Uncle Peter wrote:
Does reducing the resistance affect the wattage rating
of a power rheostat? I'd imagine it does, but I'm not
sure how it would be derated..
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The power rating of a rheostat is based upon its total resistance R.
allowing for a max current I with P(max) equals I*I*R

If the adjustable resistance is reduced to say 1/5 of the total
resistance that reduced resistance can accept the same current I .
This means the power rating has been reduced by a factor 5 ,in other
words the power rating is proportional to the set resistance.

Frank GM0CSZ / KN6WH