Driving a DMU

Effects of Jumpers Becoming Disconnected

(Compiled by Stan Acaster (Dean Forest DMU Group))

There are four jumper cables between each vehicle. They may be considered to be divided into two pairs; an outer pair Nos. 1 and 4 and an inner pair, Nos. 2 and 3.

Consider the outer pair:-

No. 1 carries the following circuits

Cars 1, 5 & 6     Engine and Air/Axle indicator lights.
All Cars     Gears 1, 2 , 3 and 4.
All Cars     Throttle 1, 2, 3 and 4.
All Cars     Start engines RIGHT side of train.
All Cars     FORWARD direction.

No. 4 carries the following circuits

Cars 2,3 and 4     Engine and Air/Axle indicator lights.
All Cars     Gears 1, 2, 3 and 4.
All Cars     Throttle 1, 2, 3 and 4.
All Cars     Start engines LEFT side of train.
All Cars     FORWARD direction.

Nos. 2 and 3 carry the following circuits

All Cars     STOP engines.
All Cars     D.S.D. Valve Control/
All Cars     Train Wire positive and negative.
All Cars     Buzzer.
All Cars     Fire Alarm.
Tachometer 1, 2 and common.

Note the duplication in cables 1 and 4 of gearbox and throttle controls, and that No. 3 is a duplicate of No. 2.

No. 1 jumper will be considered to be the left-hand one in the direction of travel and No. 4 the right-hand one.

It is immaterial as to the order of Nos. 2 and 3 because No. 3 duplicates No. 2.

DO... check that jumpers are firmly in their sockets and safety chains secured during preparation, at terminal points and during attaching and detaching operations.

Effects of No. 1 Jumper Cable Becoming Disconnected Between Any Two Power Cars

Note: The effects are apparent only for power cars in the rear of 'brake'.

No. 1 Jumper Disconnected

Referring to Table 1 of the key diagram: the engine and air/axle lights for any power car shown in this table which is in the REAR of the 'break' will go OUT.

If REVERSE is selected, all power cars in ADVANCE of the 'break' will reverse but those in the rear will remain in forward. If FORWARD is selected again all power cars will be engaged for this direction.

If the engines are NOT running and the RIGHT side start button is pressed in the driving cab, only the engines down the RIGHT side of the train which are in ADVANCE of the 'break' will respond, those in the rear will not. All engines down the LEFT side of the train will respond to the pressing of the LEFT side start button in the cab.

No. 4 Jumper Disconnected

Referring to Table 4 of the key diagram: the engine and air/axle lights for any car shown in this table which is in the rear of the 'break' will go OUT.

If REVERSE is selected all power cars will reverse.

If FORWARD is again selected all the cars in ADVANCE of the 'break' will return to FORWARD, those in the rear will remain in REVERSE.

If the engines are NOT running and the LEFT side start button is pressed in the driving cab, only the engines down the LEFT side of the train which are in advance of the 'break' will respond, those in the rear of it will not. ALL engines down the RIGHT side of the train will respond to the pressing of the RIGHT side start button in the driving cab.