Minimum Requirements For The Installation Of Step Up – Step Down Single Phase Low Voltage Transformers

9 May 2017

Reference #:  IB-EL 2017-02

The following Bulletin provides guidance for an acceptable installation of transformers. It deals with the location, disconnects, bonding, and grounding of single phase step-up, step-down 240v/600v/240v transformers and similar configurations. Design drawings prepared by a professional engineer in good standing with APEGBC must be provided for installations that deviate from the guidance provided by this bulletin.

This installation is an option where long distances are encountered and voltage drop is a consideration. See rule 8-102.

The following conditions apply to transformer installations:

  • Transformer impedance must match
  • Parallel conductors are not permitted in the intermediate system
  • Maximum of two transformers
  • Maximum voltage 750V at intermediate system

Part A:  Transformer Location

Rule 2-200 must be taken into consideration when determining a suitable location. A separate room or area restricting access to only authorized persons will typically satisfy these requirements. See also: Bulletin IB-EL 2016-05 sections D: Ventilation, F: Adequate Working Space, and H: Protection for Electrical Workers for further information on the requirements for the installation of this equipment.

Part B:  Transformer Disconnects

A disconnecting means must be provided in the primary circuit of each transformer, see rule (26-250).

This disconnect must be accessible and locked to prevent unauthorized access.

Each transformer shall be provided with markings indicating the location of the disconnecting means and other markings necessary to ensure safe and proper operation.     

Part C: Transformer Bonding and Grounding:

Equipment shall be bonded to the ground in accordance with rule 10-400, and the bonding conductor size shall not be less than that given in rule 10-814.

The 600V AC system between the step-up and step-down transformers shall be grounded, and the grounded conductor shall be identified.

The XO point on the secondary of the step-down transformer shall be grounded with a minimum #6 AWG at the distribution panel’s main neutral buss, or at the transformer, see rule 10-206(1).

 Typical Transformer Installation
Click to enlarge

Ulrich Janisch
Provincial Safety Manager – Electrical