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Subchapter 5. Electrical Safety Orders
Group 2. High-Voltage Electrical Safety Orders
Article 27. Transformers (Formerly Article 76)
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§2877. Overcurrent Protection.

Each transformer or bank of transformers operating as a unit shall be protected against fault and overload currents by an overcurrent device in each ungrounded conductor in the primary connection. The protective device shall be permitted to be integral with or external to a transformer.

EXCEPTION: No. 1: On grounded systems, a relay in each of two phases, in conjunction with a ground relay, meets this requirement.

EXCEPTION: No. 2: More than one transformer or transformer bank shall be permitted to be protected by the same overcurrent device, provided the protection for each transformer meets the requirements of Section 2877 (b).

(a) Internal protective devices supplied integrally with a transformer shall be rated or adjusted in accordance with the specifications of the manufacturer.

(b) External protective means shall prevent the flow of current through the transformer in excess of the magnitudes and times in the following table:

Multiples of Transformer                 Maximum Time           
  Self-cooled Rating                      in Seconds             
      8Times                               300 Sec. 
   14.3Times                                 5 Sec. 
     25Times                                 2 Sec. 
     50Times                               0.5 Sec. 
    100Times                             0.125 Sec. 

(Title 24, Part 3, Section 450-3.)

NOTE: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code; and Section 18943(c), Health and Safety Code.


1. Editorial correction filed 11-2-83 (Register 83, No. 45).

2. Amendment filed 12-10-87; operative 1-9-88 (Register 88, No. 1).

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