When a motor starts up, it takes a lot more power than it's rated run power.

Think of it like revving your car up to a nice steady 4000 rpm and dumping
the clutch.

Although a fuse wire will take a little while to melt, a P-N junction in a
semiconductor will snap like an axle when you exceed it's rating.

Typical electric motors draw 3 to 5 times more power when starting from a
stalled condition.

Hope this helps,
Peter

"Bob Engelhardt" wrote in message
...
I have a 25A SSR that is spec'd "motor load 7.2 FLA". What is it about
motor loads that require such drastic derating?

It is a zero-crossing relay, if that makes a difference.

Thanks,
Bob