.The 1928 situation:

• No national grid or supply standard. (Cent. Elec. Board only just formed in 1926).
• Local authorities and large industrial concerns set their own standards and generated power for local distribution. London had over a dozen different voltages and several different frequencies.
• Domestic dilemma of the 1920’s; buy an expensive vacuum cleaner but a later move to a different district and it might be useless.

MWB installed its own generation plant and chose an output of 200 volts D.C. - enough to avoid medium distance distribution losses yet safe for general use. Ideal for motors used for driving oil and drainage pumps as well as lighting.
The equipment is typical for its time, open contact knife switches, with slate, rubber and paper insulation.

In case their central supply failed, the MWB had a policy to ensure that each building was self-sufficient. The Engine house was provided with a water turbine driven 50 kW dynamo, sufficient power to allow the steam engines to function with essential lighting, oil and drainage.

A.C. voltages from the national grid spread in 1940/50s. The supply was more economic and reliable than local ones. Users of D.C. like the MWB adopted ways of converting the readily available grid supply.

The popular method was transformation of the A.C. voltage then rectification using the mercury-arc system. The electrical system functioned until closure in 1980. The original mercury-arc unit was vandalised and scrapped.

In May 1997 the Royal Opera House, Covent Garden closed for re-furbishment. The management gave us their redundant 50 kW mercury-arc rectifier; still warm from recent use! Now installed next to our restored D.C. switch panel and it will be set to work when effort is available meanwhile, we use a modern 10 kW solid state unit with NiCad battery back up.

House lights have been replaced with high efficiency lamps that provide much more light for our visitors but the new fittings are very similar in appearance to the original ones. The gallery lights have been rewired and also serve as emergency lighting.