This unmarked cover on Gold Street in Brooklyn is only a short distance from the first large electric generator station in Brooklyn, built by the Kings County Electric Light and Power Company in 1900. There are few other remnants of the KCEL&PC, with only a single lettered manhole cover known about a mile away on Hudson St. (see below) But the design and location point to a connection to the first Brooklyn AC plant.
The design is a well worn example of the often used open square design, popular at the turn of the 20th century. It is quite large measuring about 45 x 65 inches.
The 62 vent holes indicate it may have been a transformer point where the AC current generated at the Gold Street Plant was rectified to DC for use by the final customers.
This cover is at the corner of Gold St. and Front in the Vinegar Hill Section - right near the big Con Edison plant.