Hi:

I am helping my brother update his electircal wires as I did at my house. One puzzling scenario that I do not know how to approach is the following:

The blower for his old furnace was wired with the old 2 conductor cable with no ground wire. When he had his new furnace put in, the contractor extended the old 2-wire conductor and dropped down from the ceiling to the furnace with a BX (two wires only) to power up the new furnace. We want to replace the 2-wire conductor with a new 3 wire Romex all the way to the electrical panel. My question is:

What should I do with the BX (about 5 feet of wire) wiring? How to ground the furnace with the third wire? Any help will greatly appreciated.

Thanks
Moe

 

You do not need three wire NM. Two wire (with ground) is all that's needed. You MUST terminate both wires in a metal box. Put the NM ground wire under a ground screw in the threaded hole in the back of the box, every metal box has one. Then just make sure the BX connector is nice and tight in the box. The cable and connector is the ground with BX.

 

As a side note to Speedy, Here in my area you cannot run romex directly to the furnace you must use bx at the furnace.

So you can run bx all the way to the main panel with a switch in between or like I do, romex to a box and then bx to the furance as you have.

 

Thanks for the reply. When I said 3 wire NM, I meant 2-conductor and a ground wire.

Exile, you mentioned a switch in between. What is the purpose of such switch? Is it to make it convenient to turn off the power to the furnace when needs to work on it? There is an on-off switch and it seems to have a built in fuse if I am not mistaken. Then a BX to a receptcle to plug in a condensation removal pump and the bx goes inside to the furnace panel where there is cut off switch. The green screw inside the furnace where the wires terminate has no ground screwed to it.

If I understood the replies, I run romex all the way to the metal box (the on-off switch) with the ground wire to the green screw in the box. Coming out of the on-off switch box I leave the BX 2-wire as is going to the inside of the furnace panel. Is this correct?

Thanks
Moe

 

Hello Moe, The furnace disconnect switch serves as an emergancy disconnect switch. You may use the Circuit breaker on your panel as such providing that you are not entering further in the room past the furance.(thus cutting off your exit) ie. the panel or switch are located as you are exiting the building and have already past the furnace. That is the code for us so you may want to check for your location.


As for the last paragraph that you have written, you are correct.