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I wonder if this is a remnant of the 1893 World's Columbian Exposition and the "Current War"? This is on Jackson Park's Wooded Island. It says: "Westinghouse Electric & Mfg. Co. Alternating System. Grimshaw Insulated Wire White Core." #ManholeCoverMonday 
The 1897 National Electrical Code manual includes a listing for "Grimshaw (White core) N.Y. Insulated Wire Co." linghunt.com/101Spearfishin…
As the Tesla Memorial Society says, the 1893 world's fair in Chicago "was the final great victory of Tesla/Westinghouse's Polyphase Alternating Current system electricity over Edison's Direct Current (DC)." teslasociety.com/columbia_expo2…
