PECO Independence Mall Substation
It is one of the largest underground substations ever attempted in the
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.
order to allow plants life to flourish above it, the roof of Mall Substation
is 8 feet below ground level.
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
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.
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.
is totally automatic and requires only periodic check-ins.
Mall Substation currently feeds electricity to 1,587 major Center City
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.