When comparing the time-current curves of two circuit-breakers, you are likely to consider the trip times of the two devices as if they were passed through by the same current.
This consideration is true only when, between the two circuit-breakers in series, there are no other shunts, i.e. there is a single incoming and a single outgoing feeder insisting on the same node. When, on the other hand, there are several supply-side circuit-breakers that insist on the same busbar or several outgoing feeders on the load side, the currents flowing through the devices can be significantly different.
Three cases are considered:
A single circuit-breaker on the supply side of a single downstream circuit-breaker
(passed through by the same current).
- A single circuit-breaker on the supply side of several downstream circuit-breakers
(supply-side circuit- breaker passed through by a current value higher than that of the load-side circuit-breakers).
- Several circuit-breakers on the supply side and several circuit-breakers downstream