Hi, I need to transfer a live load

[Victor Lee]

Hi,
I need to transfer a live load supported by a 3ph UPS source to an external maintenance bypass source. The UPS will be transferred to static bypass mode. The concern here is that the UPS source is connected to an isolation transformer (delta/star) with its neutral earthed. The external maintenance bypass source is taken directly from the building main HV/LV transformer with separate neutral and earthing point. There is a Make-Before-Break Switch(MBBS) (4P) for transferring the UPS source to the External Maintenance Bypass Source. However, if the MBBS is switched over, that would cause the external maintenance bypass neutral to be shorted to the earth point. The incoming breaker is protected by an ELR set at 10A. Will the switchover cause a trip to the ELR?

 

[waross]

If there ever was a time for this old standby, this is it.
It depends.
Another issue:
When a switch is being operated it may be at the greatest risk of failure.
If the switch fails during switching, your ELR may not operate as expected.

Bill
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Jimmy Carter