Need some feedback

[JohnJ0906]

I want to run this past you all and get some input.
Service call today at a commercial establisment, approx 15 seperate suites. 1 suite totally without power, boss sends me out.
Customer says they heard "a loud pop" from the back, and power went out. also thermostat had acted "squirlly" when they got there in morning
Went to the suite,208/120 3 ph MLP,Challanger brand, no breakers tripped, no voltage. Went to the meter room, Challanger meter stacks, 150 amp 3 ph Challanger breaker in "ON" position. No voltage load side, when I tried to move to "OFF", stopped in middle posion and wouldn't budge. Luckily there were several meter sockets not being used, so I could swap breakers. No shorts on the feed, reenergize panel in unit with everything off, Now I have power.
Turn on 120 breaker 1 by 1, everything works. I am left with:

Furnace, 3 ph, 60 amp fuses
Duct heater, 3 ph 40 amp fuses
RTU, 3 ph, 30 amp fuses
Water heater, 1 ph, 30 amp breaker in panel All of the above fuses are still good.
Turn on water heater, run water, heats it, OK.
For the HVAC equipment, I went to each 1 at a time, checked fuses, checked for shorts in the feeder, reenergize w/ disco off, all OK.
I turned furnace and ductheater back on, but I didn't turn on RTU, I didn't see any damage, but it had a fair amount of rst on the compressor.
I told the customer to have the HVAC system checked carefully, because my best guess was that a fault in something caused the problem, or it could have been that the main breaker had gone bad.
My questions- If a peice of equipment faulted bad enough to trip a 150 amp main breaker, AND render it inoperable, why not also trip the individual breaker as well, and why not the fuses?
-If the main breaker just decided to go bad, why would the customer hear a "POP" with 2 suites, and at least 1 block firewall between her and the breaker?
And the big question-What the @&%#$ did I miss here?
Thank you in advance for any and all replies.

[lowryder88h]

:-? Reading your problem you listed above , it seems to me that the load on the main cb was close to its 80% capacity. the loads are accumalitve on the main and not on each individual branch circuit. IMHO

[charlie b]

The problem could have been just the main breaker. Nothing is immune from failing. It could have just been its turn. The failure sounds internal to the breaker, and not necessarily a result of overcurrent. If you still have the breaker, perhaps you could do an autopsy, to see if there are any indications of the cause.

As to the client hearing the sound through several walls, that should not be a surprise. People will react to sounds that are unusual (i.e., not a part of their normal daily experiences), even if the sounds are not loud.

[al hildenbrand]

As to the client hearing the sound . . .Following on Charlie's comment: The sound the client heard may have been unrelated to the electrical failure, merely co-incident to it. The non-technical observer can, occasionally, make some quite fanciful associations.

I like Charlie's idea of a post mortem on the breaker.

[bradleyelectric]

when federal went out of business, they formed a company known as challenger. Quality wasn't any better in the new company.

[JohnJ0906]

I was a little surprised to see a 3 phase Challanger panel. I was more surprised to see the meter stacks and all Challanger! As for the breaker, it's still there. At some point they made 2 units into one, and made both feeders come from from 1 meter , I used the one left over, and had to use the bad one to fill the hole left.
edit to add: Are replacement breakers for this available?

[mdshunk]

when federal went out of business, they formed a company known as challenger..I thought that Challenger was a failed Cutler-Hammer brand?