The Code is a comprehensive document. Sometimes it can seem quite daunting to quickly find the information you need. 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 2, but will hopefully provide some help in navigating the Code.
Section 4 – Conductors
The definition of Conductor, from Section 0 is: “a wire or cable, or other form of metal, installed for conveying electric current from one piece of electrical equipment to another or to ground.”
Section 4 deals with the selection of type, ampacity and installation conditions of insulated conductors. It is a general section and therefore it applies to all conductors supplying lighting, appliances and power 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. 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 wire, and cable (which are specifically covered by other Sections) is No.14 AWG 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, and the type of conductor or cable to be used.
Rule 4-004 Ampacity of wires and cables contains 7 items each in subrules (1) and (2) covering scenario options each for 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 385 calculation method or the tabulated information tables in Appendix D. The IEEE 385 Standard Power Cable Ampacity Tables contains 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: 600 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 meters 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 4-010 induced voltages and currents in metal armour or sheaths of single-conductor cables 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 Colour of 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 installments.
In the next installment, we will explore Section 6 – Services and service equipment.
* The source for this series of articles is the Canadian Electrical Code, Part I, published by CSA
1 The Canadian Electrical Code, Part I is published by the Canadian Standards Association.
2 The CEC Handbook is also published by the Canadian Standards Association