What lubrication for Variac/Auto Transformer?

[Shock]

Is there any preferred way to clean and lubricate the windings on a Variac?
What do the manufacturers put on, anything?

The lubricant would have to be non conductive and safe for around 300v.

[Andy Watson]

Carbon - i.e. the graphite brush, should be a good-enough lubricant on its own. But the carbon dust is conductive - so keep it clean.

[SeanB]

Clean the top track with some cloth and IPA, and then simply wipe the moving contact back and forth 4 or 5 times then use the dry cloth again to polish off the small amount of black dust. That will keep the track bright and clean. If it is dull and oxidised use a pencil eraser ( the white soft one) to rub gently till shiny. Careful though, this does wear the wire there thinner, so only do it as a last resort.

[Shock]

I measured and it was very intermittent on ohms. I thought about using an eraser but noticed while I was probing it was hard even to scrape any of the build up off.

I ended up cleaning it well with IPA first and used some 800 wet and dry sand paper (dry). Took a few wipes got most of it off, then used IPA and a clean rag. I also leveled the brush as it was a pitted.

When mounting the brush how much pressure should you apply?

[Chris Jones]

I used Electrolube EML spray, no trouble so far and I hope it will prevent the copper wire from oxidising. It would be very posh if you could get the contact part of the windings hard gold plated!

[SeanB]

I measured and it was very intermittent on ohms. I thought about using an eraser but noticed while I was probing it was hard even to scrape any of the build up off.

I ended up cleaning it well with IPA first and used some 800 wet and dry sand paper (dry). Took a few wipes got most of it off, then used IPA and a clean rag. I also leveled the brush as it was a pitted.

When mounting the brush how much pressure should you apply?

Depending on the brush material about 5-30g of force to just lift it off the surface. For really big ones ( brushes that you can use on a truck starter or bigger) 100g or so. for those that handle welding levels of current they tend to have a spiral spring to provide the correct pressure.