maybe i should already know this but i was wondering when you need a fused disconnect and when you dont. i was telling a friend he needed a fused disconnect on a duct heater because it had no internal overloads. it just had a disconnect switch for working inside the heater

A heater would not require overloads. It is protected by the branch circuit over current device. A non-fused disconnect is fine in this application.

so what is a good rule of thumb to use fused or non fused. does every resistive load not need a fused disconnect.

Check the manufacturers nameplate. Most equipment will state weather or not a fuse is required. For instance, if a piece of equipment states a maximum fuse size of a specified value, you must use a fuse to protect the unit. Doing otherwise would void the listing and be a violation of 110.3(B). If it states maximum fuse or circuit breaker you could use either. You could use a breaker as protection and a non-fused disco at the unit.

thanks a bunch nick i guess i never thought of it like that.

Be careful on the AC/Heat pump units. Some say max fuse size and some say max fuse/HACR CB size. If it says only max fuse then you need the fuse (someplace in the circuit) regardless of the breaker.