John, thanks for the correction.

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)


Tesla