Conductor Sizes, Wiring Methods, Cable Types, Connectors, and Voltage Drop Rules

Core Canadian Electrical Code Rules for Conductors (Section 4)

• Scope of Rule 4-000: Governs conductors for electrical services, feeders, branch circuits, and photovoltaic circuits, unless specific installation requirements are provided in other dedicated sections of the Canadian Electrical Code (CEC).

• Key Governing Factors Under Section 4:

  • Conductor conditions of use.
  • Equipment termination temperature limitations.
  • Neutral conductor identification.
  • Conductor phase and circuit identification.

• Exceptions and Specialized Code Section Cross-References:

  • Motor branch circuits are governed specifically by Section 28.
  • Electric welder circuits fall under Section 42.

Conductor Sizing Systems and Construction

• American Wire Gauge (AWG) Standard:

  • Electrical conductors are sized according to the American Wire Gauge (AWG) standard.
  • Inverted Relationship: As the AWG gauge number increases, the physical cross-sectional area and diameter of the conductor decrease.
  • Size Range: Covers gauge numbers from No. 40 AWG down to No. 4/0 AWG (0000 AWG). AWG sizes 27 through 4/0 are explicitly detailed in the CEC tables.
  • "Aught" Notation Transition: Numerical gauge designations (e.g., No. 16 AWG, No. 12 AWG) transition after No. 1 AWG to "aught" numbers: No. 1/0 AWG (0), No. 2/0 AWG (00), No. 3/0 AWG (000), and No. 4/0 AWG (0000).

• Thousand Circular Mils (kcmil) Standard:

  • Sizing for conductors larger than No. 4/0 AWG transitions directly to circular mils, designated as kcmil (250\n\text{ kcmil} up to $2000\text{ kcmil}$ in the CEC).
  • Circular Mil Definition: A circular mil ($\text{cmil}$) is a unit of cross-sectional area equal to the area of a circle with a diameter of $1\text{ mil}$ ($0.001\text{ inch}$ or $\frac{1}{1000}\text{ inch}$).

• Physical Conductor Construction:

  • Conductors are manufactured as either solid wire or stranded wire.
  • Current Flow Relationship: The total current-carrying capacity increases as the physical cross-sectional area increases, allowing electrons to flow safely without exceeding thermal thresholds.
  • Rule 12-914 Requirement: Conductors sized No. 8 AWG or larger installed inside raceways must be stranded.
  • Metric Representation: In metric units, wire cross-sectional area is measured in square millimeters ($\text{mm}^2$), as cataloged in CEC Table D18 (Appendix D).
  • Material Differences: Aluminum conductors possess higher electrical resistance and lower current ampacity than copper conductors of identical cross-sectional size.

• Flexible Conductors:

  • CEC Table 12 specifies allowable ampacities for flexible insulated cords and equipment fixture wires.
  • Overcurrent Protection: Flexible conductors must be protected by fuses or circuit breakers rated no higher than the maximum ampacity of the conductor.

Electrical Wiring Hierarchy: Service, Feeder, and Branch Circuits

• Service Conductors: Conductors connecting the utility supply or line-side power source (such as transformer secondary lines) through rigid metal conduit directly to the service entrance equipment and main service disconnect.

• Feeder Conductors: Circuit conductors situated between the main service equipment and the final branch-circuit overcurrent device (e.g., non-metallic sheathed cable NMD90 running between a main panelboard and a downstream distribution subpanel).

• Branch-Circuit Conductors: The section of residential wiring extending from the final overcurrent protective device (circuit breaker or fuse) to the utilization outlet (e.g., lighting fixtures, receptacle outlets, space heaters, or stationary motors).

  • Overcurrent Device Rating: When the ampere rating of the branch-circuit overcurrent device is lower than the conductor's maximum ampacity, the overcurrent device rating dictates the formal circuit rating.

Conductor Ampacity Ratings and Correction Factors

• Ampacity Variables: The safe current-carrying capacity (ampacity) of a conductor depends on eight critical factors:

  1. Magnitude of current carried by the conductor.
  2. Ambient operating temperature.
  3. Installation environment (underground, free air, exposed aboveground, or in raceways/cables).
  4. Physical spacing between conductors.
  5. Total number of current-carrying conductors bundled or routed together.
  6. System voltage.
  7. Total circuit length/distance.
  8. Conductor physical material (copper vs. aluminum).

• Primary Installation Ampacity Classifications:

  • Single conductors installed in free air.
  • Single or multi-conductor cables and conductors in raceways.
  • Underground installations for conductor sizes $\ge 1/0\text{ AWG}$.

