Electric motor failure

Reply

  #1  
Old 10-31-12, 12:29 PM
Member
Thread Starter
Join Date: Oct 2012
Location: United States
Posts: 6
Electric motor failure

The 1.5 hp 220v, motor on my table saw failed recently. When it failed, one of the ground wires in the saw switch (the on-off switch) melted the metal where it was attached to the saw frame. When the motor shop looked inside the motor they said they found some melted insulation and that the windings "failed at the ground".

The motor shop didn't think the motor failure and the switch were related ( I just told them that smoke was coming out of the switch. I didn't yet know it was the ground wire.).

Any ideas as to what actually happened would be appreciated.
 
Sponsored Links
  #2  
Old 11-01-12, 04:36 AM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,968
Welcome to the forums! When the stator failed, it most likely failed big time, enough to reach the casing of the motor, and thusly travel to the switch, which was the weakest point. What size breaker do you have this puppy hooked to?
 
  #3  
Old 11-01-12, 06:14 AM
Member
Thread Starter
Join Date: Oct 2012
Location: United States
Posts: 6
Hey, thanks for the reply.

The saw is on a dedicated 60amp circuit.
 
  #4  
Old 11-01-12, 07:44 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,646
The saw is on a dedicated 60amp circuit.
What is the full load amps of the saw?
 
  #5  
Old 11-01-12, 09:18 AM
Member
Thread Starter
Join Date: Oct 2012
Location: United States
Posts: 6
The Amp load is 8.0-7.4 @208-232v. Am I correct in thinking that I could run this on a 15 amp circuit? This is the only device on this circuit.

The reason this circuit has a 60amp breaker is that it was originally used for an electric hot water tank. When I set up the saw I simply installed a 220 outlet on the circuit.
 
  #6  
Old 11-01-12, 09:26 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,646
Am I correct in thinking that I could run this on a 15 amp circuit?
Yes. That is why the switch burnt. It should never have been on a 60 amp circuit. In fact the motor might have survived on a 15 amp circuit.

I suspect though it is a 30 amp circuit because a residential storage type water heater should be on a 30 amp breaker. You didn't add the two 30s on the breaker handles to get the sixty you gave did you? Regardless it needs to be changed to 15 amps. You should not try to use the circuit till you do.
 
  #7  
Old 11-01-12, 09:38 AM
Member
Thread Starter
Join Date: Oct 2012
Location: United States
Posts: 6
Yes, I did add the two 30s on the breaker...

Thank you so much for explaining this to me. I installed a new motor, but did not want to use it until I was sure about this. Should I also change the wire to 14 gauge?

I got 7 years out of that motor, so I guess I was lucky.
 
  #8  
Old 11-01-12, 10:55 AM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,368
No, you should NOT change the wiring to #14. You should have no less than #10 on a circuit protected at 30 amperes UNLESS it is a hard-wired motor circuit AND the motor has supplemental overload protection.

My feeling is that the motor most likely developed a ground fault and that in turn caused excessive current flow through the switch, damaging the switch. Are you using a switch rated for the motor horsepower or just a heavy-duty light switch? Does the motor have a built-in overload control or a separate overload control or no overload control at all?
 
  #9  
Old 11-01-12, 01:41 PM
Member
Thread Starter
Join Date: Oct 2012
Location: United States
Posts: 6
No Furd, the question about 14 g wire was in reference to changing the breaker to 15A, but I will leave the 10g anyway.

The switch is rated to the motor.

The original motor had no overload control. The new one has a built-in overload control.
 
  #10  
Old 11-02-12, 08:55 AM
Member
Thread Starter
Join Date: Oct 2012
Location: United States
Posts: 6
Just want to update this thread.

I replaced the 30A breaker with a 15 A and left the #10 wire in place. Everything runs fine. In fact, the new motor is quite an upgrade to the original.

Thanks for the excellent help.
 
  #11  
Old 11-02-12, 03:12 PM
Nashkat1's Avatar
Member
Join Date: Mar 2012
Location: USA
Posts: 8,470
Glad you got everything working, and thank you for the feedback.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'