Originally constructed in 1893 as the Engine House, it was fitted originally with two 90hp Galloway vertical compound engines (supplied from the boilers in the house alongside), which were equipped with two 9ft diameter flywheels. These, via leather link belts, supplied two Mather and Platt dynamo generators, with two switchboards and associated switchgear, also by Mather and Platt.
In 1894, a third compound engine was installed to complement the original two alonsgside a third dynamo of Hopkinson construction with additional switchgear following. Following the decision by the company to offer electric power as a public supply, an additional Mather and Platt alternator was installed at the west end, with a Bellis/Mather and Platt example following in 1896. In 1898, the switchgear was once again replaced and mounted on a elevated area on the north wall.
The building was rebuilt into the Machine Shop in 1904, following the decision to generate AC power at Laxey Power Station to supply this section entirely. The switchboard and rotary equipment were moved here from the boiler house. The 1893/94 Galloway engines and Mather and Platt/Hopkinson dynamos were sold off, and the 1896 Bellis/Mather and Platt set split; the 75hp Bellis engine replaced by a 75hp Witting, Eborall and Co motor (the Bellis original was sold). The rotary converters were moved, one moving to Laxey Power Station, two to Ballaglass Power Station (one later fitted at Snaefell), with the others to a new substation building at Groudle. New switchgear from Witting, Eborall and Co was also installed.
Following the discontinuing of publicly supplied electric power, the Witting, Eborall and Co/Mather and Platt equipment was removed between 1931 and 1933. The elevated equipment was replaced in 1934 by Mercury Arc Rectifiers, which were in turn replaced in 1980 by a solid state built ground floor installation. The former 1934 equipment is however able to be viewed as part of the Derby Castle Car Shed and Workshop guided tours, held usually in the Easter and July event periods.