• Temperature Derating (CEC Table 5A):

  • Ambient air temperatures exceeding $30\,^\circ\text{C}$ require an ampacity reduction factor applied to prevent thermal breakdown of conductor insulation.

• Multi-Conductor Raceway Derating (CEC Tables 5B and 5C):

  • When more than three insulated current-carrying conductors are routed within a single raceway or bundled cable length exceeding $600\text{ mm}$, current ratings must be reduced using correction factors from CEC Tables 5B or 5C due to trapped thermal energy.

• Material Specifics in Residential Wiring:

  • All interior branch circuits in new residential construction are strictly required to be wired using copper conductors.

Temperature Ratings and Equipment Termination Requirements

• Insulation Temperature Thresholds:

  • The rated insulation temperature limits current capacities. Lower insulation temperature ratings decrease maximum allowable ampacity.
  • Comparison Example ($\text{No. 14 AWG}$ 2-conductor copper cable at $30\,^\circ\text{C}$ ambient):
  • At a $90\,^\circ\text{C}$ insulation rating, allowable ampacity is $25\text{ A}$.
  • At a $75\,^\circ\text{C}$ insulation rating, allowable ampacity drops to $20\text{ A}$.

• Bare Copper Conductors: Bare copper conductors installed in free air possess significantly higher current capacities because they are not constrained by insulation heat degradation.

• Terminal Temperature Rule (Rule 4-006):

  • When equipment termination temperature markings are not explicitly identified on electrical devices:
  • Equipment rated for $100\text{ A}$ or less: Must use the $60\,^\circ\text{C}$ ampacity column from CEC tables.
  • Equipment rated for more than $100\text{ A}$: Must use the $75\,^\circ\text{C}$ ampacity column from CEC tables.

Canadian Electrical Code Ampacity Selection (Table 4-1 Summary)

• Subrule 4-004 1) and 4-004 2) Criteria (Ambient Temperature $\le 30\,^\circ\text{C}$):

  • Single Conductor in Free Air (Spacing $\ge 100\%$ of cable diameter): Ampacity chosen from Table 1 or Table 3.
  • 1 to 3 Conductors in Raceway or Cable: Ampacity chosen from Table 2 or Table 4.
  • 4 or More Conductors in Raceway or Cable: Ampacity chosen from Table 2 or Table 4 $\times$ correction factor from Table 5C.
  • Underground Run (No. 1/0 AWG and Larger, Direct Buried or Direct-Buried Raceway, $\le 4$ Conductors):
  • Standard Configurations (Diagrams D8 to D11): Ampacity chosen from Tables D8A to D11B or IEEE 835 calculation method.
  • Non-Standard Configurations (Not in Diagrams D8 to D11): Calculated via IEEE 835 calculation method.
  • Underground Run (Smaller than No. 1/0 AWG, Direct Buried or Direct-Buried Raceway, $\le 4$ Conductors):
  • Calculated via IEEE 835 method or specified directly in Tables 2 and 4.

• Subrule 4-004 8): Single conductor in free air with spacing between $25\%$ and $100\%$ of largest cable diameter uses Table 1 or Table 3 $\times$ correction factor from Table 5D.

• Subrule 4-004 9): Not more than 4 single conductors in free air with spacing less than $25\%$ of largest cable diameter uses Table 1 or Table 3 $\times$ correction factor from Table 5B.

• Subrule 4-004 11): 5 or more single conductors in free air with spacing less than $25\%$ of largest cable diameter uses Table 2 or Table 4 $\times$ correction factor from Table 5C.

Insulation Types, Cable Classifications, and Applications

• Conditions of Use Selection (CEC Table 19):

  • Table 19 dictates where conductor types are legally permitted based on environment:
  • Locations: Dry, damp, or wet.
  • System Use: Consumer's service, feeders, branch circuits, control/instrumentation, Class 2 circuits, fire alarm circuits.
  • Installation Methods: Exposed, concealed, raceways, cable trays, direct burial, exposed to sunlight, plenums, outdoor overhead.

• Conductor Insulation Letter Codes:

  • R: Thermoset insulation (e.g., R90, RW90).
  • T: Thermoplastic insulation (e.g., T90, TW90).

