Induced voltages and currents in metal armour or sheaths of single-conductor cables
(see Appendix B)

1) Where sheath currents in single-conductor cables having continuous sheaths of lead, aluminum, stainless steel, or copper are likely to cause the insulation of the conductors to be subjected to temperatures in excess of the insulation ratings, the cables shall be

a) derated to 70% of the current-carrying rating that would otherwise apply;
b) derated in accordance with the manufacturer’s recommendations and in compliance with Rule 2-030; or
c) installed in a manner that prevents the flow of sheath currents.

2) Circulating currents in single-conductor armoured cable shall be treated in the same manner as sheath currents in Subrule 1).

3) Single-conductor cables and single insulated conductors carrying more than 200 A shall not enter ferrous metal boxes through individual openings.

4) Where single-conductor cables and single insulated conductors carrying more than 200 A enter ferrous metal boxes, precautions shall be taken to prevent overheating of the wall of the box by induction.

5) Precautions to be taken to prevent overheating of the metal shall include the use of non-ferrous or non-metallic box connectors or cable glands, locknuts, bushings, and ground bushings.

6) All cables and insulated conductors making up a circuit shall enter the box through one common non-ferrous or insulating plate having a minimum thickness of 6.0 mm unless a deviation is allowed in accordance with Rule 2-030.


7) Where single-conductor mineral-insulated cables are used, all current-carrying conductors shall be grouped together to minimize induced voltage on the sheath.

Source: Rule 4-008, CSA C22.1:21, Canadian Electrical Code, Part 1 (25th Edition), Safety Standard for Electrical Installations. © 2021 Canadian Standards Association. Please visit