As of 2007, ET40 locomotives work mostly for Bydgoszcz engine shed, but in 2000 several units were sent to Wrocław in order to serve on the highland Wrocław-Jelenia Góra line, where they are intended to replace ET21 locomotives.
ET40 is a Bo-Bo+Bo-Bo locomotive, meaning it is an articulated engine with two cabs fixed to the frames placed on two bogies. Each bogie has two driving axles and each axle is propelled separately by 7AL-484ZT traction engine with 510 kW constant power. Its parameters allow the machine to pull freight trains of approximately 4,000 t. weight.
Crew compartments provide convenient driving of the machine in both directions. Entrance is possible through the doors on both sides of the locomotive. Crew compartments are heated with a fan powered electrically; windscreens are equipped with de-freezers and wipers. On the rear side of the crew section a locker for clothes and electric devices is mounted. Entry to the mechanical compartment is possible through two doors. The right one leads to high voltage section, whilst the left provide access to the other crew compartment through a corridor running along the whole locomotive.
The mechanical compartment is divided into three parts. Auxiliary fixtures, like traction motors cooling systems, resistors and main compressor are located in the rear part of the section. Refrigerator, washbasin and cooker occupied the front part of the corridor.
The ET40 locomotive is equipped with an electro-pneumatic device to level otherwise unequal load on the track. The machine is equipped with two pneumatic brakes - one automatic Oerlikon and additionally, braking only one section. Locomotives numbered from 01 to 30 had one pantograph per section, whilst those numbered from 31 to 60 had two pantographs per section. Traction motors are connected with a series connection with voltage for each motor being 1500 V. They are cooled by two fans (one fan for two engines) with the air supplied by two intakes in the roof of the locomotive. Air for braking systems is provided by two compressors (one for each section) with nominal power of 140 m3/h.