K9AE31000
10
Schneider Eletric
Design guide
Design guide
Coordination
Protection against short-circuits
Busbar trunking characteristics
The busbar trunking must meet all of the rules detailed in IEC 60439.1 and
IEC 60439.2.
The sizing of busbar trunking for short-circuits is determined by the following
characteristics:
the allowable rated peak current Ipk (kÂ).
This characteristic represents the busbar trunking's instantaneous
electrodynamic withstand limits. The peak current value is often the most restrictive
instantaneous characteristic for the protective device,
The maximum short-time withstand rms current Icw (kArms / s).
This characteristic represents the allowable temperature rise limit of the
conductors during a given time period (0.1 to 1s),
The thermal stress in A
2
s.
This characteristic represents the instantaneous thermal stress withstand of the
busbar trunking. In general, if the short-circuit generates fault conditions compatible
with the first two characteristics, this constraint is "automatically satisfied".
b
b
b
b
b
b
Circuit breaker characteristics
The circuit breaker must satisfy the requirements of product construction standards
(IEC 60947-2, etc) and installation standards (IEC 60364 or those in force in the
country concerned), i.e. have a breaking capacity Icu
(1)
greater than the prospective
short-circuit current Isc at the point where it is installed.
(1) Installation standard IEC 60364 and construction standards specify the breaking capacity of
a circuit breaker as being:
- the ultimate breaking capacity, Icu, if it is not coordinated with an upstream protective device,
- the reinforced breaking capacity (cascading) if there is coordination with the upstream
protective device.
Circuit breaker / busbar trunking system
characteristics
When the busbar trunking is directly protected, the circuit breaker must be chosen
as follows:
Icu of the circuit breaker u prospective Isc at point A,
I peak of the busbar trunking u prospective asymmetrical or limited Isc at point A,
busbar trunking thermal withstand Icw u thermal stress through the busbar
trunking.
When the busbar trunking is protected downstream of a cable, the circuit breaker
must be chosen as follows:
Icu of the circuit breaker u prospective Isc at point A,
I peak of the busbar trunking u prospective asymmetrical or limited Isc at point B,
busbar trunking thermal withstand Icw u thermal stress through the busbar
trunking.
b
b
b
b
b
b
Canalis KTA
DD210986
DD210987