TRANSFORMERS
City of Palo Alto
Building Inspection Division
285 Hamilton Ave.
Inspection Request: 650 329-2496
Revision Date:2011
General Requirements/Checklist for:
Commercial
Codes Enforced:
2010 CEC
Palo Alto Municipal Code (PAMC)
Building Division
The information provided in this document is general and intended as a guide only. Each project is unique and
additional requirements may be enforced as deemed appropriate.
 Determine size in KVA on engineer’s plans.
 Check the name plate on the transformer for KVA and primary and
secondary voltage. (CEC 450.11)
 Verify primary circuit conductor gauge and over current protection (CEC table
450.3(b)) & 240.21 (c)(1)
 Verify room ventilation. (CEC 450.9)
 No storage is allowed on the transformer.
 Maintain working clearances. (CEC 110.26)
 Verify secondary circuit conductor gauge and overcurrent protection. (The
secondary OCPD can not sized for the next higher rating. CEC 240.21(C))
 Grounding electrode conductor connection (close as particle to a metal
water pipe or structural metal. (CEC 250.30 (a)(7))
 Bond metal water piping in nearest area being served by transformer. (CEC
250.104 (d)(1))
 Provide a main bonding jumper from the xo terminal to the ground
termination lug. (CEC 250.104 (a)) The equipment grounding conductor and
the bonding strap will also terminate at this ground lug.
 Grounding electrode conductor (size) based on the derived phase conductors
(output) (CEC 250-30 (a)(3))
 Secondary conductor overcurrent protection shall comply with CEC 240.21 (c)
(2-6)
 The secondary overcurrent protection device shall be within 10’ of the
transformer. (CEC 240.21 (c)(2))
 Verify main bonding jumper size (CEC 250.28 (d) & 250.66). Where phase
(secondary) conductors are larger than 1100 kcmil the jumper shall be sized
at 12 ½ % of the circular mil area of the phase conductors. Connection shall
be at the source or the first system disconnecting means.
 Verify primary and secondary conductors are in flex conduit for vibration.
 Verify required clearance and ventilation openings as provided on the
manufacturer’s nameplate. (CEC 450.11)
 Verify available short circuit current to determine suitability of panel board.
 Where transformers exceed 112 ½ kVA and where the insulation system is
less than a Class 155, they shall be installed in a 1 hour rated room or
enclosure. (CEC 450.21(B))
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