph panel, run the rotary's output to the buss bars (L1, L2, L3), ground it and ground the system, then install a breaker for each load and wire off the breaker to the specific machine.

Shop at electrical surplus, and even "regular" scrap yards for 3ph panels, motors, and devices at huge discounts.

smt

The commercial rotary phase converters I've seen are made for just running one circuit out of them. You may be able to physically cram more wires into the terminals but there are code issues involved. I considered doing it with a terminal block and separate wires going to each machine, but ended up buying a three phase breaker panel.

I ran the single three phase circuit from the phase converter to the panel, and then from each breaker to each machine. I also put in some three phase outlets so I could plug in some machines without hardwiring them. And in addition to the three wires for three phase you need equipment ground wires.

I got the three phase Square D QO breakers used from Ebay for a reasonable price and there are probably good reasons to buy new but the used ones "seem" to work fine.

Note that I'm not an electrician and probably know just enough to be dangerous There are a lot of safety and code questions and even if you have to pay for an hour's consulting time it's a good idea to get an industrial electrician to come out and look your shop over and draw up a sketch of how you should do it and with what wire sizes.

For a small installation one can put multiple receptacles daisy chained along, with
cord drops to plug in each machine. Size the conductors so that the are correctly
protected by the breakers feeding the converter, the individual cord caps on the
pigtails serve as the individual machine disconnects.

A small three phase distribution panel does do a very nice job and is an excellent
way to go if you have more than one or two machines.

Jim

I too ran a 10hp RPC output to a new three phase panel, I bought used three pole breakers from a local used circuit breaker shop for less than half of new prices with a one year guarantee. One area I still wondering about is when I ran my rpc output wires #6 size to the panel lugs, I then ran a 30 amp breaker with #10 wire to my 5hp lathe, which draws 15 amps. I had trouble getting the lathe to start in the highest rpm setting, the RPC manufacturer told me to run the the #6's to the lathe, that he didn't usually recommend using a panel in between the RPC and the device, so I installed a 50 amp and #6 to the lathe and it worked.
I still see lots of pics of guys using the panel, I just wondering if there's something I'm missing or this is the way it plays out ?

I've got a home brewed phase converter I built from a 60 HP motor using a couple banks of caps to balance the legs. I take the output from this RPC and run it to 4 bussbars (3 hots and a ground). This busbar distributes power to 3 or 4 fused disconnects, and another 3 phase panel. I use the panel to distribute loads to the individual circuits, each of which are fuse protected.

New 3 phase circuit breakers are insanely priced, but panels and C/B's are very cheap on EBAY. For outlets 3 phase stuf is spnedy, so I typicallu use 4 wire 30 amp dryer plugs and receptacles which are availablke at any Home Depot and reasonably priced.

Years ago I found a 3 phase plug that was absolutely identical to a dryer plug. Same manufacturer, same part number. It was like $64 at the commercial electrical outlet as a 3 phase plug, and around $6 at Ace hardware as a dryer receptacle....

Stuart Caruk said:

I've got a home brewed phase converter I built from a 60 HP motor using a couple banks of caps to balance the legs. I take the output from this RPC and run it to 4 bussbars (3 hots and a ground). This busbar distributes power to 3 or 4 fused disconnects, and another 3 phase panel. I use the panel to distribute loads to the individual circuits, each of which are fuse protected.

New 3 phase circuit breakers are insanely priced, but panels and C/B's are very cheap on EBAY. For outlets 3 phase stuf is spnedy, so I typicallu use 4 wire 30 amp dryer plugs and receptacles which are availablke at any Home Depot and reasonably priced.

Years ago I found a 3 phase plug that was absolutely identical to a dryer plug. Same manufacturer, same part number. It was like $64 at the commercial electrical outlet as a 3 phase plug, and around $6 at Ace hardware as a dryer receptacle....

Click to expand...

A dryer receptacle is not the same as a 3Ø receptacle as they are different configurations and intended for different uses, a dryer receptacle is a NEMA 14-30R 30A 125/250V which is line,line,neutral & ground, a 3Ø is a NEMA 15-30R 30A 250V 3Ø which is line,line,& line + ground. Electrical work is not a place for sloppy work because it costs too much for the correct materials, a legit way to save some money is to shop Ebay or surplus dealers.

A dryer receptacle is not the same as a 3Ø receptacle as they are different configurations and intended for different uses, a dryer receptacle is a NEMA 14-30R 30A 125/250V which is line,line,neutral & ground, a 3Ø is a NEMA 15-30R 30A 250V 3Ø which is line,line,& line + ground.

Click to expand...

Is there any functional difference or any potential actual electrical issues with using the neutral connection in a dryer receptacle for the third leg of a three phase system? This is purely an "academic" question out of personal curiosity.

