Conductors, Cables, and Raceways

Conductors, Cables, and Cable Trays

Chapter Introduction

This chapter covers one of the most heavily tested areas on the Red Seal exam for industrial electricians: the selection, installation, and protection of conductors, cables, and cable trays. You must master the rules of the Canadian Electrical Code, Part I (CE Code) , particularly Chapters 4 (conductors), 6 (cables), and 12 (cable trays). The exam assesses your ability to apply these rules in real industrial contexts: high ambient temperatures, conductor grouping, voltage drop, and selection of installation methods.

Conductors: Types, Designations, and Applications

Conductor Classification

Conductors are classified according to their material, insulation, and temperature rating. Copper and aluminum are the two materials used in industry.

Property	Copper	Aluminum
Relative conductivity	100%	61%
Density	8.89 g/cm³	2.71 g/cm³
Tensile strength	High	Lower
Cost	High	Lower
Typical use	Circuits ≤ 500 kcmil	Circuits ≥ 1/0 AWG

Rule 4-000: The CE Code requires conductors to be copper or aluminum unless otherwise specified. In industry, aluminum is common for large sizes (motor feeders, switchgear busbars) due to its lower cost, but it requires specific connectors (anti-oxidation).

Conductor Designations (Insulation Types)

Conductors are identified by a letter code. You must know the following types for the exam:

Type	Insulation	Max Temperature	Typical Use
RW90	Cross-linked polyethylene (XLPE)	90°C dry/wet	General, industrial
TW	Polyvinyl chloride (PVC)	60°C dry/wet	Residential, light
THW	PVC	75°C dry, 60°C wet	General
THHN	Nylon/PVC	90°C dry, 75°C wet	Conduits, raceways
XHHW	XLPE	90°C dry, 75°C wet	Industrial, wet
ACWU	Aluminum armour, sheath	90°C	Buried, wet
TECK90	PVC sheath, steel armour	90°C	Industrial, wet

Exam Trap: Type THHN is rated 90°C dry but only 75°C in wet locations. If you are calculating ampacity for an outdoor conduit, you must use 75°C, even if the conductor is marked 90°C.

Temperature Rating and Ampacity

The ampacity (current-carrying capacity) of a conductor depends on:

16.The temperature rating of the insulation

17.The ambient temperature

18.The number of current-carrying conductors in the same conduit

19.The installation method (conduit, cable tray, buried)

Rule 4-004: The operating temperature of the insulation must not exceed its rated value. The CE Code tables (D1 to D5) provide base ampacities.

Temperature Correction Factor: For each deviation in ambient temperature from the reference (30°C for most tables), apply a correction factor. For example, for an RW90 conductor at 40°C ambient, the factor is 0.91 (Table 5A of the CE Code).

Calculation Formula:

Corrected ampacity = Base ampacity × Temperature factor × Grouping factor

Example: Three RW90 #2 AWG copper conductors in a conduit at 45°C ambient.

Base ampacity (Table D1): 130 A

Temperature factor at 45°C: 0.87

Grouping factor (3 conductors): 1.0 (no derating for ≤ 3 conductors)

Corrected ampacity = 130 × 0.87 × 1.0 = 113.1 A

Voltage Drop

Principles and Requirements

Voltage drop is the reduction in voltage between the source and the load, caused by the resistance and reactance of the conductors. It affects the operation of motors, lighting, and electronic equipment.

Rule 8-200: The voltage drop between the point of connection and the point of utilization must not exceed:

3% for lighting and motor circuits

5% for the total installation (service + branch circuit)

Calculation Formulas:

For a single-phase circuit:

ΔV = (2 × L × I × R) / 1000

For a three-phase circuit:

ΔV = (√3 × L × I × R) / 1000

Where:

ΔV = voltage drop in volts

L = conductor length in metres (one-way)

I = load current in amperes

R = conductor resistance in Ω/km (at service temperature)

Percentage Voltage Drop:

%ΔV = (ΔV / V_nominal) × 100

Example: Three-phase motor drawing 50 A at 208 V, supplied by a #6 AWG copper cable (R = 0.51 Ω/km) over 60 m.

