Nov 6, 2019

By William (Bill) Burr

Often, code users encounter situations where they find themselves at odds with the rules contained in the Canadian Electrical Code, Part I. These situations can occur for designers, consultants, installers, inspectors, manufacturers, students, instructors and standards developers alike, and these situations usually are a result of a misreading, misunderstanding, misapplication or inability to locate the requirement that is needed or that is relevant to their tasks. The Code is a comprehensive document. Sometimes, it can seem quite daunting to quickly find the information you need. Over the next 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 4 — Conductors

The definition of Conductor, from Section 0 is: a conductive material that is constructed for the purpose of carrying electric current and includes:

• Bare Conductor — a conductor having no covering or insulation

• Covered conductor — a conductor covered with a dielectric material no rated dielectric strength

• Insulated conductor — a conductor covered with a dielectric material having a rated dielectric strength (note that a dielectric material conducts practically no current due to polarization)

Section 4 deals with the determination of maximum allowable conductor ampacity, maximum conductor termination temperature, selection of a neutral conductor, conductor type for a specific condition of use and conductor identification.

It is a general section and therefore it applies to all conductors for services, feeders, branch circuits, and photovoltaic circuits. The selection of other conductors, such as for control, grounding, emergency, safety, fire alarms, airport installations, renewable energy, communications, cathodic protection, and others, will be governed by individual sections covering these situations. Appendix B notes that branch circuits include lighting, appliance, power supply circuits, flexible cords and equipment wires are covered by Section 4.

Individual sections such as: Section 6 – Services and service equipment, Section 8 – Circuit loading and demand factors, Section 10 – Grounding and bonding, Section 12 – Wiring methods, Section 14 – Protection and control, Section 16 – Class I and Class II circuits, and Section 26 – Installation of electrical equipment; may also apply as general sections, or may have rules that reference or amend Section 4.

For this reason, it is important to compare the rules in Section 4 with the rules governing conductors in the section dealing with your particular installation. For instance, Rule 4-002 requires that the minimum size for all copper conductors, except for flexible cord, equipment wire, or control circuit insulated conductors and cable, and insulated conductors (which are specifically covered by other Sections) is No.14 AWG copper and No. 12 AWG if, aluminum. However, in Section 6, Rule 6-302 – Installation of overhead consumer’s service conductors requires that the minimum size for overhead consumer’s service conductors is No.10 AWG copper or No. 8 AWG aluminum. Even though there are amendatory sections and rules later in the Code, it is still very important that you refer to Section 4, first, when selecting and installing any conductor.

When selecting a conductor, there are several factors to be considered. Because of the complexity of conditions, you need to have a process to determine the correct type and size for your application. The first consideration is to choose the size of conductor you need based on

• the current it will be required to carry

• the conditions under which it will be installed

• the type of conductor or cable to be used

Rule 4-004 Ampacity of wires and cables contains 7 items in each of subrules (1) and (2) covering scenario options for each of copper and aluminum that need to be studied and chosen. In addition, there are 21 other factors in the subsequent subrules that need to be considered. Although this may seem daunting at first, it is simply a matter of going through the list of options and conditions and choosing the ones that apply to your situation. Rule 4-004 will then direct you to the correct table and correction factor for your situation. In some cases, you will be directed to use the IEEE 835 calculation method or the tabulated information tables in Appendix D. The IEEE 835 Standard Power Cable Ampacity Tables — https://standards.ieee.org/standard/835-1994.html —contain all pertinent equations and has the electrical/thermal analog circuit and calculation examples in the annex.

Once the right ampacity has been chosen or calculated, the next factor to consider, per Rule 4-006, is the temperature limitations on the conductor ampacity you have chosen. Where the maximum conductor termination temperature is marked on the equipment, you will have already chosen the minimum size of conductor based on the correct temperature column of Tables 1, 2, 3 or 4. Where the maximum conductor termination temperature is not marked on the equipment, the temperature to be used is:

• 60 0 C for equipment rated 100 A or less or marked for use with No.1 AWG or smaller conductors, or

• 750 C for equipment rated more than 100 A or marked for use with conductors larger than No. 1 AWG

It should also be noted that these conditions only apply to the first 1.2 metres of conductor length, measured from the termination point of the equipment.

One other condition to note is, when using a single conductor cable with a metal sheath or armour that, induced voltages may cause the conductor insulation temperature to exceed its rating. In this case Rule 4-008 – Induced voltages and currents in metal armour or sheaths of single-conductor cables and single insulated conductor requires you to derate the conductor along with some other procedures to mitigate this situation.

The next important consideration outlined in Rules 4-008, 4-012, 4-014, 4-016, 4-018, 4-020, 4-040 and 4-042 is the selection of the type of insulated conductor, flexible cord, equipment wire or portable power cable. In some cases, these rules will specify minimum sizes and ampacities for the various types.

Finally, we go back to Rules 4-022, 4-024, 4-026, 4-028, 4-030, 4-032, 4-034, and 4-036 which provide for the use of a common neutral, installation, identification and use of neutral and identified conductors. Rule 4-038 Identification of insulated conductors covers the colouring of insulated grounding and bonding conductors, and where colour-coded circuits are required.

You will note that Section 4 does not apply to non-insulated grounding or bonding conductors. The use, size and ampacity of these conductors is covered by Section 10, which we will deal with in subsequent instalments.

In the next instalment, we will explore Section 6 — Services and service equipment.

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.