BX CABLE REVISITED
In the March 2000 Ol' Professor column, I spoke of a fire started by a BX cable. I received a letter from Prentice Cushing (see Letters to the Editor, page 46). He's a senior member of the Institute of Electrical and Electronics Engineers and a fellow of the American College of Forensic Examiners.
He writes: "If a neutral conductor on the service entrance opens, then the only neutral path becomes the ground (not intended to carry current), and I have seen many cases where the BX armor became the path from a fault to where the cable touches a water pipe and supplies a water pump or water heater; as a result, the armor overheats and starts a fire."
Regarding the above paragraph, a number of years ago, the Smithsonian Institution suffered a devastating fire. A large display with hanging sheets of clear plastic and a number of electrical devices was built up on a wooden platform. As a result of some defect, the entire mass of armored cable became "like a large toaster." This fire has a number of useful points which I will relate in a subsequent column.
