The MGM fire originated at a FMC connection to a display cooler in the Deli area.
From the The MGM Grand Hotel Fire Investigation Report
The metal raceway (tubing) acted as the “grounding” conductor in the side stand. Through examination of the raceway in and over the side stand, it was determined that a ground fault condition did exist prior to the fire. The O/Rs observed several loose connections between the junction box connectors and the flexible aluminum raceway.
Portions of the raceway were unwound and unconnected. Arcing was observed where the raceway and E.M.T. chase came in contact with each other and where the raceway came in contact with each other and where the raceway came in contact with the metal studs. ... Improper installation and exposure to the warm atmosphere surrounding the raceway caused the insulation surrounding the copper conductors to loosen and deteriorate, exposing the bare copper conductors. Short circuiting occurred in the exposed copper conductors because only two conductors existed (no ground). Installation of the raceway to the junction boxes was faulty, and the ground could not function the way it was intended. The delayed action caused the electrical current to attempt to seek a ground; when it could not find a ground, it caused the copper conductor to become warm and eventually hot. This in turn caused the raceway to overheat to the point of glowing metal. This caused additional heat build up in the area approximately 45 in. from floor level in the soffit area. The lack of proper ground equipment for the conductors to provide a low impedance rate to carry the fault current to trip the breaker allowed a longer period of time for arcing to occur. This arcing produced that amount of heat needed for ignition temperature. Electrical fires can occur even when properly operating circuit protection is installed. As an example, loose connections at termination points can cause this effect.
(For the purposes of this report, the term O/R or O/Rs designates the officer or officers reporting, terminology which is in fact applied to Clark County Fire Department Fire Investigators in all written communications.)
[This message has been edited by resqcapt19 (edited 07-02-2005).]