As for the British DC system I think paul UK could give more detail but as far as I know they used BS546 style 3-pin polorised plugs and a 2-pin ungrounded and unpolarised plug
The 200/400 to 250/500V DC systems, aw found in the old sections of some British towns were generally used with conventional BS546 plugs. Keep in mind that as far as residential servive was concerned, houses generally took only a 2-wire 200 to 250V service, with half the houses having a positive "live" and half having a negative "live" wire.
I think what Hutch is querying though is what was used in the very early
days when some districts had a 110/220V DC supply. I'm not sure how far back our round-pin plug specifications go -- They may have been used on those early 110V systems.
similar to Europlugs but with shorter fatter pins. (not unlike the current UK shaver plug)
Exactly the same dimensions as the current shaver plug in fact, although without the shielded pins which are common on the latter nowadays.
I am also not 100% sure when they standardised on 240V 50Hz or what other systems were around.
I'm not sure when the decision was made to standardize, but the conversion program took many years to complete. Full standardization at 240V was finished only in the early 1970s, and up until that time radio, TV, and other more sensitive equipment was fitted with a voltage range adjustment.
Prior to standardization the declared nominal voltages were anything in the range of 200 to 250V, usually in 10V steps. That's why most old wiring devices were rated for 250V maximum.
[This message has been edited by pauluk (edited 12-30-2003).]