"IAC is ac traction with dc traction motors," Mr Tom Chenoweth, NRE's director of electrical engineering, told delegates at the conference organised by the Locomotive Maintenance Officers Association (LMOA) at Railway Interchange. "IAC will produce a 33-35% increase in tractive effort. The tractive effort surpasses all conventional dc locomotives, with adhesion capabilities approaching the latest ac traction locomotives on the market."

An IAC conversion is designed to be minimally invasive as most of the locomotive's existing equipment is retained. It involves installing NRE's NForce microprocessor control system and choppers. One chopper is fitted per axle for maximum wheel creep performance. Wheel slip correction is instantaneous with a reduction in power only to the wheels that slip.

Adhesion is optimised without the use of traction motor speed probes, although if probes are available they can be used to detect locked axles. IAC provides individual motor cut-out, and if one motor fails 85% of tractive effort is maintained.

"In low-speed service, such as yard switching or in a hump yard where tractive effort is key, more work can done more quickly and with less power," Chenoweth told delegates.