Traction Current: Alive or Dead? (1989)

Very interesting.

My recollection is that those old SCDs were withdrawn in the 1980s. However, that film appears to be from the 1980s so I guess the SCDs lasted until at least the middle of the decade.

I noted that the commentator suggested that SCDs were only found on trains, that is simply not true! Engineering had their own SCDs for use when taking out Possessions, for staff training, for Traction Current CB Trip testing etc.

Ah, ok. I was probably thinking of the current testing device, that the ERU use to test that current has been discharged when they go onto the track, as seen in the "Emergency Response" episode of "The Tube"

I guess they were still a part of on board train equipment then but we had the new SCDs on engineering in the early 1980s and the old heavy lumps disappeared rather quickly. My recollection is that the new type were replaced rather quickly and more than once by modified varieties for various issues such as poor or inadequate insulation, poor clamping or magnetic adhesion to rails etc.

There were definite safety issues with the earliest versions of the new types. Tripping traction current using the SCD was part of routine electrical maintenance testing and it was not unknown for two men to be required to place and hold the new light SCDs until the substation CBs tripped. Sometimes two men were not enough as the juice 'threw' the SCD and the men according to some of my electrical colleagues.

You need to do the self test before putting it on the current rails.