secrets beneath the streets
ben franklin bridge
city hall
gold depository
peco substation
swann fountain
water department
in the sewer


PECO Independence Mall Substation

It is one of the largest underground substations ever attempted in the industry.

It is PECO Energyís first and largest underground substation.

It is the only PECO substation which is contained entirely underground.

Completed in 1966, Mall Substation took several years to plan and more than one year to construct.

The floor of Mall Substation is 30 feet below ground level.

In order to allow plants life to flourish above it, the roof of Mall Substation is 8 feet below ground level.

The substation is a big, concrete box, 75 feet wide by 225 feet long, with 21 foot ceilings and 18-inch thick walls. Because it is below the water line, the entire structure is encased in a waterproof membrane made of four-ply felt and bitumen (tar-like substance.)

The small, aboveground entrances (for personnel and equipment) were screened with red brick walls to blend with the colonial effect of the surrounding park.

The substation became necessary when construction of the Federal Court and Office Buildings at 6th and Market Streets meant the demolition of PECOís three-story Franklin Substation.

In order to complete Mall Substation, PECO developed three highly reliable duct seals which have since been adopted as an industry standard design for positive pressure seals.

Mall Substation is totally automatic and requires only periodic check-ins.

Mall Substation currently feeds electricity to 1,587 major Center City business customers.

Mall Substation was constructed in two sections separated by a concrete wall. The idea is to insure that one of the two sections continues to operate in the event of a major malfunction in the other.




Other resources

Peco Energy