This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
When connection is made between the inside wiring and the street main, a junction box such as that illustrated in Fig. 49 is employed. The three-wire system will probably be used on account of the economy in copper so obtained. The three mains, a, b, c pass straight through the box, but from the double terminals to which they are clamped are run the house leads a', b', c'. The whole set of couplings is enclosed in a cast-iron, water-tight box fitted with a cover, and the wires for the house service are protected by an iron pipe which extends from the junction box to the cellar.