Pre-start warning system and machine incorporating such system

A pre-start warning system for supplying electrical energy at an intrinsically safe level to an electrical machine, said system comprising two low speed generators mechanically coupled together, a drive shaft to rotate said generators and the mechanical input at said drive shaft producing a separate, isolated, electrical output at each of said generators, an intrinsically safe barrier means and first and second circuits, a pre-start warning device incorporated in said first circuit, said output from a first one of said generators being fed to said intrinsically safe barrier means, whereby an intrinsically safe power supply is made available to power said first circuit and said pre-start warning device thereof, said output from a second one of said generators being fed to said second circuit which is a non-intrinsically safe circuit, and said barrier means incorporating an opto-coupled isolator constituted by a fibre-optic link between said intrinsically safe circuit and said non-intrinsically safe circuit, to achieve electrical and physical segretation of said first and second circuits, and said first circuit being a control and/or monitor circuit incorporating, as said pre-start warning device, an audible sounder, with an acoustic monitor to monitor the output of said sounder for a predetermined time period, after which period said control and/or monitor circuit is able to energise said intrinsically safe barrier means.