MK Electric Catalogue No. 49

582 / 759

CIRCUIT PROTECTION
582
RATING SPECIFICATION
TYPE B SINGLE POLE RATING
5903s 3A
5906s 6A
5910s 10A
5916s 16A
5920s 20A
5925s 25A
5932s 32A
5940s 40A
5945s 45A
5950s 50A
TYPE C SINGLE POLE RATING
8703s 3A
8706s 6A
8710s 10A
8716s 16A
8720s 20A
8725s 25A
8732s 32A
8740s 40A
8750s 50A
FEATURES
l Meet BS EN and IEE Wiring Regulation
requirements
l Trip-free’ mechanism
l Positive contact status indicator
l Tunnel type, touch-proof, captive terminals
l Generous terminal capacity
l Can be used as single pole isolating switch
l Protective shutter
Sentry Technical
Miniature Circuit Breakers (MCBs)
Installation
Selection of the most suitable MCB should take into account the following
considerations:
1. Operating voltage and frequencies
It is possible to use the Sentry MCB on other voltages than 230/400V a.c. 50Hz, but
it should be noted that this takes the MCB outside the scope of BS EN 60898.
2. Type of load
RESISTIVE
No derating is required in the case of resistive loads.
INDUCTIVE
In the case of inductive loads from direct-on-line motors, the surge on energisation
can produce up to 5 times full load current, which may be present for several
seconds. It is therefore recommended that Type C MCBs are used for such circuits.
When using assisted start motors, the usually quoted figures are 2.5 times the full
load current, for periods generally longer than those for direct-on-line starters. It is
thus important to establish the degree of inrush current in order to select a suitable
MCB. In all instances, reference should be made to both the motor manufacturer’s
curves and MK’s circuit breaker curves in order to select the compatible miniature
circuit breaker.
CAPACITIVE
Surges on energisation, for example with discharge lighting, may well reach 25
times the rated current of the device, but only for very short duration. Type B
devices will often be adequate, but for more specialised circuits, a Type C may be
required. The lighting fitting manufacturer’s recommendations should be observed.
Description (continued)
Operating characteristics
TYPE B
The magnetic operating limits are between 3 and 5 times the current rating of the
MCB. Under these conditions the mechanism of a 10A MCB will operate between
30A and 50A in an overcurrent situation.
TYPE C
In the case of Type C MCBs, the magnetic operating limits are between 5 and 10
times the current rating of the MCB. Under these conditions the mechanism of a
10A MCB will operate between 50A and 100A in an overcurrent situation.
Type C devices are capable of supplying the majority of inductive and capacitive
loads such as motors, transformers and tungsten or fluorescent lighting.
Time/Current and Energy let through characteristics of Sentry MCBs are shown
graphically on the Time current characteristics chart (See separate document).
TYPE D
The Type D MCB is suitable for applications involving equipment generating very
high inrush currents, e.g. x-ray equipment, transmitters and computer power
supplies. The magnetic operating limits are between 10 and 50 times the current
rating of the MCB.
(For Modular Combi use only)