Circuit Breakers

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brian john

brian john

Senior Member
Location
Leesburg, VA
jrannis is correct, what size is the lower CB? are they the same style?


In-A-Gadda-Da-Vida
A local radio station use to plpay In-A-Gadda-Da-Vida every Saturday at 6:00 PM
I-Tunes does not have the full version.
 
Buck Parrish

Buck Parrish

Senior Member
Location
NC & IN
glennyamada said:
What would cause a 3 phase 100a breaker to trip before the branch circuit
breaker which is rated at a lower amps?
Click to expand...



(1)Lightning, (2)several circuits together pulling less then their load but more then 100 a. (3) short circuit (4) bad breaker (5) burned or corroded bus bar (6) If the power goes off then on quickly, Every thing starting at the same time. (7) etc...
 
G

glennyamada

Member
Location
HI
Circuit Breakers

The load center consist of many single phase 20a and 50a double pole breakers. I was told the it could be the ACI rating of the main breaker, might be lower the the ones in the load center.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
glennyamada said:
The load center consist of many single phase 20a and 50a double pole breakers. I was told the it could be the ACI rating of the main breaker, might be lower the the ones in the load center.
Click to expand...
.


No, No. NO.

The AIC rating of a molded case breaker has nothing to do with its trip characteristics. Another urban myth.
 
N

nakulak

Senior Member
brian john said:
jrannis is correct, what size is the lower CB? are they the same style?


In-A-Gadda-Da-Vida
A local radio station use to plpay In-A-Gadda-Da-Vida every Saturday at 6:00 PM
I-Tunes does not have the full version.
Click to expand...

you lost the album ?
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
glennyamada said:
What would cause a 3 phase 100a breaker to trip before the branch circuit
breaker which is rated at a lower amps?
Click to expand...
\

Plan and simple, a short circuit can cause that.

A single pole 20 amp breaker can have a lower, equal or higher instantaneous trip rating then the 100 amp breaker.

I have had a short circuit on a 30 amp breaker take out a 400 amp feeder, both breakers tripped at the same time.
 
jrannis

jrannis

Senior Member
Location
Fort Lauderdale/ Miami
brian john said:
jrannis is correct, what size is the lower CB? are they the same style?


In-A-Gadda-Da-Vida
A local radio station use to plpay In-A-Gadda-Da-Vida every Saturday at 6:00 PM
I-Tunes does not have the full version.
Click to expand...

Its not that common to find the 17 minute version
 
cschmid

cschmid

Senior Member
Location
Northern cold country
oh man now I am listening to In-A-Gadda-Da-Vida is that mandatory for the coordination issue we are discussing...I had to change over to the live version..

so if you have a true coordination issue every-time you short a circuit on that phase you should blow the main..

This problem also costs you cash as the meter does not measure the average usage it measure the highest usage so if you have one leg drawing more you pay more..that is just another coordination advantage or disadvantage..:D
 
G

glennyamada

Member
Location
HI
Circuit Breakers

Troubleshoot yesterday and found that only the 100a 3 phase breaker is tripping. The breakers in the load center is not. I think it might be the feeder cable from the main to the load center. Could be insulation break down??
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Have you taken ampacity readings on the feeder?

If it is not a short circuit in a branch circuit the feeder may just be overloaded.
 
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