breaker trip on ground fault

[serb]

Elevator motor is fed through the controller, isolation transformer and disconnect switch in the elevator room. It's DC motor. Power source is in the load center and protection is done with 800A GE power circuit breaker equipped with SST trip unit. SST has rating 300A and is tapped at 225A for elevator protection. After eletrician pulled equipment grounding conductor between elevator controller and disconnect switch ground fault protection tripped the breaker in the load center. It's 3ph, 3w load center fed from transformer delta-star grounded. Ground fault settings is set for 0.6 at the SST unit.

 

[Snoball]

I don't know what you did electrically, but SST trip units are pretty old. Can you provide drawing?

 

[serb]

Unfortunatelly I don't have a drawing of SST.

 

[swn1]

After pulling a grounding conductor you get a GF trip. Sounds like a ground fault that was previously undetected due to lack of proper equipment bonding.

Your description of the circuit is a little vague, is the controller a drive or a full-voltage starter? Is the breaker on the primary or secondary side of the isolation transformer?

Some early electronic trip units are susceptable to RF interference, causing nuisance trips. This does not sound like an interference case.

The ground fault may be benign - a lot of motor controls are built with sloppy neutral / ground segregation in the control wiring. How is control power derived?

 

[dewone]

How do you know the GF tripped you. On the first version of SST there are no indicators, on the second design there are indicators. Makes that an easy call.
Is the SST a four wire, or the 3 wire.