June 3, 2020

By William (Bill) Burr

The code is a comprehensive document. Sometimes, it can seem quite daunting to quickly find the information you need. In this current series of articles, I will provide 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 while reading the code. Here in this issue: Section 18.

Section 18 covers installation of electrical equipment in hazardous locations as defined in Section 0, such as areas in which there is a potential for the ignition of explosive gases or combustible dusts, fibres or flyings due to the design, installation or use of electrical equipment. Since the information in this instalment is extensive, it will be presented in two parts. This is Part A.

Rule 18-000 outlines the scope of this section, which is a supplementary section of the code and as such outlines additional or supplementary requirements for the selection and installation of electrical equipment in hazardous locations. In addition, Section 18 uses the international zone system of area classification; however, in cases of addition or renovation to an existing installation classified to the Division system, the electrical equipment may be chosen and installed in accordance with Appendix J – For existing installations using the Class and Division system of classification of the code. Also note that additional information is available in Appendices B, F and L.
Rule 18-002 provides special terminology definitions for terms used in this section, which are additional or supplementary to the definitions in Section 0.

Rule 18-004 divides the classifications into explosive gas atmospheres or explosive dust atmospheres. Reference material for area classification can be found in Appendix B. To use Section 18, the classification of the area in which you are working must be determined by qualified persons and authenticated by a person assuming responsibility for the classification. Note that installations within the scope of Section 20 are classified under that section.

Rule 18-006: locations containing an explosive gas atmosphere are divided into zones 0, 1 or 2 depending on the frequency of occurrence and duration of an explosive gas atmosphere. Appendix B and L provide typical examples of explosive gas atmosphere classifications.

Rule 18-008: locations containing an explosive dust atmosphere are divided into Zones 20, 21, or 22 depending on the frequency of occurrence and duration of an explosive dust atmosphere. Appendix B and L provide typical examples of explosive dust atmosphere classifications.

Rule 18-010 specifies that alterations or repairs to equipment must be authorized and not be made to live equipment. In addition, this rule specifies that electrical equipment in hazardous locations must be maintained in its original safe condition. Again, Appendix B provides additional guidance in developing proper maintenance procedures.

General

Rules 18-050 to 18-074 apply to all hazardous location installations, both explosive gas and explosive dust atmospheres.

Rule 18-050 specifies that the code requires that electrical equipment used in such locations be suitably designed, tested, and certified for the specific explosive atmosphere that will be present. This rule also provides groupings of various explosive gases and combustible dusts and fibres for which electrical equipment must be suitable. It also provides a hierarchy wherein electrical equipment suitable for a preceding group may also be suitable for a latter group.

Rule 18-052 lays out the marking requirements on electrical equipment intended for use in hazardous locations. Additional information on marking is listed in Appendix B.
Rule 18-054 requires that in Zone 0, 1 and 2 locations, equipment with a marked internal or external surface temperature, (or 100 degrees C, if not marked), equal to or higher than the ignition temperature of the combustible gas, must NOT be installed in that location. This is true even for equipment that is not required to be approved for hazardous locations.

In Zone 20, 21, and 22 locations, equipment with a marked external surface temperature equal to or higher than the lower of the dust cloud or dust layer ignition temperature, must NOT be installed in that location. While there is no definition of ignition temperature in this section, Table 18 provides a summary of what equipment types are suitable for installation in the various hazardous locations.

Rule 18-056 requires that every separate area, section or room must have its own hazardous location classification.

Rule 18-058 requires that if equipment rooms are intended to be not classified as hazardous locations, they must be constructed of substantial, non-combustible materials and in such a way to ensure they remain hazard free. Where the equipment room communicates with a Zone 2 or an explosive dust atmosphere, it must be separated by close-fitting, self-closing doors. Where the equipment room communicates with a Zone 1 location, it must be considered a Zone 2 location unless ventilation and safeguards are in place as per Rule 18-002 and the definition of Zone 2(b).

Rule 18-060 notes that when using metal-covered cable in hazardous locations, caution must be taken to ensure that any lightning related voltage surges on mineral-insulated cable are limited to 5 Kv, or, circulating currents on single conductor armoured cable are eliminated.

• For the former, this is accomplished using surge suppressors.

• For the latter, through bonding the metal sheaths together, at intervals of 1.8 m or less.

• Alternatively, insulation jacketed cables can be used, but the metal armour must be bonded to ground in the hazardous location and isolated in the non-hazardous location.

Rule 18-062 specifies that equipment rooms can be exempted from rules 18-100 to 18-158 if a continuous pressurized protective gas atmosphere is maintained. Appendix B has references to consult in accomplishing this. Note also that procedures must be in place to eliminate any possibility of an ignition source if pressurization fails.

Rule 18-064 specifies that intrinsically safe and non-incendive electrical equipment and wiring installed in a hazardous location

• be provided with a descriptive system document

• be installed in accordance with the descriptive system document

• be installed in a raceway, compartment, enclosure, outlet, junction box, or similar fitting, separated by a spacing of 50 mm or more, a metal armour or sheath of cable assemblies, a grounded metal barrier not less than 1.34 mm (No. 16 MSG) thick, or a non-metallic insulating material not less than 1.5 mm in thickness

• be installed in the same raceway, compartment, outlet, junction box, or multi-conductor cable where the insulated conductors of each circuit are within grounded electrically conductive shields, braids, or sheaths; or have minimum 0.25 mm thick insulation

• be installed to minimize migration of flammable fluids to other locations

• have all apparatus identified as part of the system, and

• all wiring be identified with permanently affixed labels, or

• colour coded light blue where no other cables or insulated conductors coloured light blue are used at each terminal and junction box. See Appendices B and F for additional information

Rule 18-066 requires that cable trays be open ladder type, covered or installed vertically to avoid a build-up of dust on cables.

Rule 18-068 allows that in some hazardous locations, non-hazardous, non-arcing, sparking, or heat producing equipment may be Installed where there is a detection system that continuously monitors the area and

• activates an alarm

• activates ventilation equipment, or

• de-energizes electrical equipment

if a gas concentration reaches a percentage of the lower flammable limit (LFL). The percentage depends on the existence and continued operation of a ventilation system. Refer to Appendices B and H for additional information and application.

Rule 18-070 specifies that where electrical equipment is in contact with flammable fluids, the primary seal must be constructed or installed to prevent any migration of such fluids through the wiring system. If this is accomplished using a secondary seal, an indication or warning marking is required in case the primary seal fails.

Rule 18-072 reasserts that the rules of Section 10 – Grounding and Bonding apply to hazardous locations. Additionally, where rigid metal conduit is used, threaded couplings and bosses on enclosures made up tight are required, unless incorporating internal bonding conductors.

Rule 18-074 specifies that only intrinsically safe equipment or cranes, hoists and similar equipment installed as per 18-250(2) are permitted to have uninsulated exposed parts in hazardous locations.

In the next instalment we will continue with Part B of Section 18.

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