BX Wiring (Old Armored Cable)

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).

Issues with BX Wiring

  • 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!
  • We cannot expand off it with new/modern wiring. Given it’s grounding issues, we cannot extend off existing BX wiring to add new 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.

Combination of Wiring Types

BX wiring was often installed along side of knob and tube wiring and ungrounded romex wire. Certain years, typically during the 1920’s and very early 1930’s that electricians had the choice of all three kinds of wiring. In some cases electricians at that time chose and continued to use one style of wiring throughout the home. More often we see all three styles mixed. You may be able to go into your basement and quickly identify the three types of wiring.

BX Wiring Process

Rewiring all different types of wiring works the same way. Some small holes will be necessary to fish the new wiring throughout the home.

For more in-depth information about the rewiring process of homes please click here.

Above is a great example of both BX wiring and knob and tube wiring working together. Notice the two black wires (knob and tube) leaving the same junction box as the BX wires (metal covered wires).

Estimate Process:


Customers that do have all 3 styles of wiring, we normally recommend our whole house wiring evaluation/mapping as we will identify where each kind of wiring is located. For more information of our evaluation please click here. There are cases where (and this depends on budget) one kind of wiring may be able to be preserved while others are replaced. We often see this when homes have both BX wiring and Knob and Tube wiring.

Customers may only want to replace the Knob and tube and leave the BX wiring.

  • If you have all BX wiring, or a combo of sorts but want to replace it ALL, a free in-home estimate will be just the ticket! To give a free estimate, we will shut down ALL the visible BX wiring in the electrical panel and walk through the home together, identifying all the outlets, lights, switches that are now OFF. When giving your estimate we will list a “price per point” for changes. Meaning, if any points (lights, switches, outlets) listed on your estimate DO NOT need to be replaced/rewired you will be due a credit (the price per point). If we find any other points that DO NEED to be replaced during installation, you will be charged the same amount per point. It goes both ways and is perfectly transparent!

A Homeowner’s Guide to BX Wiring Replacement

Was your home built before 1950? Are you planning to update your electrical system? This guide book will take you through the entire process including:

  • What is BX wiring? How can i identify it?
  • What are the issues with BX wiring and why should i replace it?
  • What are the steps to replacing it?
  • How invasive of a process is it
  • How do electricians estimate this kind of work?
  • How do i pick out the right electrician for me?
  • What to expect with contracts and billing.