Overhead Line Steady Current testing

During the late 90s and early 2000 various test trains were operated over electrified lines in order to give a steady current load to enable the effect of the return traction currents on the infrastructure to be assessed.

Two class 90 locos were usually utilised but the early tests were conducted with class 91 locos.

The methodology was based on the ‘speed set’ controls fitted to these locomotives, which allowed power to be applied to reach the set speed and automatically applied the rheostatic brake should that speed be exceeded.

The two locos were coupled together mechanically but not electrically. With a driver in the leading cab of each loco the rearmost speed control was set to 10 mile/h. The locos would then move off together and after the speed exceeded 10 mile/h the rearmost loco would enter its braking mode and apply rheostatic brake thereby presenting a ‘load’ to the leading locomotive. Running at a pre-determined speed of approx 40 mile/h allowed the leading loco to draw around 100A from the overhead line.

It was dependant upon a reasonably level track and a test site with sufficient distance to maintain 40 mile/h for a while. We did these tests in a T (iii) possession and over anything up to twenty miles. We had an open line to all parties undertaking the lineside monitoring and everything was synchronised. Various lineside points of interest were listed with their location (miles/chains) such that as the train proceeded the test engineer on board could relay to the testers in the sub stations when the train passed these places - booster transformers, mid-point anchors etc. Biggest problem was that the tests were usually done at night so spotting details like this was difficult.  To help us see in the dark we had a couple of portable headlights which we mounted on the front lamp brackets of the leading loco.. We also had a powerful hand held torch in the cab - occasionally the local testers would place reflective tape on certain structures before the job was carried out and these were a boon.

Amongst the sites where testing was undertaken were the Heathrow Express lines - (a class 90 at Terminal 4!), Liverpool Street to Southend, the ECML near Stevenage, the Hertford Loop, Port Glasgow to Wemyss Bay, WCML in Scotland, Newcastle Tyne Yard area. More recently the Manchester South re-signalling scheme and the Crewe to Kidsgrove electrification project were added to the list as were the east side lines at St Pancras International now used by South East Trains .

Click on the picture for a bigger image - pictures are the author's unless otherwise credited

Down Slow Crewe

Prior to undertaking the first tests the principal was trialled at Winsford, near Crewe on the WCML. Here 90147 and an unidentified sister loco is pictured on the Down Slow line sometime in 1997

Chris Ward

Stockley Bridge

Pictured at the temporary station of Stockley Bridge which was erected as part of the Heathrow Express railway - mid-1997. The station was built due to the delays in the completion of the tunnelling work, following the partial collapse during construction.

Out of the picture shuttle buses ran from the station to the Heathrow Terminals. On the right of the picture you can see construction work on the tunnel entrance which was taking place in a cutting behind the locomotive.

Chris Ward

Stockley Bridge

Looking in the opposite direction the pair of class 90 locos which formed the test train are pictured in the platform at Stockley Bridge.


The Class 90's were undertaking 'Loadbank tests' to confirm the immunisation of the signal and telecoms on the route and the adjacent London Underground lines around Paddington. Further tests were undertaken once the tunnels and Terminal stations were opened which included OHLE Test Car MENTOR and the once in a lifetime sight of a Class 90/47/90 combination into Heathrow Terminal 4!

Chris Ward

A summer night at Shenfield in 1998 with two Freightliner class 90's. Note the extra headlights on the lamp brackets to assist with identification of aspects of the infrastructure via reflective markers at pre-determined locations on the OHLE masts

4 class 90's & a class 66

A mega train of four class 90's and a class 67 was put together for a Christmas Day 2001 loadbank test at Corey's Mill, near Stevenage and is pictured at Sandy with 90141 carrying a special headboard. The diesel locomotive was for traction when the OHLE current was not available.


Cheadle Hulme

Pictured early on a summer morning another load bank test train sits in Cheadle Hulme Up Wilmslow platform in July 2002.


A bit dark but this is Newcastle Central station on a June 2003 night.

Manchester Pic

90041 in company with 90045 pictured in Manchester Piccadilly station around 02.00 on a June 2004 morning

St Pancras East

90050 is one of a pair of Class 90's in the new St Pancras East station during its OHLE commissioning on 23rd August 2004

Chris Ward

Come here often?

Face to face in St Pancras

Chris Ward

In mid 2004 it was announced that Network Rail were to convert two Class 86 locomotives into mobile loadbank locomotives, the work was subsequently carried out at Barrow Hill.

Both in full Network Rail yellow with logos, they were renumbered into the 86/9 sub series having had the number 86901 (previously 86253) and 86902 (previously 86210) and are currently based at either at Rugby if working on the West Coast Main Line or York if on the ECML. Heavily modified for their role and with additional equipment to enable fine adjustment to the level of current collection, they spelled the end for our involvement in this kind of work.

Loadbank locos

The two modified class 86 locos acquired by Network Rail for loadbank testing pictured at York between duties on 17th February 2007

The work which we undertook with the class 90 (and class 91) locomotives fulfilled a requirement for this sort of operation for nearly nine years, but all good things ...................

However the 2 x class 86 conversions are no longer in use.

86901 was sent to Booths, Rotherham in May 2014 and was still on site in September 2015. However it was rescued and was recently (Feb 2018) seen stored at Crewe Basford Hall, but in June 2018 it was on the move having been stripped completely to a bare bodyshell - presumably on the way to the scrappers

86902 was also sent to Booths, Rotherham in May 2014 and was scrapped in November 2017


R&DD had previously converted a class 84 locomotive (84009) for use as a loadbank locomotive in 1978 and re-numbered ADB968021  -  but I have no information about its use.
R&DD's loadbank locomotive ADB968021 hauled by 31405 appears to be undertaking a steady current test at Grantham on the newly installed OHLE whilst 156417 pauses at the platform - Saturday 2nd  July 1988

Brian Addis

The locomotive is pictured here at Crewe ETD on 1st December 1991

Russ Thompson



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