My gas furnace will not turn on. I verified 120V where the armoured cable enters the furance, so I was going to continue testing for voltage before and after the transformer (with the door safety switch pressed in and 24V call-for-heat manually triggered, flame safety module is good), but I noticed a broken bit of (aluminum) wiring at the green ground screw. The black and white wires are solid copper. I assume the aluminum wire inside the armoured cable is ground, and was wrapped a couple times around the outside of the metal sheath, and then finally connected to the green ground screw.
Is using a short strand of solid copper ground wire, with the copper wire screwed into the grounding screw, and pigtailed to the aluminum wire with an AlumiConn the best practice?
Quck note – I'm comfortable and confident with the gas-related safety components on a gas furnace, but aluminum wiring requires special knowledge and is a source of fires, so I'm super cautious.
Best Answer
Someone forgot a fitting
Normally, armored cables (like yours) are brought into a box using a fitting designed to clamp the the cable armor, grounding it to the box and also providing a strain relief for the cable inside. Your furnace installer didn't have that fitting on hand, though, so they simply shoved the cable through the hole and shoved a "redhead" bushing into the end of the cable to protect the wires inside, leading to the mess that you see here.
So, with the breaker off, I would undo that armored cable (including taking the "redhead" out), get the correct fitting, insert the fitting into the KO and hold it on with a locknut, cut the bonding strip off at the end of the cable armor and insert the cable into the fitting, insert the "redhead" into the armored cable again, and reconnect the hot and neutral wires. Then, you'll at least have this furnace properly grounded.