No. With an EGC there would be an end to end ground even without the armor. What I'm assuming from the story was that the armor separated in half breaking the EG. Any Greenfield longer than 6 feet has to have an EGC run with the conductors.
But this whole story sounds fishy to me. Sprinklers? Fire system?
-Hal
The wiki article has a
archive link to the original fire report if you want the whole story I just skimmed it last night.
It describes exactly a situation I have seen many times, MC, FMC, or BX cable in contact with copper lines, I have seen it water water and refrigeration lines, this eats away the flex.
The report says it was galvanic corrosion between copper refrigerant pipes and 3/4" aluminum flex, Galvanic corrosion, vibration (from the compressor) and jagged edges resulting from poor workmanship (no red heads) during installation were the cause. The flex conduit was rendered un-grounded and was likely glowing, arcing and melting in the wall for a while.
The report has diagrams of the flex and says
"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 the metal studs"
The aluminum would corrode or dissolve prior to the copper tubing as the report noted it probably had been going on for 6 years.
There were other reasons the fire was so bad;
the Deli where the fire started was exempt from sprinklers as it was originally shown as occupied 24 hours a day on the plans and there was a exemption for areas occupied 24/7. the reasoning was a fire would be quickly noticed by occupants and contained with portable fire extinguishers. However in reality Deli closed from 2am - 8am and sprinklers were not added and this was not noticed on any fire inspections. the fire occurred when the Deli was closed. Had a annual inspection noticed the hours of operation they may have forced the Casino to add the sprinklers.
Other factors were the fire seemed to be in the perfect location to incapacitate the alarm system,
and since people still smoked indoors back then at least two witnesses had noticed a hazy smoke but figured it was just the Casino ventilation not keeping up with the smokers and did not report it.
It takes more than 20 amps to trip a 20A breaker and you probably cant even pass 20 amps thru a MC sheath. So if a short happens to the sheath all bets are off.
To me, and I am just a dumb electrician that read a fire report while watching TV, seems like a MC cable today could cause the same exact situation as this MGM fire.
