A little BS on BX cables.  Armored or Metal Clad Cables used in exterior installations.

Wenatchee and Chelan Real Estate Inspection Services.

Wiring in locations that are subject to “physical damage” will need protection. But what that protection is will depend on where the wires are installed and the environment of the installation.

As home inspectors we see a lot of wiring in locations that need protection. Many common areas I find unprotected wiring are in closets and cabinets.

But another very common area I find unprotected wiring during a home inspection is on the exterior of homes. Any wiring that is on the exterior of the home needs to be rated for use in damp or wet locations.

During a Chelan Home Inspection I came across the use of what is often called BX cable. BX is actually a brand name like Romex and Kleenex. BX is not defined as a term by the NEC and is technically called AC (armored cable).

Armored cable was first listed with Underwriters Laboratories Inc. in 1899 for the Sprague Electric Co. of New York.  It was originally called “Greenfield Flexible Steel-Armored Conductors,” after one of its inventors, Harry Greenfield. Some will refer to this cable as Greenfield cable. Armored cable (AC) first appears in the 1903 NEC.

There were originally two initial versions of armored cable. One was called “AX” and the other “BX,” with the “X” standing for “experimental.”  The “BX” version became the one that eventually was produced, and hence the name “BX” became the common name.BX became the registered trade name of AC Cable distributed by General Electric who had acquired Sprague Electric.

So “BX” is defined as “AC” cable (armored clad) and “MC” is defined as Metal Clad cable. These two cable assemblies are very similar in construction. (See note on FMC below)

The biggest difference between the two cable systems is that MC has full size ground wire while AC uses a combination of the jacket and a thin bonding strip or wire to function as the equipment ground. The bonding wire is unique to AC cable and this allows the outer metal armor in conjunction with the bonding wire to be used as an equipment ground.

Note: Early AC cable often does not have this bonding wire.

Now AC cable cannot be used in exterior or damp locations. Where MC Cable may be used in exterior applications but must be suitable for exterior or direct burial. This type of MC Cable will have a continuous PVC outer jacket.

Here are two examples from home inspections of AC/MC cables being used in exterior application that are not appropriate. As you can see they do not have a protective PVC outer jacket that would allow the use on exterior applications.

Knowing when and where a type of cabling system can and cannot be used is very important in electrical installations and is often a mark that a professional has not done the work.

Note: There is also FMC, (flexable metal conduit) called by the slang of "Greenfield" that comes without conductors installed.

“If you think it's expensive to hire a professional to do the job, wait until you hire an amateur.”

Red Adair

NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  

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