Copied from Teslas comments in the Photo Gallery section:
1200A can (barely) be seen next to each bus -- down low.
The 600A frame size fuses are ganged because -- at one time -- that was a popular size limit for 250VAC fuses (blade style)
The operative assumption was that such matched sets would blow in sequence and that they'd always be replaced in pairs -- if not the entire sextet.
IIRC, this disconnect feeds a major retail establishment -- and the power flow is backwards: line is at bottom, load is at top.
It feeds a distribution panel on the other side of the wall... just as ancient. Consequently, these fuses did not have more than a prefunctary purpose. The many smaller fuses just a few feet away would protect the branch conductors and all sub-feeders.
These (MAIN) fuses could then only blow if some anarchist placed a bomb at the distribution board. (!)
You'll note that they did their duty for decades on end.
It was installed generations ago. (30s to 40s?)
The NEC at one time required disconnecting means exterior to any structure.
(In the very beginning the switch was to be thrown OFF when a building became unoccupied.)
This safety switch was probably installed per the Fire Marshall's specifications. Being in an urban setting, the line side power was coming in from below. Rather than fuss and bother, the power flow through the switch was simply reversed.
Obviously, none of it would fly today: exposed bussing, wrong way power flow,... even the fuses are standard blow -- not slow blow. Also note the extremely wide single layer copper bussing. It's simply not done anymore.
Today the Fire Marshall would be satisfied by a shunt trip MAIN for his crews. The entire box would never be necessary.
From my memory, this was the MOCP for the 120/208 service feeding this two story (w/basement) department store that was there for many, many years.
The building was a triple net long term lease that did not require a lot of visits from the owners property mgt team. This was the first time I was on site to prep the building for the upcoming vacancy and existing evaluation.
The top buss is the utility feed which came thru the masonary wall; load buss went down into a buss troff that the subpanels and discos were fed from. Yes, buss in a troff.
An assumption was made that the line side came from the UG utility vault street side,as was the 'usual' in the city.
Wrong! The other side of the wall was a transformer vault (utility)! Seems that way back, some agreement was made to have the utility 4160 pots in a 'vault' within the basement.
The POCO had a really tough time admitting the pots were theirs, along with the PCBs!
Yes, this building was electrically 'aged' in Dec 2002! It underwent a wall to wall interior demo, down to the bones.
I rewired the Wakefield building. (17th Street downtown Oakland, California)
Plan A was to have PG&E place transformer vaults below grade immediately exterior to the building.
It was rejected once the underground 'traffic' became apparent. The Area Code 510 exchange was, and remains, located directly across the street. BART also runs very close by. During its construction no end of underground utilities were shifted over (and under) 17th Street.
I was told that these utilities go straight down over 35 feet -- packed in at every level almost from curb to curb.
Plan B had PG&E placing Poco owned twin 750 kVA transformers inside a custom vault -- dug out from under the building to get vertical clearance.
For reasons of fire liability, the vault was a full foot thick -- to include the pad. I had to provide multiple ground rods per the Poco scheme. One corner was so sandy that I could push the rod in with my bare hand!
PG&E also specified that the feed was to come by way of bus duct. (just a tap assembly was used at the wall penetration)
Thence the current was fed through (8) 3" GRC paralleled feeders to the 3000A MAIN. All of this was encased in concrete. The project was a beast.
This is the only transformer vault that I've come to know. I suspect that similar schemes dot the North American urban landscape.
One last bit: the transformers could not be directly placed. They had to drop them down -- and then hydraulicaly winch them over into position. This method had become a standard practice for PG&E.
BTW, Wakefield is a historically designated building. (1927, first 'skyscraper' in Oakland -- it had 8 floors)
That place still brings back a lot of bad memories. (9-11-01)