I'm building my own PCB lightbox( for the ignorant- I draw a circuit on a film, expose a PCB with light sensitive film using the UV from box/ develop as for a photo negative  ,then etch .I've got all the bits and circuit diagram, but notice on the RS schematic that there's a "C" across the L & N supply- any ideas ?

Power surge capacitor? 

Have you got the diagram? 

A power surge cap (or filter) would probably also have an earth connection - a cap across just the Line and Neutral will probably be for power-factor correction. 

Both replies correspond with my ideas of it's use. Personally, I can't see why it's there, and have never seen one on any Fluorescent lamps I've seen, so I'll suck it and see.

58 minutes ago, VWD said:

Both replies correspond with my ideas of it's use. Personally, I can't see why it's there, and have never seen one on any Fluorescent lamps I've seen, so I'll suck it and see.

I haven't been into many fluorescent light fittings but I know for a fact the one in my garage does as I moved it the other day.

 

TWM- I'd never really noticed. But another source confirms it's PF. I’m on the last stages of my light box (for PCB ) and I noticed one in the circuit. My worry was that the cap was for additional noise suppression( fluorescent fittings give off a lot of RF noise) and someone the same phase could get a lot of mains born noise down the cabling. ( i.e. -every fourth house in the road will be on the same phase as I'm on)