Datasheet

US Catalog | Miniature Circuit Breakers 49
Main
breaker
65 kA
CB1
10 kA
CB2
10 kA
CB3
10 kA
CB4
10 kA
35 kA or 65 kA short circuit
Selective coordination and series ratings
Selective coordination
Selective coordination is achieved when there is a short circuit
on a branch circuit breaker, the branch breaker opens and
isolates the fault, and the main breaker remains closed. The rating
is usually a value above the “stand alone” interrupting rating
of the branch breaker and the “stand alone” rating of the main
breaker.
Example:
65 kA rated main breaker
10 kA rated branch breaker
Coordination between the two breakers up to 35 kA
There can be a short circuit on the branch breaker up to 35 kA
where the branch will open (CB1) and the main breaker will
remain closed. Although the branch has a 10 kA “stand alone”
rating, both the breakers work together to limit the available
short circuit to allow the branch (CB1) to isolate the fault.
Series ratings
Series ratings are different from coordination ratings. Unlike
coordination ratings where the branch opens and the main
remains closed, a series rated combination is one where both the
branch and main breakers open and work together to isolate the
fault.
The series rating combination of two breakers is equal to the
“stand alone” interrupting value of the main breaker. This is a
result of the main breaker let-through value being lower than the
“stand alone” interrupting value of the branch breaker. During a
short circuit the main breaker will limit the energy to a level that
is below the “stand alone” value of the branch breaker.
Example:
65 kA rated main breaker
10 kA rated branch breaker
Series combination rating between the two breakers up to 65 kA
There can be a short circuit on the branch breaker up to 65
kA where the branch will open and the main breaker will open.
Although the branch breaker (CB1) has a 10 kA “stand alone”
rating the main breaker has a let-through value below 10 kA.
If there is a fault up to 65 kA on the network, the main breaker
will limit the energy to a value less than the rating of the branch
breaker (CB1). Both breakers will trip (no coordination), but the
network can safely withstand a fault of 65 kA.