Junction box for furnace

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paul32

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Minnesota
I haven't done tons of furnaces, but most have a junction box to splice the power conductors. Enter it though a 1/2" knockout (I use FMC). I've run across a furnace that has no junction box, and saw nothing special in the instructions. The pigtails to splice to are just free in the larger wiring area with lots of internal connections and the circuit board the termostat wires connect to. Is it acceptable to splice the incoming power in this space? I'm wondering about separation of the power and class 2 termostat wires. Or because this is in an appliance those rules don't apply? Or is it expected a junction box be added to the outside of the furnace?

About the junction box on the outside: I've seen the disconnect switch put in a box there and wondered how the box is attached. I would think it would have to have screws into the furnace for support, but what "zero-length conduit" goes between the furnace and box?
 
We typically mount a 1900 box to the side of the unit with self-drilling screws and use a 1/2" chase nipple between the box and the unit. To that we install the toggle switch disconnect. If you choose, splicing is permitted within the unit.
 
infinity said:
We typically mount a 1900 box to the side of the unit with self-drilling screws and use a 1/2" chase nipple between the box and the unit. To that we install the toggle switch disconnect. If you choose, splicing is permitted within the unit.
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I do the same... and run the manufacturer's leads out to it.

Hint... an outlet in the box for humidifier or boster fans can come in handy. :D
 
Thanks. I've seen a chase nipple before so don't know why I didn't think of it. That method would be good if there is no wall handy for a box for the switch, but I'm not sure it has an advantage otherwise. I already have a switch box on the wall, so in this case I'll splice in the furnace. Still seems a little odd if that is OK, why do most furnaces have a junction box (well, I suppose I could be seeing the minority of furnaces with a box most of the time, with limited exposure).
 
Paul,

Back east we would be required to install a "fire o matic" cut off over the

furnace, in case of fire the link would melt and open all power to it.
 
benaround said:
Paul,

Back east we would be required to install a "fire o matic" cut off over the

furnace, in case of fire the link would melt and open all power to it.
Click to expand...


Where exactly back East is that? I've never heard of it around here.
 
Treaver,

Back east in Mass. A gas furnace did not need one, but an "oil burner"

most certianly did, as well as an emg. shut off switch with special red emg.

cover plate. The oil burners normally were in the basement of the house.
 
Every Oil Fired heating system I wire gets a CUT OUT installed and a Emergency Switch outside the room of the heating equipment... Building Code of some sort...
 
benaround said:
Treaver,

Back east in Mass. A gas furnace did not need one, but an "oil burner"

most certianly did, as well as an emg. shut off switch with special red emg.

cover plate. The oil burners normally were in the basement of the house.
Click to expand...

I figured that it must have been an oil burner. I have never done one of those since everything around here is natural gas.
 
When I install my box on the furnace, I use a plastic snap in bushing... alot cheaper than any metal fitting... and I always install a disconnect switch and gfi on the boiler/furnace etc.... I usually use EMT out of the top of the box to a ceiling joist, Looks nice and is supported... plus you can run ty-rap your low voltage to it...
 
I run to above the furnace, install FMC from the ceiling down to a 4 square chase-nippled and screwed to the outside of the furnace. I find the chase nipple helps hold things in place while I screw the box on.

DaveTap said:
Hint... an outlet in the box for humidifier or booster fans can come in handy. :D
Click to expand...
It is legal to install a humidifier on the furnace circuit by 422.12, exception 1. However, if no humidifier is present and this is a prewire, an inspector could easily require it removed by stating it is a general purpose receptacle, since there is no appliance that the receptacle is currently powering at the time of inspection.

Also, if this furnace/receptacle is located in an unfinished basement, then the receptacle (prewire) would require GFCI protection according to 210.8(A)(5). If there is a humidifier present at time of inspection, a single receptacle could be used as allowed in exception 2 to that section.
 
georgestolz said:
Didn't those humidifiers take their supply from a 120V receptacle? Every one I've ever seen has. :)
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Mine uses 24v for the little motor, which I grabbed from the R and C terminals. As a bypass type, there is no blower.
 
yes some humidifiers only require 24V but even they need to turn on and off with the furnace blower. We often use an "accessory" lead to "switch" the outlet or install a 24v transformer on the box... its cheaper than the "current sensors" from April Aire :D
 
DaveTap said:
yes some humidifiers only require 24V but even they need to turn on and off with the furnace blower. We often use an "accessory" lead to "switch" the outlet or install a 24v transformer on the box... its cheaper than the "current sensors" from April Aire :D
Click to expand...

Why not use W and a fan sail switch in series with the humidifier?
 
stickboy1375 said:
No... I never use a receptace for 24v.... do you? What brand & model are you installing?
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I don't know what they were.

What they used was a transformer that plugged into a regular 120V AC receptacle, like what comes with cordless phone bases, phone chargers, etc. The tinner did the LV wiring, so I don't know how the humidifier knew when to turn on.
 
georgestolz said:
I don't know what they were.

What they used was a transformer that plugged into a regular 120V AC receptacle, like what comes with cordless phone bases, phone chargers, etc. The tinner did the LV wiring, so I don't know how the humidifier knew when to turn on.
Click to expand...

I would say the receptacle was energized on a call for heat... otherwise the solenoid would remain open....
 
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