Radial Arm Saw Wiring Question

[Ditch Doc]

Hi all,

I'm working on an old B&D/Dewalt model 3574 radial arm saw. It is a 220V, single phase. The power cord, the cable for the switch and the cable for the motor all go to a box containing the motor control. The on/off switch at the front of the machine is busted. I can't find a replacement, so I'm wiring in another switch which will be mounted at the front of the saw under the table.

Looking at the back of the broken switch, there is a black, white and green wire. I was assuming that the switch pulls 120V out of the 240V circuit to operate the motor control. If that is the case, the black and white would be the circuit that would be closed when the switch is turned on, and the green is a ground. But looking at the motor control, the green is attached directly across from the white... Is this actually a ground or is it something else?

I don't have any experience with motor controls, nor does anyone I know. This saw ran for years like this, so I'm assuming it's wired correctly. In order to wire in the new switch in the picture, I was planning to hook in the black and white across from each other. This would be connected to the motor control in the same places the existing black and white are located. The ground would be connected to the ground screw in the switch.

Would this be correct?

Not sure if it helps, but here's shots of the plate on the motor as well as the markings on the motor control. Thanks for the help!

 

[matt_i]

I would wire it with this type of switch.

https://www.homedepot.com/p/Leviton...hite-R62-03032-2WS/100356941?modalType=drawer

Do you know the HP of the motor? I'm guessing its a 20A or less motor, the 30A switch would be conservative and handle the extra starting amperage of the blade startup. This one would be wired as the only device between the residential circuit panel (typically red, black on a double-pole breaker) and the motor itself. Grounds would be hooked to the motor frame, the saw frame, any metal boxes, and finally back to the ground lug inside the circuit panel.

It is possible that a neutral wire (typical white) is used, hooks to neutral-bar in the circuit panel and then there would be 120vac between each "hot" (red, black) and white. Most machine tool manufacturers would use a 50va "dry control transformer" to step down from 240:120 for any control voltage.

It does sound like you might have a different setup. Can you post a picture of the "motor control"? As well as the part that is broken. I did reconsider that my toggle above might have to be located somewhere non-ergonomic.

 

[Ditch Doc]

Apparently, the links to the pictures aren't working as intended. I'll repost the pics here. There is a pic of the connections on the broken switch, one of how the switch is connected to the motor control, and the rest are of the plate on the motor, the new switch, and the markings on the motor control.

 

[Ditch Doc]

I would wire it with this type of switch.

https://www.homedepot.com/p/Leviton...hite-R62-03032-2WS/100356941?modalType=drawer

That seems easy enough. I like the idea of taking the motor control out of the system completely. Sorry about the links for the pictures not working. I tried reposting them. One of them is a pic of the new switch. Would this be an option as I already have it, or would the snap switch you recommended be better / safer?

It's a 3hp, 18 amp motor. The plate specifies a 50 amp time delay fuse, but the receptacle is on a 70 amp line I ran for a couple of welders across the shop. I'm thinking that the 70 amp breaker should be able to handle the start up amperage... or is the time delay fuse absolutely necessary?

Thanks for the advice!

 

[seber]

There is no ground in that system. The off button is normally closed In this case and the start button is normally open. That controls the relay that pulls in the contacts for each side of the 220. In this case the green color is just incidental.
I would not go to a normal on off switch. Inrush current will burn it up eventually. Also, the motor controller is a safety component. If the power dies or you draw an overload, it will not come back on until you hit the start button. There is good reason the manufacturer spent extra money to do it that way.

 

[Ditch Doc]

I would wire it with this type of switch.

https://www.homedepot.com/p/Leviton...hite-R62-03032-2WS/100356941?modalType=drawer

Worked like a champ and saved me a ton of money. Huge thanks!

I also feel a lot better knowing that this switch is listed as a 30 amp motor control.