Hi all,

I tried to rewire a Universal 449-RS-WS dual 32W + 22W circline ballast from 1963, but while inside I hit some component (gallery post). Any clue what that component I hit is? The ballast still works, so I intend to use it, but to protect both my home and the ballast I'm going to add an in-line fuse.

The ballast is rated 118 volts and 0.95 amps. In testing, my Kill-A-Watt meter says the ballast pulls around 0.9 amps. A previous discussion here suggests 1- or 1.5-amp slow-blow fuses for the sort of use-case I am after. With a ballast rated for 0.95 amps, do you think a 1-amp slow blow fuse is likely to cause nuisance trips? I am thinking that the best approach is probably to buy both 1- and 1.5-amp fuses and if I get nuisance tripping from the 1-amp, size up to 1.5-amp.

In general, what method is best for calculating the appropriate amperage rating for fusing a ballasted fixture (fluorescent or HID)?

I would suggest a 1.5A fuse. If there's any significant fault then it will blow. 1.5A is not a whole lot of current in the grand scheme of things. If you do a 1A slow blow you probably won't have problems, but I just wouldn't do that.