Re: Switch Smoke


I have a SB9C that runs on a single phase, 3/4hp, AC, 120+/- volt motor.

Please school me on the advantage and process of going DC.


On Wednesday, September 1, 2021, 02:24:31 PM CDT, Ondrej Krejci via <okrejci@...> wrote:


I should like to know, out of curiosity, how many people run their machine tools on direct current or with universal motors as opposed to the general norm of alternating current and induction motors.


On Wednesday, September 1, 2021, 12:15:31 PM EDT, ART <twocan90@...> wrote:


I decided to go back and check my repair to the smoking switch, and I found the real problem. 

The connection between the "tab" where the output wire from the switch connects to the motor was a riveted connection that worked loose over time.  This loose connection generated heat which heated the wire and weakened the insulation on that wire causing a short to the ground wire which was touching it in the small space of the switch housing.

Hope that helps.

Capt. Art

----- Forwarded Message -----
From: ART <twocan90@...>
To: <>
Sent: Tuesday, August 31, 2021, 04:44:02 PM EDT
Subject: Re: [SouthBendLathe] Switch Smoke


Carefully check for frayed or broken insulation on the wires that feed the switch.

I just had this exact same thing happen on my drill press.  Upon opening the switch cover, I found the positive input wire rubbing against the ground wire.  This is also the original switch, probably 20+ years old.

In any case I insulated the broken insulation and the problem was fixed.

You should also make sure that the jumper wire is the same size as the rest of the wiring.

Capt. Art

On Tuesday, August 31, 2021, 04:31:30 PM EDT, Glen Ruch via <gw.ruch@...> wrote:

Perhaps the Motor Wiring Diagrams would be of use:


On 8/31/21 3:20 PM, Glen Ruch via wrote:

Depending on the connection, it is possible the circuit is running thru the motor commutator thru the motor coil back thru the commutator to the drum switch.  The motor winding could be read as a short circuit depending on how the Ohm meter is set.

On 8/31/21 12:37 PM, G K via wrote:
When checking continuity with my voltmeter, I am showing a closed circuit between T1, T3, and T2, T4.  Is this expected, or is there an issue within the motor?

On Tuesday, August 31, 2021, 08:43:13 AM CDT, Ray De Jong via <dejongray@...> wrote:

The Jumper terminal screws may have been a bit loose and arcing occurred and the resulting heat build up probably fried the wire. I have replaced many receptacles that fried not only the lead-in conductor but also the inside of the outlet, all from contacts losing their tension an/or a loose connection

On Monday, August 30, 2021, 6:34:26 PM PDT, G K via <bug_hunter2000@...> wrote:

Working on the SB9 tonight, and smelled a little burn.  Flipped the switch off. looked around and saw no issues.  Flipped it back on and pop goes the breaker, and smoke from the switch.  I believe the switch is the original (1942) drum switch.  Unplugged it, and took the cover off the switch, and the jumper was fried.  No idea why.  I'm not an electrician, but can use a voltmeter.  Suggested troubleshoot? 

120 volt circuit. Furmas R44, 6-terminal switch, Dayton 3/4 hp motor.

I'm planning on pulling it apart tomorrow and look for any additional burned wires, but I do not believe I will find any from a cursory look.  Then I'll wire a receptacle directly onto the motor to see if there are any issues there.  If were good there, I will re-wire the switch and see what happens.  Maybe some chips got inside and caused a short.  Not sure.  Any chance capacitor went back and caused the short?  The only burn smell is in the proximity of the switch, but that could be where the smallest gauge wire (jumper) is located.



Join to automatically receive all group messages.