Thanks,

Bob

"Is there any functional difference or any potential actual electrical issues with using the neutral connection in a dryer receptacle for the third leg of a three phase system?"

This is and has been forbidden for decades.

Only heating, cooking and clothes-cleaning appliances which are designed for, and are supplied with instructions for "grounding through the neutral" (120/240 volt three-wire, grounding) are permitted to be so installed.

An exception exists for manufactured housing, including house trailers, where in addition a true ground must also be provided (120/240 volt four-wire, grounding). These appliances are essentially the same as those mentioned previously, but additionally are provided with instructions for conversion from three-wire to four-wire systems.

No equipment of any kind, excepting approved heating, cooking and clothes cleaning appliances may use these methods of grounding.

Local codes may mandate the second method, whereas the first method may ordinarily be sufficient.

"Old Work" may continue to employ the first method, while "New Work" must use the second method, unless an exception exists.

Machine tools are ordinarily 240 single-phase, grounding (three-wire) and the NEMA configuration for 120/240 single-phase, grounding through the neutral (three-wire) is different from the NEMA configuration for 240 single-phase, grounding (three-wire).


"This is purely an 'academic' question out of personal curiosity."

The NEC permits you to employ any receptacle and plug configuration which is rated for the voltage class and has the requisite number of current-carrying and grounding conductors AND as long as it is impossible to inadvertently connect the equipment of one class to a feeder provided for another class.

This gives the premises owner/operator considerable latitude.

It is customary to stick with NEMA-approved configurations, although there may be alternatives.

Local codes may mandate compliance with the NEMA-approved configurations except where the equipment was approved by a testing agency with a different configuration.

catch22 said:

Im just trying to figure out how I would wire up all my machines using a rotary phase converter. Is there just one wire coming out of the RPC and branch off to all the machines and have a seperate breaker at each machine,or are there multiple wires coming off of the RPC. Now when I say one wire im actually meaning one wire with 3 conductors in it.

Any advice on this would be appreciated.

Thanks Mike

Click to expand...

Hi Mike,
I ran 1Ph 240V through a 30A breaker, into a 3Ph disconnect, (100A!) out to a 10Hp idler, (23A, pony start) and from the same lugs, (with the idler) 3Ph out to a #6 (had the #6 conductors on hand) circuit that runs completely around my shop, with junction boxes, (deep 4" X 4") every several feet.

I wired up proper ampacity, (or greater) 4 prong, 3Ph receptacles in the few JB's that I had machines for and just pulled a loop in the rest. Have since cut a couple of these loops to wire receptacles for new machines. Any greater protection, (than the 30A feed) I feel necessary, is provided at the individual machines, making it very simple to build.

With the #6 conductors and the 100A disconnect on hand, a future upgrade will be very easy.

The alternate of course is RPC into a breaker panel with as many separate runs as you have machines, the way to go in a commercial setting but bigger conduit and lotsa' wire, though some of it can be light gage.

Being in a private, one man shop, I took the quick easy but still safe way.

The plug/receptacles serve as disconnects for all but my hard wired 17" lathe but the 100A disconnect is literally 2' from the lathes tail stock.

Bob

Peter,

Thank you for taking the time to post the explanation.

Bob

Just for yucks, I downloaded a current installation manual for a name-brand dual-fuel range.

An excerpt from that manual follows:

"This appliance may be connected by means of
permanent 'hard wiring' (flexible armored or
nonmetallic shielded copper cable), or by means of a
power supply cord kit. Only a power supply cord kit rated
at 125/250 volts minimum, 40 amperes and marked for
use with ranges shall be used. See chart for cord kit
connection opening size information. Cord must have
either 3 or 4 conductors.

"For mobile homes, new installations, recreational
vehicles, or areas where local codes do not permit
grounding through neutral, a 4 conductor power supply
cord kit rated at 125/250 volts minimum, 40 amperes
and marked for use with ranges should be used (see
Figure 5)."

The manual showed the old-style three prong "grounding through the neutral" receptacle and molded cordset for US, and the new-style four prong receptacle and molded cordset for Canada.

To the best of my knowledge, the NEC has removed the exception which allowes
grounding through the neutral for these appliances.

New installations can NOT do this, they must use four wire cordsets to the best
of my knowledge.

Jim

"To the best of my knowledge, the NEC has removed the exception which allowes grounding through the neutral for these appliances."

I haven't read that particular section of the newest NEC. The 2005 is the latest one I have.

The paragraphs I quoted are from the most current (2009) installation manual for an approved appliance.


"New installations can NOT do this, they must use four wire cordsets to the best of my knowledge."

"New work" is indeed four-wire, unless otherwise permitted by the AHJ.