Long Feeder Cables + Switchgear Line Side Protection

[mbk2k3]

hey folks,

i have a 2000ft cable that feeds a 4.16kV switchgear lineup. the cable has a 1200A breaker at the source end, so it will protect the cable adequately.

my question is this: does my 4.16kV switchgear lineup require a protection device on the line side (breaker/fuse)? are there any references to NEC/CEC that may provide a guideline?
client is suggesting using a load break switch only.

the reason i ask is because i figure the 1200A breaker will do an adequate job of protecting the cable, but what if there is a fault at the switchgear. wouldn't you want a fuse/breaker on the line side of the switchgear to quickly clear any faults and prevent damage to the cable?

 

[LionelHutz]

Why would a fault in the switchgear damage the cable if the upstream breaker is set to protect the cable?

Why couldn't you come up with settings for the upstream breaker that protects both the cables and switchgear?

 

[krisys]

As long as the upstream breaker is coordinated (graded) with the switchgear outgoing breakers, technically the switchgear incomer can be a load break disconnector.

Now a days, breaker panel and disconnector panel costs may not be substantially different. You should go for breaker. If you don't want to provide protection, fine.

 

[mbk2k3]

i guess what i meant was, wouldn't you rather have a line side protection device on the switchgear to quickly clear any bus faults on the gear?

in my mind, if i wait for the upstream breaker to operate, won't it take slightly longer? longer clearing times = higher incident energies for arc flash?

 

[unclebob]

The only good reason to make the switchgear breaker more sensitive than the upstream breaker is to save a 2000 ft walk to the guy who will have to reset the power, if a fault occurred at the switchgear. On a protection coordination point of vue, both breakers open the same circuit. They may have the same amp rating and possibly the same settings.

 

[LionelHutz]

The current is the same everywhere in the circuit when a fault occurs. Put the same protection setup at both ends of the supply cables and they will both trip in the same time.

 

[jghrist]

Having a breaker at the switchgear will allow you to use fast bus protection like bus differential or zone selective interlock. This could significantly reduce arc incident energy.