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3 Phase to Single phase saw conversion7/11
I have recently acquired a SCMI SI320 sliding table saw. It was setup as a 3 phase machine and I have since purchased a new leeson 7.5hp single phase motor. I have motor mounted and ready to go however I don't know where to go from there when it comes to the wiring. I know I can just get a magnetic switch and mount a new box on the saw and bypass the old wiring etc. (I've got the same motor setup and switch on another machine.) But I don't want to have to do that if I can somehow utilize the factory controls. Any input on 3 phase switches vs single phase? I haven't had much luck researching it. The SCMI tech said I could just rewire it but im not sure if thats the gospel, I know they sure like to sell their pricey replacement parts. Anyone that has done this type conversion please chime in.
A switch is a switch is a switch - they all do the same thing - open and close circuits.
The reason you likely will not be able to use your existing contactor is the amperage rating. A three phase, 7.5hp motor will draw about 22 amps. A single phase motor at 7.5hp will draw about 40 amps, with a start-up current draw of twice that.
Look for the amperage specs listed on your existing contactor. If it matches or exceeds your motor load specs, you're good to go.
It's unlikely your existing contactor has the amperage capability you need. And if the contactor does not have the capacity, it's unlikely any of the load-carrying wiring has sufficient capacity either. Most machines are not over-engineered to that extent.
I couldn't find my motorload chart, but I'm guessing you would need minimum 8 ga conductors (possibly 6 ga) to carry a 40 amp load, and those large conductors will need to go all the way to the breaker panel.
My guess is your saw is wired with 10 or possibly only 12 ga conductors. I would also guess that your existing start/stop switch will be useable, as that switch handles very little current.
So, theoretically I can utilize the existing switches and replaces the contractors and wiring that are behind the control panel. The circuits are confusing to me as there is a transformer back there and multiple, contactors or breaker assemblies. I don't know what does what. Who could I hire to rewire for me? Are there machinery repair people that I could search for? I don't mind paying to have it done correctly I just don't know where to start. Im pretty capable in this type of work but, I don't have the time to do things twice. I'll check the existing contactors and see what they are rated.
I have done this job many times. It is just simply a matter of following the cable back from the motor to the terminal strip. From there, you can follow the wires back to the contact and then the motor overload breaker.
The transformer is just there to downsize the incoming power to 24 VDC or 110 VAC for all the switches. You will run into problems with some of the other items depending upon how it's wired running them off single phase. Usually not. Depending upon the part of the country you are in, I am able to assist in this or recommend a local tech. The other breakers and contacts are used for the transformer and safety reasons for making sure two functions that contradict each other aren't run at the same time.
You can also usually call some local electrical companies and they will usually have a electrician able to work on industrial equipment.
Each leg of the three phase circuit will have a fuse (or breaker) to protect it. The transformer may also be fuse-protected.
The contactor has several purposes: it allows you the luxury of using low voltage Start/Stop switches to control a high voltage circuit. Also, if your power goes off while the saw is running, the saw will not restart on it's own when power is restored (a safety feature).
The transformer is probably a multi-tap version, which is necessary if you have a motor that is capable of two different voltages (eg 240/480).
It's all a simple circuit, but it can be confusing. A good commercial/industrial electrician should be able to get this saw running for you, with all the proper component ratings and circuit protections.
An electrician is bound by law to comply with code, which likely will include a safety disconnect at the machine. Some electricians have an assortment of used/salvaged components - be sure to ask.
Be prepared, this won't be inexpensive - I'm guessing $1,000 or so, as it likely will be an all day job.
First, look in the mirror and slap yourself sharply in the face...
Next... remove your newly installed single phase motor and re-install the original. Now go and exchange the new motor for a new or used rotary phase converter. (Be sure to get one big enough to run your saw and any other equipment you may acquire.)
Now begin to trade all your single phase toys for real industrial machinery.
Thanks to all the informative posters who actually posted some real know how to answer my questions. I'll be at the shop tomorrow and will check out the existing contactors and wire sizes to see what will transfer over. Also, Im in Tampa, FL if any of you know of a tech in the area I'd be glad to call them.
Jim Baldwin..... the existing 3 phase motor was fried, I have no other 3 phase machines and I do not run a production wood shop. Why in the holy hell would I by a new 3 phase motor and screw around with a phase converter? My powermatic saw with a single phase 3 hp motor has never bogged down or been underpowered with anything I have ever tried to cut. So I don't see how a 7.5hp motor thats single phase could ever be considered underpowered for this application. Maybe YOU should take a look in the mirror and quit playing with your antiquated toys and invest in a real CNC machine that would run circles around your handrail carvings.
I was just having fun (at your expense) sorry.
Actually there are quite a few good reasons to make a switch to 3 phase. The price of your new 7.5 hp motor would have gone along way towards a phase converter but not if your other motor was fried anyway.
As for your other well-aimed (and well deserved) jab, it may interest you to know that about twenty years ago I invented and built my own handrail shaping machine. The reason I don't own a 5 axis CNC is because I don't need one. I do compete regularly with companies who do though and they don't always run circles around me. I even do work for them supplying stuff they don't want to do. Almost nothing you see on my web-site was hand carved.
Sorry again for the sarcasm.
Ben, the worst thing you can do to your new motor is starve it for voltage and/or amperage - upsize your feed if you have any doubts.
Having said that, I recently installed a new HVAC system on my house. The compressor unit draws 27 amps, and the internal wiring looks to be 12 ga. I was shocked (not literally).
Maybe they've incorporated some new super-conductor material into copper wire that has increased its' capacity?? I don't know.
I know that 14 ga romex is now sufficient for a 15 amp residential circuit - it didn't used to be that way.