706 



BELL SYSTEM TECHNICAL JOURNAL 



Some of the large telephone buildings house several central offices 

 and, in addition, administrative, engineering, commercial and other 

 departments. A joint incoming power servdce is often provided for 

 such a building, of which the initial telephone power plant requirements 

 may approximate 500 h.p. with an estimated energy consumption 

 approximating 1,000,000 kw.-hrs. per year. Provision for double this 

 demand in the ultimate mav be made. 



Fig. 3 — Typical large transformer installation for breakdown service when two 

 types of alternating current are furnished. Three 333-kv.-a., 11, 000/2, 200-volt 

 transformers supply frequency changer, these being in addition to the 60-cycle trans- 

 formers for regular service. 



The range of sizes is very great, varying from the above down to 

 the small "magneto" office which operates largely on dry cells and 

 other primary batteries, and may also take 1/8 h.p. to run a magneto 

 ringing machine from the power service. In such offices without 



