In the interests of safety, most modern deep fat fryers say NO lard, butter, etc. (hard fats). The manufacturers don't say why but I've heard many people conjecture that lard heats up, smokes, maybe burns when exposed to fairly high temperatures (over 370F. or 185C.). My theory is that the heating coils on the deep fat fryer overheat the lard if it is used in its hard form.
We have real lard (from a real pig raised on a real farm -- not a huge farm where pigs lead a short and brutal life). Then we rendered it ourselves which is not hard at all.
We are just about to try cooking french fries (British, chips) in our new deep fat fryer. We have melted the lard, strained it and poured it in, as one would with canola oil, etc.
Wish us luck, please. I'll try to report back on this scary adventure in cooking!
UPDATE: Okay, that didn't work too well. The fries never did brown even after 15 minutes at 320F. and then 12 minutes at 370F. (ordinarily 5 to 7 minutes at the lower, cooled, then 2 minutes at the higher). Cooked but not browned. So I threw a few in a fry pan and burned them a bit. Oh dear. Did I mention we are at 3000 feet above sea level? This makes a bit of a difference in cooking. My friend (bless her heart) said she loves blond french fries and ate them up. I was not quite so pleased!