CB electronic trip unit
CB electronic trip unit
(OP)
Anyone knows how to specify a power circuit breaker having electronic trip unit? a complete specification would be better.
Does Ground fault tripping is required for a minimum specification or it depends to the customer's discretion?






RE: CB electronic trip unit
LT is for overload conditions and is always necessary.
ST is for high current overloads or low level faults, and will provide a short time delay for these issues.
Inst is for short circuits, and GF is obvious.
Typically, a Main or Tie C/B would have LT, ST, and GF. You wouldn't want Inst, because this may trip along with a feeder C/B Inst, and cause a much larger outage. Per the NEC (if it applies to you), a Main C/B for a 480V (and above) system must have GF.
A feeder C/B should typically have LT, ST, Inst, and GF. This allows proper downstream protection and coordination with the upstream Tie and Main C/Bs. The NEC requires only feeder C/Bs of 1200A trip to have GF, but you'll find that specifying every C/B is typical and will help with GF coordination.
RE: CB electronic trip unit
RE: CB electronic trip unit
For normal operation, the protection runs with setpoint file 1. If switching and racking operations are going to take place, the user selects the faster setpoint file 2.
Of course, this requires a more advanced protection relay, available for a nominal fee...
old field guy
RE: CB electronic trip unit
Newer breakers can be purchased with switchable instantanteous and ground fault, so that these can be switched off if not desired for a particular breaker.
RE: CB electronic trip unit
With all due respect:
"Anyone knows how to specify a power circuit breaker having electronic trip unit? a complete specification would be better."
Sounds like you want someone else to do the job for you. Did you check with any manufacturers?
RE: CB electronic trip unit
RE: CB electronic trip unit
rbulsara, i got your point. In my case, i'm on the verge of tracking and somewhat upgrade our maintenance program for our equipments due to abscence of data and limited operating manuals, i resort to ask such absurd query. The fact, i have limited knowledge about this trip unit.
Though these equipments niether experience trip out ,eversince. I'm optimistic that this will trip out, sooner.
Guys, i'm interested on Ground fault. I recently read a document which says "GF is 20-30% of the phase setting
and it's time setting is about or at least 0.1sec." How to discriminate this setting against INST setting? Anyone can ellaborate this, please?
Definitely, I 'm talking about a low voltage Circuit Breaker: Cutler-Hammer, DS II, digitrip 510 rms.
Unfortunately, i found hard to download this stuff on-line. Unsurprisingly, i post this inquiry.
Thanks a lot, guys!
bil
RE: CB electronic trip unit
Other units actually require a separate outboard CT or sensor. These can be set at a more sensitive level, but add complexity to the installation.
Since the G/F setting is lower (MUCH lower) than any instantaneous setting, the G/F will operate for low order ground faults well before current reaches a level to operate any instantaneous element.
If the fault is high enough to operate both the G/F and the instantaneous elements, I want that fault cleared, regardless of what element takes the breaker open.
old field guy
RE: CB electronic trip unit
I am not sure you got answer to your original question. If I understood you correctly, you have to specify which functions you want in a trip unit. Essentially you need to pick one of the follwing sets, in your specification:
LI
LSI
LS
LSG
LSIG
You can also replace G with a A if you want groud fault "Alarm" only. G means it is for tripping on ground fault. There may be some other combination. LSI and LSIG are most common.
Now whether or not a ground fault proteciton is required by Code is a different issue. NEC spells out when a GFP is required. There may be other reasons to have or not have GFP. In any case you can not circumvent the code.
If you are looking for selectivity between a main and feeder breakers when a ground on a feeder occurs, you may want to have GFP in mains and all feeder breakers. Turst me this decision making takes lot of factors into account, and not possible to advise as a rule of thumb.
RE: CB electronic trip unit
Replacing a trip unit in field is usually expensive and cumbersome.
RE: CB electronic trip unit
The new line from them has "Quick Trip" settings that basically like others have stated ther are an additional set of certain settings that are activated by the flip of a switch.
If anyone is considering using a relay that has multiple/ selectable settings be sure to have some sort of alarming capability so no one forgets to turn the switch back to "normal" operation.
My 2 cents