Find the Answer
Although it's very hard (if not impossible) to see in the photo, the old Type AC armor clad cable (BX) on the left is abandoned and does not connect to this plastic box. However, someone did add the new Type AC cable on the right to serve an outlet about 10 ft away. The keyless lampholder was originally supplied power via the nonmetallic sheathed cable.
The first problem with this installation is this type of nonmetallic box is not designed to be used with metal armored cable assemblies. Even though there are exceptions (noted below) that offer ways in which metal raceways or metal armored cables can be installed in nonmetallic boxes, this box comes equipped with entries for nonmetallic cables only.
Here is the requirement as outlined in 314.3.
"Nonmetallic boxes shall be permitted only with open wiring on insulators, concealed knob and- tube wiring, cabled wiring methods with entirely nonmetallic sheaths, flexible cords, and nonmetallic raceways.
"Exception No. 1: Where internal bonding means are provided between all entries, nonmetallic boxes shall be permitted to be used with metal raceways or metal-armored cables.
"Exception No. 2: Where integral bonding means with a provision for attaching an equipment bonding jumper inside the box are provided between all threaded entries in nonmetallic boxes listed for the purpose, nonmetallic boxes shall be permitted to be used with metal raceways or metal armored cables."
Thanks to Robert Pagliuca, an electrician from Watertown, Mass., for sending in this photo.