ΔV = (√3 × 60 × 50 × 0.51) / 1000 = 2.65 V

%ΔV = (2.65 / 208) × 100 = 1.27% — acceptable (≤ 3%)

Exam Tip: For long runs (> 100 m), always check voltage drop BEFORE finalizing the conductor size. Table D3 of the CE Code provides maximum lengths for various conductor sizes and currents.

Industrial Cables

Armoured and Sheathed Cables

Industrial cables are assemblies of insulated conductors with a protective sheath and sometimes armour. The following types are essential:

Type	Armour	Sheath	Use
TECK90	Helical steel wire	PVC	Industrial, wet, buried
ACWU	Corrugated aluminum	PVC	Buried, outdoor
AC90	Aluminum	None (inner sheath)	Dry, indoor
NMWU	None	PVC	Buried, wet
SOW/SJOOW	None	Rubber/thermoplastic	Flexible, portable tools

Rule 12-600: TECK90 and ACWU cables may be installed:

In conduit

On cable trays

Directly buried (at the required depth)

On surfaces (with mechanical protection if necessary)

Medium-Voltage Cables (5 kV to 46 kV)

In industry, medium-voltage (MV) cables supply large motors, transformers, and internal distribution networks. Common types include:

CU/XLPE: Copper conductor, XLPE insulation

AL/XLPE: Aluminum conductor, XLPE insulation

CU/EPR: Copper conductor, EPR (ethylene-propylene) insulation

Rule 12-012: MV cables must be installed in dedicated cable trays or conduits, with adequate separation from control circuits (see Rule 12-2200 for minimum distances).

MV Cable Terminations: Terminations must be made with approved accessories (termination cones, stress cones) to control the electric field. Incorrect stripping or inadequate shield spacing causes partial discharge and failures.

Control and Instrumentation Cables

Control cables (18 AWG to 10 AWG) and instrumentation cables (thermocouples, RTDs, 4-20 mA signals) have specific requirements:

Shielding: To protect against electromagnetic interference (EMI)

Twisted pair: To reduce inductive coupling

Separation: Control cables must be separated from power cables (Rule 12-2200)

Rule 12-2200: Minimum distance of 300 mm between control/instrumentation cables and power cables in cable trays, unless a physical barrier (partition) is installed.

Cable Trays

Types and Definitions

Cable trays are continuous support systems for cables. The main types are:

Type	Description	Typical Use
Ladder cable tray	Two longitudinal rails connected by rungs	Large cables, MV
Solid-bottom cable tray	Perforated or solid plate	Control cables, small cables
Trough	U-shaped profile	Control cables
Wire mesh cable tray	Welded metal grid	Light cables, control

Rule 12-2300: Cable trays must be supported at maximum intervals of 1.5 m for ladder types and 1.2 m for solid-bottom types, unless otherwise specified by the manufacturer.

Cable Tray Fill

Fill is the percentage of the cable tray cross-sectional area occupied by cables. The limits are:

Tray Type	Power Cables (all same size)	Control Cables	Mixed
Ladder cable tray	50% of area	50% of area	Calculate per Table 12-2300
Solid bottom	40% of area	40% of area	40%

Rule 12-2302: Fill must not exceed 50% for ladder cable trays. For solid-bottom trays, the limit is 40%. These limits ensure adequate heat dissipation.

Fill Calculation:

Area occupied by cables = Σ (π × d² / 4) for each cable

Percentage fill = (Occupied area / Tray area) × 100

Example: Solid-bottom cable tray 300 mm × 100 mm (area = 30,000 mm²). Cables: 5 × TECK90 3C #4 AWG (outer diameter 28 mm).

Area per cable = π × 28² / 4 = 615.8 mm²

Total area = 5 × 615.8 = 3,079 mm²

Fill = (3,079 / 30,000) × 100 = 10.3% — acceptable

Installation and Support

Rule 12-2310: Cables in cable trays must be:

Secured at maximum intervals of 1.5 m for horizontal cables

Secured at every support for vertical cables

Protected against abrasion at penetration points

Bending Radius: The minimum bending radius for TECK90 cables is 7 × the outer diameter (Rule 12-610). For MV cables, the radius can be up to 12 × the diameter.

