4m300-v01-1.pdf
The Test Block type 4M300 comprises fourteen test circuits, each connected to a separate pair of rear terminals. During normal operation, each pair is connected by a circuit-shorting link. For testing, the front cover is removed; on the 4M300-B model the Isolation Plug is withdrawn, interrupting the circuit between terminals 13 and 14. Routing the main DC supply through this circuit prevents inadvertent tripping during tests. Inserting the 4M320 Test Plug isolates the live-side from the equipment-side circuits. Its 28 finger-safe 4mm sockets are numbered to match the rear terminals and colour coded black (equipment side) and yellow (live side).