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Servo Motors/Drives with a Disconnect Switch?

8210 Views 3 Replies 4 Participants Last post by  Peewee0413
Hello everyone,

I was wondering what are the ramafications of placing a disconnect switch in between a servo drive and servo motor? I was thinking that any sudden disconnection of the servo drive can cause induction issues/voltage spikes?

Is there any issues with an isolated disconnect switch between this connection? in terms of noise? cable integrity? performance issues (of servo drive or motor)? safety concerns? issues with control? loss of efficiency?

thanks in advance
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· Moderator
18,681 Posts
Absolutely. Never* place any kind of switch on the load side of any VFD or servo controller.
Now, you will hear from others the NEC requires a disconnect at the machine/motor and that is true.
I personally do not like to interrupt the drives output in any way, including the blades of a disconnect.

If you must do it. Do it with a logic circuit that ensures the servo control is powered down before you can open a switch on the load side.

Best case scenario is the OCPD is lockable and in direct sight of the servo motor.
This will allow locking, but preserve the direct connection between the drive and the motor.

* Subjective comment.

· Registered
181 Posts
Wouldn't put a disconnect between servo amp and motor.
To meet US regs, we have put disconnect switches adjacent to VFD-controlled motors. Since this can damage the VFD if it is driving the motor when switched, we would use an early break aux contact to signal the drive to shut down ahead of the break in the motor circuit.
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