brian john
Senior Member
- Location
- Leesburg, VA
Actually without further input from the OP, IMO all we can do is make SWAGs.
7 Breakers tripping
- Thread starter Natfuelbilll
- Start date
- Status
Actually without further input from the OP, IMO all we can do is make SWAGs.
rcwilson
Senior Member
- Location
- Redmond, WA
Sketchy data, but here's a guess. 3000' of 13.8 kV cable with shields bonded at both ends and tied to ground will tie the remote utility system and the local grounding system together.
Assume the circuits that are tripping all have ground fault protection and have some anomaly in the way they are wired - poor neutral to ground connection, poor grounding connection, multiple neutral to ground connections, ground wire through GF CT, etc. (Heat trace circuits have GF per code. Many 480V heating elements also have GF. Don't know how your 277V lighting gets in this category).
Assume that the utiilty experiences a 13.8 kV fault somewhere else on their system and the return fault current flows in the lower impedance path of the cable shields and the new facility ground system creating ground currents in unexpected paths. The ground currents flow through the GF CT's causing breaker trips.
This did happen at one of my old facilities. No faults occurred in our plant but a nearby utility line fault current liked our copper paths a lot more than the earth return. The currents tripped multiple miswired GF systems that had operated OK for years.
Assume the circuits that are tripping all have ground fault protection and have some anomaly in the way they are wired - poor neutral to ground connection, poor grounding connection, multiple neutral to ground connections, ground wire through GF CT, etc. (Heat trace circuits have GF per code. Many 480V heating elements also have GF. Don't know how your 277V lighting gets in this category).
Assume that the utiilty experiences a 13.8 kV fault somewhere else on their system and the return fault current flows in the lower impedance path of the cable shields and the new facility ground system creating ground currents in unexpected paths. The ground currents flow through the GF CT's causing breaker trips.
This did happen at one of my old facilities. No faults occurred in our plant but a nearby utility line fault current liked our copper paths a lot more than the earth return. The currents tripped multiple miswired GF systems that had operated OK for years.
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
RCWilson...
Bonding shields, if to ground, at both ends will probably lead to misoperation of ground-fault relay, if zero-sequence type!
Regards, Phil Corso
Bonding shields, if to ground, at both ends will probably lead to misoperation of ground-fault relay, if zero-sequence type!
Regards, Phil Corso
rcwilson
Senior Member
- Location
- Redmond, WA
Phil - That's what I learned the hard way 35 years ago. Shield ground wires must be routed correctly back through ZS CT's.
Maybe the OP has some green wires going through ZS CT's or creating unusual neutral to ground bonds that fool the GF breakers.
Or maybe he just has bad luck, or a voltage surge, orelectrical noise affecting breakers, or disgruntled electricians throwing breakers, or inaccurate reporting of what happened when. I've had all of those scenarios trip loads and cause much confusion during investigation.
north star
Senior Member
- Location
- inside Area 51
$ $
I'd be interested to hear back from the OP and find out what
the nvestigation actually revealed as to cause or causes....Looks
like it could be from a number of plausible conditions.
Please update us **Natfuelbill** !
$ $
I'd be interested to hear back from the OP and find out what
the nvestigation actually revealed as to cause or causes....Looks
like it could be from a number of plausible conditions.
Please update us **Natfuelbill** !
$ $
- Status