HVAC electric questions.

[GG]

(1) When you run NM (romex) cable into a closet to supply power to an air handler does that NM cable have to be protected in some type of coduit, and if so what NEC code applies to that installation? I see NM cable installed all the time in a closet without protection, and it looks dangerous.
(2) I see alot of times when a gas furnace has a screw in fuse / switch combo located near the furnace as a means of disconnect. Is this done because the furnace nameplate says that the circuit must be protected by a fuse and not a breaker? I dont understand why you cant just use a single pole light switch to disconnect the HOT at the furnace. I mean the circuit is protected back at the breaker box. The screw in fuse seams unnecessary.
(3) If you install a breaker that has a means to lock it in the open position are you still reqired to supply a disconnect at the condenser or air handler or both? What section of the NEC covers this?

 

[mdshunk]

(1) When you run NM (romex) cable into a closet to supply power to an air handler does that NM cable have to be protected in some type of coduit, and if so what NEC code applies to that installation? I see NM cable installed all the time in a closet without protection, and it looks dangerous.

I guess that's more of a personal decision, or perhaps you have local rules that will clear that up. Myself, I think it looks a bit ugly, but I fail to see how it's going to get damaged in a closet. Maybe you store shovels, axes and broken glass in your closet? :smile: In any event, if it comes up through the floor, the NEC only requires protection for a short piece right there at the floor.

(2) I see alot of times when a gas furnace has a screw in fuse / switch combo located near the furnace as a means of disconnect. Is this done because the furnace nameplate says that the circuit must be protected by a fuse and not a breaker? I dont understand why you cant just use a single pole light switch to disconnect the HOT at the furnace. I mean the circuit is protected back at the breaker box. The screw in fuse seams unnecessary.

For modern furnaces, you can use a snap switch for the most part. There are a couple reasons why guys still use the fuse/cover units. One is tradition, since older furncaces actually had called out that they needed a 6 or 8 amp fuse, written right on the dataplate. Also, some of the modern AHU's only require a 15 amp circuit, and the original electrician might have ruffed in a 20 amp circuit. Easier for the HVAC man to install a fuse/cover unit with a smaller fuse then to go mussing about in the panel.