Guide to the Canadian Electrical Code, Part I — Instalment 37

 

May 7, 2018

By William (Bill) Burr

In this article: Section 74 — Airport installations. This series of articles provides a guide to help users find their way through this critical document. This is not intended to replace the notes in Appendix B or the explanations of individual requirements contained in the CEC Handbook** but will hopefully provide some help in navigating the code.

Airport installations are series-type circuits that differ from other multiple-type circuits in that the regulator supplying them provides a constant current, variable voltage supply regardless of the load. The regulator does not respond to ground faults in a normal fashion. A single ground fault does not affect the whole system. Two or more ground faults affect only a portion of the system or a reduction in lighting intensity. A ground counterpoise is provided to protect service personnel from touch voltages when repairing or replacing broken luminaires. The CSA Handbook provides an in-depth explanation of this technology.

Rule 74-000 notes that this is a supplementary or amendatory section of the code and applies to installation of series-type constant-current circuitry supplying airport visual aid systems, including airport runway, taxiway, and approach lighting. Appendix B notes that these installations be designed by a civil engineer in accordance with good engineering practice and that the design be acceptable to the airport authorities.

Rule 74-002 contains definitions for special terminology used in this section for ground counterpoint, mounting stake, series isolating transformer, and transformer housing. It is important to understand these terms because of the special electrical characteristics of the series-type circuits used in these installations.

Rule 74-004 specifies the wiring methods for airport installations and includes:

• type ASLC cables for the series system
• using requirements of rule 12-012 and Table 53 for buried cables in public areas of airports
• for areas not accessible to the public, single conductors and cables must be installed
  • at least 450 mm deep when installed in raceway
  • at least 450 mm deep and covered with at least 75 mm of sand or screened earth above and below the conductors when direct buried
  • with mechanical protection consisting of rigid conduit or concrete encased raceway buried at least 600 mm deep when installed under runways, taxiways, aprons and roads
• where installed within a concrete or asphalt surface must be in a raceway
• when directly buried in a trench have
  • 75 mm lateral separation between different series circuits
  • 300 mm lateral separation from low-voltage or control cables
  • 75 mm vertical separation in crossovers
  • 300 mm vertical separation of low-voltage cables crossing over in the upper position
• Identifying each cable with a cable marker at each point where the cables are accessible at maintenance holes, transformer housings and other similar locations.

Rule 74-006 requires that direct buried series isolating transformers:

• are installed so that the transformer and primary leads are a minimum depth of 450mm
• that secondary conductors are colour-coded with one conductor identified
• that secondary conductors are polarized with the identified conductor connected to the larger pin or receptacle and grounded

Rule 74-008 requires that a ground counterpoise be installed with a series lighting system.

Rule 74-010 requires that ground counterpoise conductors be

• minimum #8 solid soft copper
• insulated with a green finish where installed underground in raceways
• placed 75mm above all cable in the trench
• run in a zig-zag pattern crossing cables at 300mm intervals where outer cables are more than 150mm apart
• placed 75 mm over non-metallic conduit and under any protective covering
• connected to
  • ground terminal of each series isolating transformer;
  • the mounting stake of light units;
  • the sheath of metal sheathed and armoured cables supplying light units;
  • ground electrodes at all regulators, towers, and lighting equipment, and maintenance holes;
  • metallic transformer housings, lids and covers;
  • non-current carrying metal parts of inset lights; and

• bonded together at all points where counterpoise conductors of different systems cross or come together.

In the next instalment, we will be discussing Section 76 — Temporary Wiring.

* The source for this series of articles is the Canadian Electrical Code, Part I, published by CSA.

**Note the CEC Handbook is also published by CSA.

William (Bill) Burr is the former Chair of the Canadian Advisory Council on Electrical Safety (CACES), former Director of Electrical and Elevator Safety for the Province of BC, and former Director of Electrical and Gas Standards Development and former Director of Conformity Assessment at CSA Group. Bill can be reached at Burr and Associates Consulting; billburr@gmail.com