Up to around 3000v DC off a local generator IIRC (thus the dimming of
the prison lights as seen in many films is a load of old cobblers).
There was a DC v AC competition involving the public killing of an
elephant in the early days of deciding the "best" way to fry people;
prior to that Thomas Edison "perfected" his AC system by killing
numerous cats and dogs in experiments :-
http://www.ccadp.org/electricchair.htm

The local SPCA used to electrocute animals. Then they went to gassing, now
it's the needle.


--
Cheers

Roger T.
Home of the Great Eastern Railway at:-
http://www.highspeedplus.com/~rogertra/
Latitude: 48° 25' North
Longitude: 123° 21' West