Willis Lamm's
Traffic Signal Collection

(And Street Lights Too)

  Pittsburgh Transformer Co.
Series Street Lighting System

The Pittsburgh Transformer Company was founded in 1897 by Frederick C Sutter. The company manufactured a variety of industrial and line transformers. World War I brought a boon to the company's business and following the war they branched into manufacturing street lamp systems, most notably replacements for the harsh and maintenance intensive arc lamp systems.

Most early street light systems utilized high voltage series circuits. That design reduced circuit costs and allowed for central control over many lamps. (For a more complete description on how series circuits operate, please visit Understanding Series Circuits.)

Series circuits typically operated at high voltages with lamps strung in series. The voltage across each lamp was about 35 volts. The current was kept constant by regulating transformers and the total system voltage would adjust according to the numbers of lamps in the circuit.

One critical characteristic of a series circuit is that if a lamp failed, the entire string would go dark, so various innovations such as isolation transformers and cutouts were designed to keep the circuit intact as lamps burned out.

Series circuits required constant adjustment of circuit voltages as the load changed due to lamps burning out or being replaced. Early systems required someone in central stations to monitor and manually adjust the voltage on each circuit. Pittsburgh Transformer Company's approach was to produce a transformer that had various taps that would be connected depending on the total number of lamps on the circuit, and system voltage would be regulated by small shunt regulating coils located in each lamp. The idea was to improve circuit efficiency and reduce the need for constant monitoring by electricians.

The arm could be
lowered for relamping.

Pittsburgh Transformer Company's primary market involved industrial and line transformers, so their street lighting products were pretty basic - consisting primarily of one canopy or head design that could be equipped with four light distribution options.

Original list price: $ 9.60.

Original list price: $ 11.10.
Original list price: $ 9.60.

Original list price: $ 9.60.

The company also produced "stand alone" regulating coils that could be retrofitted to other brands of series street lamps for use on Pittsburgh series systems.

By the mid 1920s the development of automatic constant current regulators and improved series cutout devices rendered the Pittsburgh Transformer Company's design obsolete. Those innovations that followed are still in service today in some communities.

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Pittsburgh Transformer Co. "Type A" Street Lamp

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Early Line Material Radial Wave Street Light

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