• Residential Cable Classifications:

  • NM (Non-Metallic Sheathed Cable): Designated as NMD90 for 2-conductor non-metallic dry-type interior applications.
  • AC (Flexible Armored Cable): Designated as AC90 (commonly known as BX).
  • LVT (Extra Low Voltage): 5-conductor signal/thermostat wiring.
  • TECK90 (Flexible Armored Weatherproof Cable): PVC-jacketed armored cable for damp, wet, and direct burial locations.
  • FAS (Fire Alarm Signal Cable): 2-conductor fire alarm cable featuring solid core No. 14 AWG copper conductors with FLPR-rated PVC jacketing.
  • SJ (Junior Service Cord): Flexible 3-conductor service cord rated at $300\text{ V}$.
  • US: Underground Service Entrance Cable.
  • NS: Neutral Supported Overhead Cable.

Residential Conductor Application Requirements (Table 5-1 & Table 5-7)

• Minimum Conductor Size: The minimum conductor size permitted for general wiring in single-dwelling residential construction is No. 14 AWG.

  • Code Exceptions: Covered under Section 16 and CEC Table 12 for internal luminaire wiring, doorbell wiring, and remote-control low-energy circuits.

• Application Table Summary (Table 5-1):

  • No. 18 AWG, No. 16 AWG: Flexible cords, extra-low voltage control circuits, doorbell and chime wiring.
  • No. 14 AWG, No. 12 AWG: General residential lighting branch circuits, circuits supplying general-purpose receptacle outlets.
  • No. 10 AWG, No. 8 AWG, No. 6 AWG, No. 4 AWG: Dedicated heavy appliance branch circuits (clothes dryers, electric ovens, ranges, cooktops, electric water heaters, heat pumps, central air conditioning units, electric furnaces) and subpanel feeders.
  • No. 3 AWG, No. 2 AWG, No. 1 AWG (and larger): Main electrical service entrance conductors, main feeders to distribution panels and subpanels.

• Comparative Uses of NMD90 vs. NMWU (Table 5-7):

Voltage Drop Sizing and Calculations (CEC Rule 8-102)

• Principles of Voltage Drop: Conductor resistance converts electrical energy into heat, causing reduced line voltage at the utilization load. Excessive voltage drop causes light flickering/dimming, motor overheating, and inefficient appliance performance.

• Mandatory Limits (CEC Rule 8-102):

  • Branch Circuits Only (Rule 8-102 1) a)): Voltage drop must not exceed $3\%$ from the overcurrent panel to the farthest load outlet.
  • Combined Feeder + Branch Circuit (Rule 8-102 1) b)): Total voltage drop from the supply service to the farthest outlet on a branch circuit must not exceed $5\%$

• Voltage Drop Calculation Examples ($120.0\text{ V}$ Base System):
  • Maximum Branch Circuit Drop ($3\%$):       $\text{Voltage Drop} = 120.0\text{ V} \times 0.03 = 3.6\text{ V}$$\text{Minimum Load Voltage} = 120.0\text{ V} - 3.6\text{ V} = 116.4\text{ V}$
  • Maximum Total Combined System Drop ($5\%$):       $\text{Voltage Drop} = 120.0\text{ V} \times 0.05 = 6.0\text{ V}$$\text{Minimum Load Voltage} = 120.0\text{ V} - 6.0\text{ V} = 114.0\text{ V}$

• Feeder and Branch Distribution Splits:
  • If feeder voltage drop is $3\%$, maximum branch circuit voltage drop is $2\%$.
  • If feeder voltage drop is $2\%$, maximum branch circuit voltage drop is $3\%$.
  • Requirement: A connected load must be actively operating across the circuit to establish a measurable voltage drop.
  • Calculation Tables: Calculations are performed using CEC Table D3.

Solderless Wire Connectors and Splice Terminations

• Wire Connector Types and Specifications:
  • Crimp Connectors: Used for splicing and terminating No. 20 AWG to $500\text{ kcmil}$ aluminum-to-aluminum, aluminum-to-copper, or copper-to-copper conductors. Requires proper mechanical crimping followed by electrical tape insulation.
  • Twist-On Solderless/Tapeless Connectors: Connect wire combinations ranging from No. 18 AWG through No. 6 AWG. Includes trademarked models Wire-Nut, Wing-Nut, Marrette, and Twister (registered trademarks of Ideal Industries, Inc.), as well as Scotchlok (registered trademark of 3M).
  • Crimp-Type Connectors with Insulating Caps: Used for combining No. 16 AWG, No. 14 AWG, and No. 12 AWG conductors. Crimped using a specialized crimping tool and enclosed with a protective snap-on insulating cap.
  • Solderless Lugs / Pressure Terminals: Ranging in size from No. 4 AWG through $500\text{ kcmil}$. Rated for one solid or one stranded conductor (unless otherwise stated). Feature standard slotted screws or Allen/socket wrench tightening mechanisms.
  • Compression Connectors: Sized from No. 8 AWG through $1000\text{ kcmil}$. The stripped conductor is inserted into the barrel and crimped with a rated compression tool.
  • Split-Bolt Connectors: Sized from No. 10 AWG through $1000\text{ kcmil}$. Designed for joining two conductors together or tapping a branch conductor onto a continuous main line. Accepts two solid and/or stranded conductors.

