BX wiring, also known as armored cable is the 2nd generation of wiring used in homes. It first appeared in the 1903 National Electrical Code (NEC) book. It became popular in the 1920’s and by 1932 or so was the main wiring type used up until the late 1940’s when it was replaced by early romex ( non-metallic sheathed cable).
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BX Wiring Issues
Relies on the outer coverings to maintain a ground path. Each time a BX wiring circuit went in and out of a box, it used a special connector with a lock nut. This lock nut and connector had to be tight, otherwise the circuit would lose it’s ground path. Let’s say the circuit goes in and out of 10 different boxes (outlets, lights etc) before the circuit finishes.
If some or all of these connectors are loose, the ground connection get’s worse and worse as you go down the line. We see this a lot, where we are measure voltages and have say 120 volts between hot and neutral, but only 60 volts between hot and ground. This is a sure sign that the connectors are loose throughout the circuit, and this can be a difficult thing to solve without replacing the wiring itself.
This becomes a safety hazard if there is a short circuit to ground, the breaker/fuse may not trip now, because the ground path is no good. I’ve heard older electricians telling stories that the metal outer covering will become a resistor, potentially turning red hot!
Electricians cannot expand off it with new/modern wiring. Given it’s grounding issues, we cannot extend off existing BX wiring to add new wiring.
BX Wiring uses a rubber with cloth insulation over the copper wires. This kind of insulation is especially sensitive to heat. Older light fixtures had NO insulation within them to protect the wiring above from the heat of incandescent light bulbs. People would then install larger 100 watt incandescent light bulbs in these fixtures and in turn would cook the wiring in the junction box above. We have seen MANY junction boxes with insulation that crumbles apart once the light is removed. Scary stuff!
BX wiring was installed with 2 prong outlets. 2 Prong outlets will not accept cords that are 3 prong.