Class 316 has been allocated to two distinct prototype 25kV AC electric multiple units, used to to test new traction equipment in the early 1990s.

316999

The first unit, 316999, was the 'Networker' test unit in its AC overhead electric configuration. For more details, see Class 457 (its classification when in DC third rail electric configuration). The unit formation was:

Unit No.  DMSO    TSO     TSO     DMSO
316999    67300 + 67401 + 71246 + 67301

316997

The second unit, 316997, was made up of three carriages from a former Class 307 unit, 307118. It was converted to test the 'Holec' traction equipment that was later used to power the Class 323 units. Once the tests were complete, the unit was withdrawn, and two of the carriages have now been scrapped.

The unit formation was:

977708 (ex. 75018) + 977709 (ex. 61018) + 977710 (ex. 75118)