CH DigiTrip RMS 520 ZSI

[aderemb]

New here to the forum. I have a project to implement Zone Selective Interlock (ZSI) on a 480V bus (Y-connected) system using CH Digitrip RMS 520 LSIG. I will like to disable the "ground fault" function on the main breaker and some feeder breakers feeding the MCC and large motor downstream. We have experienced spurious ground trips in the past on this bus each time a piece of equipment is been put back in service. Has anyone have success doing this without any detrimental effect on the equipment? Any help is highly appreciated.

 

[dpc]

If you are in the US, there are NEC requirement for GF protection that you may have to comply with.

Generally, nuisance GF trips can be reduced by increasing the time delay.

David Castor

http://www.cvoes.com

 

[alehman]

It's usually not possible to disable GF if the trip unit is equipped with it.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[rbulsara]

You may need to get rid of the ZIS so that each breaker's GF pick up and time delay can be set independently.

With ZSI on, the downstream breaker defaults to minimum TD or INST (no intentional time delay). This may be the cause of some of your nuisance trips. A device with a ground fault would not always coordinate with the downstream breakers without GF.

Also have someone experienced look at the coordination.

Rafiq Bulsara

http://www.srengineersct.com

 

[rcw retired EE]

When the ZSI input is activated it raises the time delay setting of the Main breaker GF protection. If teh nput is ot present, the GF trips instantaeneously. It may be that your downstream feeder breakers are a little slow in sending the ZSI to the Main breaker or the wiring may be defective.