Exam Trap: Cables in cable trays must not be twisted or crossed. Each cable must be installed parallel to the others, without interlacing.

Conduits and Tubing

Conduit Types

Type	Abbreviation	Use
Rigid metal conduit	RMC (GRC)	Heavy industrial, outdoor
Rigid aluminum metal conduit	RMC-Al	Corrosion, reduced weight
Flexible metal conduit	FMC	Connections, vibration
Liquid-tight flexible metal conduit	LFMC	Wet, outdoor
Rigid PVC conduit	PVC	Buried, corrosion
Electrical metallic tubing	EMT	Indoor, dry
Electrical non-metallic tubing	ENT	Indoor, embedded

Rule 12-1000: The choice of conduit depends on the environment (wet, corrosive, risk of mechanical damage) and the installation method.

Conduit Fill

Conduit fill is limited to allow installation and heat dissipation. The limits are:

Number of Conductors	Maximum Fill
1	53%
2	31%
3 or more	40%

Rule 12-1014: Table 12-1014 of the CE Code provides conduit dimensions based on the number and size of conductors. You must be able to determine the minimum conduit size.

Calculation Method:

109.Determine the total conductor area (Table 6A of the CE Code)

110.Divide by the fill factor (0.40 for 3+ conductors)

111.Select the conduit whose internal area is ≥ this result

Example: 4 RW90 #2 AWG conductors (area per conductor = 92.3 mm²) in RMC conduit.

Total area = 4 × 92.3 = 369.2 mm²

Required area = 369.2 / 0.40 = 923 mm²

RMC conduit of 27 mm (internal area = 1,013 mm²) — acceptable

Maximum Length and Pulling

Rule 12-1010: The maximum length of a conduit between two pull boxes is 30 m, unless intermediate pull boxes are installed. Each 90° bend reduces the maximum length by 6 m.

Calculation: Equivalent length = Actual length + (Number of bends × 6 m)

The equivalent length must not exceed 30 m.

Example: Conduit of 20 m with 2 × 90° bends.

Equivalent length = 20 + (2 × 6) = 32 m — exceeds 30 m, a pull box must be added.

Grouping and Derating Rules

Grouping Factor

When more than 3 current-carrying conductors are installed in the same conduit or cable tray, the ampacity must be reduced. The factors are:

Number of Conductors	Derating Factor
4 to 6	0.80
7 to 9	0.70
10 to 24	0.70
25 to 42	0.60
43 and more	0.50

Rule 4-008: These factors apply to current-carrying conductors. Grounding and bonding conductors are not counted.

Exam Trap: In a three-phase circuit with a neutral, the neutral is considered current-carrying if the load is unbalanced or if the loads are non-linear (harmonics). For balanced three-phase loads (motors), the neutral is not counted.

Neutral Conductors and Harmonics

Rule 4-024: The neutral must be sized for the maximum unbalanced current. For non-linear loads (variable frequency drives, switching power supplies), the neutral can carry more current than the phase conductors due to third-order harmonics.

Requirement: For circuits with non-linear loads > 50% of the phase current, the neutral must be at least the same size as the phase conductors.

Grounding and Bonding

Grounding Conductors

Rule 10-200: The grounding conductor must be:

Copper or aluminum

Sized according to Table 16 of the CE Code (based on the size of the phase conductors)

Identified by green or green/yellow colour

Phase Conductor Size (Copper)	Minimum Grounding Conductor Size (Copper)
≤ 2 AWG	8 AWG
1 AWG to 1/0	6 AWG
2/0 to 3/0	4 AWG
4/0 to 300 kcmil	2 AWG
350 to 500 kcmil	1/0 AWG

Grounding of Cable Trays

Rule 10-402: Sections of metallic cable trays must be bonded together and grounded. Continuity must be ensured by bonding at joints and fittings.

Requirement: Each section of cable tray must be connected to the grounding conductor at maximum intervals of 30 m.

Pitfalls to Avoid

145.Confusing dry and wet temperatures: A THHN conductor is 90°C dry but 75°C wet. Always use the lower temperature for ampacity.

146.Forgetting the grouping factor: When you have 4 or more conductors in a conduit, apply the derating factor. Many candidates forget to count the neutral.