Non-Metallic-Sheathed Cable (NMSC) Installation Guidelines

• Structural Support and Fastening (Rules 12-550 to 12-576):

• Maximum Distance Between Cable Straps or Staples: Must not exceed $1.5\text{ m}$.
• Maximum Distance from Box to First Strap/Staple: Must not exceed $300\text{ mm}$.
• Box Securing: Cable must be secured within $300\text{ mm}$ of non-metallic outlet boxes, with an approved cable clamp applied.
• Sheath Visibility: Non-metallic outer jacket sheath must extend into the box and be visible inside the box after installation.
• Conductor Free Length: Leave at least $150\text{ mm}$ of free conductor measured from the point where the conductor enters the box.
• Orientation Requirement (Rule 12-556 6)): Flat 2-wire non-metallic sheathed cables must be stapled flat against wooden framing. It is prohibited to staple 2-wire NMSC on edge. Approved staple sizes include S1, S2, and S3.

• Physical Protection Standards:
  • Floor Penetrations (Rule 12-906):

- Exposed NMSC passing through a floor must be encased inside rigid PVC conduit or another approved raceway extending at least $1.5\text{ m}$ above the floor line.
- Cable must be protected against sheath abrasion at both open ends of the conduit sleeve.

• Framing Member Edges (Rule 12-564):

- Cables run parallel to floor joists or wall studs must maintain a clearance of at least $32\text{ mm}$ from the nearest edge of the wooden framing member.
- If the $32\text{ mm}$ clearance cannot be maintained, a steel metal protection plate must be installed over the face of the member.

• Metal Stud Installation:

- Approved plastic bushings or snap-in grommets must be inserted into steel stud knockout holes before routing NMSC to prevent metal edges from cutting the cable sheath.

• Unfinished Basement Joists (Rule 12-564 1) b)):

- Cables of any size may be run along the sides or face of joists, or threaded through bored holes in joists.
- Running cables directly across the bottom exposed edges of joists without protective guard strips is prohibited unless protected from injury.

• Cold Air Return Passages (Rule 12-010 5)):

- NMSC is permitted to pass through cold air return stud or joist spaces in single-dwelling residences provided the cable passes straight through at right angles to the long dimension of the space.
- Routing cables longitudinally inside cold air ducts, or mounting outlet/junction boxes within air plenums, is strictly prohibited.

• Cable Derating for Bundling:
  • When multiple cables are bundled together for distances exceeding $600\text{ mm}$, the ampacity correction factors in CEC Table 5C must be applied. Penetration holes through framing must be fire-stopped/draft-stopped with thermal insulation, caulk, or sealing foam.

Raceway Systems, Conduit Types, and Flexible Fittings

• Rigid and Flexible Metal Conduit: Governed by CEC Rules 12-1000 through 12-1014.

• Electrical Metallic Tubing (EMT): Governed by CEC Rules 12-1400 through 12-1414.

• Rigid Polyvinyl Chloride Conduit (PVC): Governed by CEC Rules 12-1100 through 12-1124.

• Electrical Non-Metallic Tubing (ENT): Governed by CEC Rules 12-1500 through 12-1514.

• Flexible Metal Conduit (FMC): Governed by CEC Rules 12-1000 through 12-1014 and Rules 12-1300 through 12-1308.

• Flexible Conduit Classifications:

• (A) Flexible Metal Conduit (FMC): Standard spirally wound metallic armor for dry, protected locations.

• (B) Liquidtight Flexible Metal Conduit (LFMC): Metallic core covered with an outer liquidtight plastic jacket (e.g., Liquatite Type LA).

• (C) Liquidtight Flexible Non-Metallic Conduit (LFNC): Non-metallic smooth or corrugated jacketed conduit (e.g., Liquatite Type LNM-P).

  • Raceway Fittings:

• Group A: Straight and 90-degree squeeze-clamp fittings for FMC.
• Group B: Liquidtight compression fittings and 90-degree connectors for LFMC.
• Group C: Liquidtight non-metallic screw-on/compression connectors for LFNC.