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The unit made years ago by a Cheshire firm had a low current limit, can't remember the figures, but seem to remember once the power used exceeded around 10 amp it auto switched to direct connection. It was designed to give around 220 volt output, i.e. Europe voltage at that time, came out I seem to remember in the 80's and were tested down South to show how they saved power, which to be fair in the 80's likely they did, but the figures did not match theory.
So if you take for example a kettle, in theory the faster it is boiled the less heat is lost to atmosphere so cheaper it is to boil the water, so and where heat is not lost to atmosphere then it makes no difference if you use 2.5 kW or 3 kW as the 2.5 kW will run for longer.
So there were in real terms two devices which would benefit from reduced voltage, one was the old type power supply, the other the old type fluorescent light control gear, both which are rarely used today.
Because the auto transformer was not rated at 100A if the control gear fails and does not auto switch out the auto transformer once the current draw rises then they present a very real fire risk, so I would recommend removal. The ones that I found in the past were not as @bernardgreen shows, they used auto transformers, and it switched taping very like an auto transformer motor starter.
I think the company has now gone, it was at Capenhurst near Ellesmere Port, I never understood why tested so far away from where made? Maybe some one else has now copied their idea, but today pointless.
So if you take for example a kettle, in theory the faster it is boiled the less heat is lost to atmosphere so cheaper it is to boil the water, so and where heat is not lost to atmosphere then it makes no difference if you use 2.5 kW or 3 kW as the 2.5 kW will run for longer.
So there were in real terms two devices which would benefit from reduced voltage, one was the old type power supply, the other the old type fluorescent light control gear, both which are rarely used today.
Because the auto transformer was not rated at 100A if the control gear fails and does not auto switch out the auto transformer once the current draw rises then they present a very real fire risk, so I would recommend removal. The ones that I found in the past were not as @bernardgreen shows, they used auto transformers, and it switched taping very like an auto transformer motor starter.
I think the company has now gone, it was at Capenhurst near Ellesmere Port, I never understood why tested so far away from where made? Maybe some one else has now copied their idea, but today pointless.