4-010 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 carrying more than 200 A shall not enter ferrous metal boxes through individual
(4) Where single conductor cables 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 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.