System performance is guaranteed by coordination between the Merlin Gerin
circuit breaker protection and the distribution spread over the Canalis busbar
Fully coordinated distributed electrical distribution perfectly meets the requirements
of safety, service continuity, system changes and simplicity.
In the following pages, we will explain the advantages of the Schneider Electric
system and Merlin Gerin circuit breaker protection, as well as the selection guide
tables for coordination between the Merlin Gerin circuit breakers and the Canalis
The use of Merlin Gerin circuit breakers provides:
protection against overloads and short-circuits;
coordination between the protective devices and the Canalis busbar trunking:
full discrimination from 1 to 6300 A between all the circuit breakers of the Merlin
- reinforcement of the small and medium power busbar trunking short-circuit
protective devices. This enables all short-circuit levels to be covered,
- protection of tap-offs using standard circuit breakers: this is achieved whatever
the position of the tap-off unit on the Canalis busbar trunking;
the use of standard circuit breakers makes for simpler design whilst respecting a
high level of dependability;
fault location is quick and easy;
resetting is easy once the fault has been cleared by the site operator.
Protection of busbar trunking against
Adequacy between circuit breaker
ratings and busbar trunking
In order to take into consideration thermal overload protection of busbar trunking,
the different technologies of the protection switchgear and the maximum overload
operating currents must be considered.
By design, the thermal adjustment of a circuit breaker is more accurate.
Inc = Ib x k1 x k2,
Ib : current rating,
Inc : allowable busbar trunking current,
k1 : temperature derating coefficient,
k2 : derating coefficient linked to the type of switchgear:
- fuse k2 = 1.1
- circuit breaker k2 = 1.
Iz = Ib x k1.
In = I standardised fuse or circuit breaker.
For a current rating Ib = 1900 A in an ambient temperature of 35°C:
Inc = Ib x k1 x k2 = 1900 x 1 x 1.1 = 2090 A
The correct choice of busbar trunking is the KTA25 (Inc = 2500 A),
circuit breaker protection:
Inc = Ib x k1 x k2 = 1900 x 1 x 1 = 1900 A
The correct choice of busbar trunking is the KTA20 (Inc = 2000 A),
A difference of 20 % in the measurement of operating currents results in an over-
rating of the busbar trunking of 10 % if it is protected by fuses.
Calibration of thermal asymptotes:
the distribution fuse is calibrated to operate for overloads of between 1.25 and
1.6 times its nominal current (In fuse),
the circuit breaker is calibrated to operate for overloads of between 1.05 and
1.3 times (1.2 for circuit breakers with electronic protection) its setting current (Ir
which is a function of circuit breaker In).
Maximum operating current:
the maximum limit for this current is set by installation standards (IEC 364,
NFC 15-100, etc) at 1.45 times the allowable current of the busbar trunking.