You need to use section 426-Fixed Outdoor Electric Deicing and Snow-melting Equipment, instead of 424, that is for space heating equipment.
420-50 (a) of the 99 NEC talks about the disconnect for tracer cable. This section talks about switches being used for the disconnect. So if you use a switch, then 380-2(b) can be used.
I am assumming you are using the 99 code?
Anyway I hope this helps.