Emax Low voltage air circuit-breakers - ABB Download Center

Installation in switchgearChoosing the type of circuit-breakerNumber of polesThe choice of the number of poles for circuit-breakers that simultaneouslyprovide switching, protection and isolation functionsin three-phase installations depends on the type of electricalsystem (TT, TN-S, TN-C, IT) and the type of user or, moregenerally, whether it features a distributed or non-distributedneutral.Three-pole circuit breakersFour-pole circuit breakersThree-pole circuit breakerswith external neutral3For TN-C systems (the neutralcannot be interrupted because italso acts as the protectionconductor).For users that do not use theneutral (e.g.: asynchronous motors)and, for systems with undistributedneutral in general.In all other instances, withexceptions for the IT system(see CEI 64-8/473.3.2.2Standards).Current transformers can beinstalled on the external neutralof five-wire systems (TN-S) with3-pole circuit-breakers.Fixed or withdrawable versionThe fixed version of the circuit-breaker is more compact in size than the withdrawable version. Itis recommended for installations that can tolerate service interruptions in the event of faults orprogrammed maintenance.The withdrawable version of the circuit-breaker is recommended for:– applications that can only tolerate brief interruptions due to faults or programmed maintenance;– dual lines, one of which is a standby for the other, with a single circuit-breaker for each pair.1SDC200083F0001ABB SACE 3/3