Short circuiting bars / devices

Obviously standard equipment now for many years on all stock - but the excellent Railways archive website has the full December 1945 Northwood collision on it - triple collision in thick fog and states that one of the reasons why the local fire brigade was unwilling to put out the fire caused by arcing -was that traction current was still on. All trains involved - one loco hauled Aylesbury train and 2 slam door sets did not carry SCD equipment - and contact with the substation was necessary.

Any old hands around who can confirm this state of affairs on "surface" stock and when was the equipment normally carried.?

I believe from the earliest days on the Southern and LMS electrics that the equipment was always part of the emergency equipment on DC electrics.