147.Not checking voltage drop: Voltage drop is often the determining factor for long runs. Always check Rule 8-200 before finalizing a conductor size.

148.Ignoring harmonics: For variable frequency drives and non-linear loads, the neutral can overheat. Size it accordingly.

149.Incorrect fill calculation: Use the total conductor area (Table 6A), not just the diameter. Remember that the fill factor depends on the number of conductors.

150.Insufficient bending radius: For armoured cables (TECK90), the minimum radius is 7 × the outer diameter. For MV cables, it is often 12 ×.

151.Confusing cable types: TECK90 (steel armour, PVC sheath) vs ACWU (corrugated aluminum armour). TECK90 is more robust and suitable for severe industrial environments.

152.Forgetting pull boxes: The equivalent length of a conduit (with bends) must not exceed 30 m. Each 90° bend counts as 6 m.

153.Incorrect conductor identification: Phase conductors must be identified by colour (black, red, blue for three-phase), the neutral by white or grey, and the ground by green or green/yellow.

154.Neglecting mechanical protection: Cables in traffic areas must be protected by conduits or mechanical guards (Rule 12-610).

Summary

Conductors: Copper and aluminum are the standard materials. Insulation types (RW90, THHN, XHHW) determine the temperature rating and use.

Ampacity: Calculate corrected ampacity by applying temperature and grouping factors. Always use the lowest temperature rating (dry vs wet).

Voltage drop: Respect the limits of 3% (circuit) and 5% (total). Use the single-phase and three-phase formulas with resistance in Ω/km.

Industrial cables: TECK90 and ACWU are the most common. Respect bending radii (7 × diameter) and installation methods.

Cable trays: Maximum fill of 50% (ladder) or 40% (solid bottom). Support at maximum 1.5 m intervals.

Conduits: 40% fill for 3 or more conductors. Maximum equivalent length of 30 m with a 6 m penalty per bend.

Grounding: Size the grounding conductor per Table 16. Bond cable trays to ground at 30 m intervals.

Key Formulas to Memorize:

ΔV three-phase = (√3 × L × I × R) / 1000

ΔV single-phase = (2 × L × I × R) / 1000

Fill = Conductor area / Conduit area

Equivalent length = Actual length + (6 m × number of bends)

Self-Assessment Questions

171.A THHN #4 AWG copper conductor is installed in an outdoor conduit (wet location). What is its maximum temperature rating?

Answer: 75°C (in wet locations, THHN is derated from 90°C to 75°C)

173.Three RW90 #2/0 AWG copper conductors in a conduit at 50°C ambient. What is the corrected ampacity?

Base ampacity: 195 A (Table D1)

Temperature factor at 50°C: 0.82

Grouping factor: 1.0 (3 conductors)

Corrected ampacity = 195 × 0.82 = 159.9 A

178.A three-phase motor drawing 75 A at 600 V is supplied by a #4 AWG copper cable (R = 0.32 Ω/km) over 150 m. Is the voltage drop acceptable?

ΔV = (√3 × 150 × 75 × 0.32) / 1000 = 6.24 V

%ΔV = (6.24 / 600) × 100 = 1.04% — acceptable (≤ 3%)

181.How many #6 AWG conductors (area = 44.7 mm²) can be installed in a 35 mm RMC conduit (internal area = 1,660 mm²)?

Maximum total area = 1,660 × 0.40 = 664 mm²

Maximum number = 664 / 44.7 = 14.8 → 14 conductors

184.A solid-bottom cable tray of 450 mm × 100 mm contains 8 TECK90 3C #2 AWG cables (outer diameter 32 mm). Is the fill acceptable?

Tray area = 450 × 100 = 45,000 mm²

Area per cable = π × 32² / 4 = 804.2 mm²

Total area = 8 × 804.2 = 6,433.6 mm²

Fill = (6,433.6 / 45,000) × 100 = 14.3% — acceptable (≤ 40%)

This chapter prepares you for Red Seal questions on conductors, cables, and cable trays. Review the CE Code tables (D1, D3, 5A, 6A, 16) and practice the calculations until they become automatic. Good luck with your preparation!