recently testing emerg gen system we shut down power in mdb to simulate power failure to start gen. the sequence we used was to open mdb 2 switch , mdb 1 sw , then main, noticing some arcing and sparking . when this occured it took out 3 fuses at utility ( incoming which is 15 kv) and 2 fuses in main sw gear? the gen worked fine . what could have caused this ? this test was performed a week earlier without any problems ? also what is procedure to drain off fuses in gear before working on it?
utility backfeeding?
- Thread starter BENNET
- Start date
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ramsy
Roger Ruhle dba NoFixNoPay
- Location
- LA basin, CA
- Occupation
- Service Electrician 2020 NEC
Some switches should not be opened while energized. If motor loads are not opened from their controllers, inductive kickback can arc across other disconnects. Same thing with capacitor banks, and bypassing ATS's.
Non orderly shut downs can cause damage. Where is the shutdown procedure and was the checklist followed in the same order as prior shut downs?
Was their any dust or fumes noticed that day. Is it possible the area is not a classified location, the environment has changed, and the disconnects were contaminated with dust.
Contractors have also put rebuilt / refurbished and unreliable breakers in new installations.
Non orderly shut downs can cause damage. Where is the shutdown procedure and was the checklist followed in the same order as prior shut downs?
Was their any dust or fumes noticed that day. Is it possible the area is not a classified location, the environment has changed, and the disconnects were contaminated with dust.
Contractors have also put rebuilt / refurbished and unreliable breakers in new installations.
Last edited:
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
Would need a better idea on what the operating loads were on system, and more details on the switches and there ratings.
As Roger pointed out, there are many switches that are not designed to be opended under load. The are no-load switches designed specifcally for disconnection after power has been removed upstream. Just becasue it has a handle, a loadbreak switch it does not make!
This could have caused phase to phase flashover, which looked like a phase to phase fault in the fuses. Your lucky nothing blew. (as in blew up and killed anybody)
As Roger pointed out, there are many switches that are not designed to be opended under load. The are no-load switches designed specifcally for disconnection after power has been removed upstream. Just becasue it has a handle, a loadbreak switch it does not make!
This could have caused phase to phase flashover, which looked like a phase to phase fault in the fuses. Your lucky nothing blew. (as in blew up and killed anybody)
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