Post By Terry Harper
Drum Switch Wiring for a newbie
I know, I know...this has been covered probably a dozen times but....I can't seem to find an answer that works.
Here is the issue... I have a 13"x5' Southbend retro fitted from 440 3 phase to 220 single phase using a reversable Baldore motor.
Here is the wiring diagram from the motor - note its wired for High Voltage as shown on the right hand diagram:
Here is the Drum Switch:
I know iam supposed to reverse T2 & T8 but.....Whats throwing me is the center terminals. My friend who was assiting me said that this particular drum switch cannot
be wired for single phase. is he right? The switch was wired 440 3 phase and the diagram inside the box is long gone along with a model number.
Remember....Wiring and I have a love hate relationship and my understanding is limited.... HELP!!
Please tell us more about the switch. Is it a 3-pole double throw? If so, I don't see how it could safely be made to be a control switch for the single phase motor. To be safe, you have to break BOTH lines of a 240V single phase, because both wires are 120V HOT TO GROUND.
My old SB has a 4-pole double-throw switch. Two of the poles switch the two lines. The other two are wired as a reversing switch to swap the reversing leads, #5 and #8. There are SIX wires between the switch and the motor. One pair is the two Line connections. The remaining for are 5 & 8 going back to the switch and 5 & 8 returning from the switch.
Get a multimeter with a continuity function and play with the switch, make a map of what lights up with each terminal at each switch position, then reverse engineer it.
OK... I looked for more info.....Its a Cutler-Hammer Type "O" (No. 5441H27A) Vintage 1942. I believe it is a 3 Pole Double Throw.....
According to the label its rated for a 1-1/2 hp motor on 230 single phase.
That 3PDT switch does not have enough poles to safely accomplish FWD-OFF-REV for that particular motor.
Do not accept any wiring scheme which does not break BOTH poles of the 230V when the switch is OFF. It just simply isn't safe. Both sides of a 240 line are "hot to ground" by 120V.
I have ordered a new switch. Better safe than sorry!
Actually, I think you can do this with a 3PDT, and properly disconnect all the hots. The key is that there are two run coils in series. t1 -> t2 -> t3 -> t4, and the start winding needs to be in parallel with only one of those two coils, but it does not matter which one. So if you tie t8 to the t2-t3 junction, then you can reverse the motor by moving t5 from t1 to t4. You don't have to switch both t5 and t8. I'll try to draw a picture.
That should work. I'm not sure how we get it work with your motor's terminals, however.
... on further inspection, it looks like all you have to do is move 5 from the motors L2 terminal to its L1. Some others should weigh in first
I have two or three lathes wired up using 3P DT drum switches with single phase motors. Both sides get disconnected, and the motor reverses correctly. I don't remember if the wiring is exactly as Allan has shown, but it's something like that. It's been a while.
One thing to watch out for with drum switches: Some of them already have the "cross-over" wires built in as metal straps or wires that connect between the terminals. They are usually removable if you don't want them, but sometimes they are almost hidden down underneath. Make sure that you know how the switch is wired internally.
Thanks for the help folks!
I ended up changing out the switch - everything works as it should now.