Originally Posted by Bowtiebrewery
Not to be a bit-picker, but it's V=IR and P=IV - but the math is correct.
I would suggest a circuit breaker on the heating element power supply and fuse to protect the PID if you wanted.
That PID is AC powered, so to protect it you'd fuse between the 110V and the PID. It's rated at <5 watts, so you'd need a ~50mA fuse. I'd get a fast blow.
A fuse on the 12V line would protect the SSR output of the PID in the event the SSR failed to a short somehow. It's rated for 30mA out, so I'd get a 30mA fast blow.