10/4 cable hooked to 10/3 plug?

[keith ouellette]

I have 220 in my shop but not 4 wire. The saw I just bought has 10/4 cable. can I hook that to a plug that only excepts 3. do I just not hook up the red or do I combine the red with ?????

[Dan Friedrichs]

I assume the saw is just a standard 220V motor (2 hots and a ground), and the use of 10/3G (3 hots and a ground) was unnecessary (only 10/2G was needed). If so, there is nothing wrong with hooking up a 3-wire plug and just leaving the unused wire unconnected. I assume you mean that the red wire is also unconnected at the saw?

[keith ouellette]

I assume the saw is just a standard 220V motor (2 hots and a ground), and the use of 10/3G (3 hots and a ground) was unnecessary (only 10/2G was needed). If so, there is nothing wrong with hooking up a 3-wire plug and just leaving the unused wire unconnected. I assume you mean that the red wire is also unconnected at the saw?

I'm sorry I didn't give you enough info. It is a 3 phase machine (Original 5 hp RAS) and has a convertor with it. the 10/4 comes out of the convertor. My original question was also wrong. I think I meant to say leave the white wire un connected because the red and the black are both hot. So I would be hooking up black to the black from the panel and red to white from the panel. White from the machine will not be used and green is still ground.

Is that correct.

[Rod Sheridan]

I assume the saw is just a standard 220V motor (2 hots and a ground), and the use of 10/3G (3 hots and a ground) was unnecessary (only 10/2G was needed). If so, there is nothing wrong with hooking up a 3-wire plug and just leaving the unused wire unconnected. I assume you mean that the red wire is also unconnected at the saw?

Dan, in portable cable the ground conductor is counted, the poster needs 10/3 if he wants two lines and a ground......Rod.

P.S. As for the wiring Keith, without a drawing, and a look at how your motor and converter are wired, it's not possible to give a colour coded answer....Rod

[Scott T Smith]

Keith, for a rotary phase converter (RPC) it's usually wired as follows:

First, there is usually a disconnect installed in-line between your load center and the RPC, and this is used to turn the RPC on and off. Line 1 and 2 from your load center are attached to one side of the disconnect. If you don't have a disconnect, another option is to use your circuit breaker, but electricians will usually advise against this since breakers are not designed to be on-off switches.

On the other side of the disconnect, Leg 1 attaches to leg 1 on the RPC and leg 1 on the 3 phase motor.
Leg 2 from your disconnect attaches to leg 2 on the RPC and leg 2 on the 3 phase motor.
Leg 3 from your converter attaches to leg 3 on the 3 phase motor.

Ground from the load center attaches to both the RPC frame and the saw frame.

When you start the saw, if it turns backwards reverse any two of the three legs.

To start the saw, activate your disconnect and the RPC will spin up. Then, you can operate the saw from the switch mounted on it.

[Ole Anderson]

10/3 and 10/2 WG (with ground) are the same, I think unless the fine terminology of WG means a bare conductor like you would have in romex.

[keith ouellette]

Hi scott;
thanks for the explin but I still don't know which way is up.

Here is a picture of what I have on the saw. There is a small cable going from the convertor up into the arm. I think this goes to the On/Off switch on the saw (there is nothing else up there for it to go to) then the the 2 --10/4 cables that come out of the convertor; one goes to the motor and the other end is where the plug would go.

Is the thin cable that goes to the switch working as the disconnect or just the motors on off switch. Would it be correct to assume the red and black are both hot, the green is ground and the white is??? another ground?

[Chip Lindley]

Keith, why not take the cover off that static converter and let us see what's inside? The transformer mounted outside the case leads me to believe there is a low-voltage controlled contactor inside. Your saw's arm-mounted pushbuttons would control the on/off of that contactor.

If you look inside the box, you will see which wires of your 10/4 cord coming in are connected, and which wire is not.

[Scott T Smith]

Keith, why not take the cover off that static converter and let us see what's inside? The transformer mounted outside the case leads me to believe there is a low-voltage controlled contactor inside. Your saw's arm-mounted pushbuttons would control the on/off of that contactor.

If you look inside the box, you will see which wires of your 10/4 cord coming in are connected, and which wire is not.


+1 - You have a static, not an RPC. Pull the cover off and see if there is a wiring diagram inside it.

It is unusual to see a phase converter fed with 4 wires; as Chip indicated see if one of them is not used inside the converter.

[keith ouellette]

Keith, why not take the cover off that static converter and let us see what's inside? The transformer mounted outside the case leads me to believe there is a low-voltage controlled contactor inside. Your saw's arm-mounted pushbuttons would control the on/off of that contactor.

If you look inside the box, you will see which wires of your 10/4 cord coming in are connected, and which wire is not.


+1 - You have a static, not an RPC. Pull the cover off and see if there is a wiring diagram inside it.

It is unusual to see a phase converter fed with 4 wires; as Chip indicated see if one of them is not used inside the converter.

Ok there is the picture. All the wires are being used. The white wire that goes in has blue tape on the end and is connected to L1. black to L2 and red to L3. white, black and red on the other side are connected to T1,T2,T3 and then out to the motor. The wiring diagram on the cover (can't get a good picture of it) has L1,L2,L3 going to "3 phase disconnect". Like you said scott; I would use the breaker because its not going to be turned on and off a lot. I hope thats ok because a disconnect appears to cost about $100. So with the disconnect being the breaker all I need is a plug into the wall.

SO Now I need to figure out which two wires are hot? and what to do with the 3rd wire in the cable? Or am I missing something Else? Thanks for the help. Electrical is not my strong suite.

[Rollie Meyers]

That is not a phase converter static or otherwise, what you have is a magnetic starter & you need a phase converter or a VFD, BTW is your saw a DeWalt?

[keith ouellette]

That is not a phase converter static or otherwise, what you have is a magnetic starter & you need a phase converter or a VFD, BTW is your saw a DeWalt?

That is why I was seeking help before I hooked it up. I was going by what I was told by the seller. He wasn't actually the one who used the saw so there is a good chance he was wrong. If what you say is true, and I don't doubt that it is from what I have found out so far, then it will have to go back. I don't have the money for a convertor. Guess the saw was just too good to be true.

[Chip Lindley]

Now I can see! your "box" is indeed a 3-phase magnetic motor starter. The saw's up-front pushbuttons control the contactor (making/breaking incoming L1, L2, L3) with 24v coil (probably) provided by the outboard transformer. And the overload block protects the machine's motor (T1, T2, T3) with heaters sized for that motor.

Keith, you got a really great deal on a 5 hp, 3-phase, Original Saw/DeWalt! Don't give up yet. Static phase converters are not that expensive. Units for a 5hp motor are less than $100 on eBay. Cedarburg, Phase-A-Matic and Ronk are reputable names. Save your lunch money. Take long walks and pick up aluminum cans! Have a yard sale! It won't take long!

Just maybe, if you advertise your plight in the SMC Classifieds, a real bargain 5hp static converter may appear!