Inspection Detail

Inspection: 300553161 - Quigley Heating And A/C

Inspection Information - Office: Dallas Area Office

Investigation Summary

A heating and air conditioning contractor was hired to install a combustion air duct in a residential heating system. The 203-millimeter-diameter duct was to be installed about 760 millimeters above the floor in a closet enclosing the heating system. An employee assembled the duct in the attic, dropped it into the closet, and suspended it from a rafter with corrugated iron. He went to the closet and noticed that the area in which he had to work was very tight. He removed a gas line and squeezed into the closet to place additional screws in the duct. A metal box housing the fused, single-pole disconnect switch for the furnace was located on a wall adjacent to the furnace. To approach the duct, the employee had to place his back against the box. The circuit conductors supplying the disconnect box were run as metal-clad cable. The disconnect box supplied power to the furnace through a three-conductor jacketed cable containing three No. 16 AWG stranded copper conductors. All three conductors were exposed for a length of about 13 millimeters midway inside the furnace. One of the conductors was touching the metal frame of the furnace. The copper wire had signs of oxidation, indicating that this was an old break or a failure in the cord's insulation. No strain relief or bushing was present on the jacketed cord where it entered the furnace. The employee had his back against the metal disconnect box, and the cable to the furnace was across his shoulder. The homeowner's mother heard a grunt and rushed to the employee. When she tried to pull him out of the closet, she felt an electric shock, so she summoned emergency medical assistance to rescue the employee. Unfortunately, the rescue efforts were to no avail. The employee had been electrocuted. He had burn marks on his back. After the accident, signs of arcing were noted where the armor-clad cable was attached to the metal disconnect box. An examination of the wiring discovered that 40 volts, ac, were present on the conductors touching the furnace frame. When the conductor was moved away from the frame, the voltage rose to 120 volts.

Keywords: ENCLOSED SPACE, FURNACE, ELECTRICAL, ELECTRIC CABLE, E GI VII, ELECTROCUTED, GROUND FAULT, EQUIPMENT GROUNDING, ELECTRICAL BOX