Grounding and Bonding

Introduction

Grounding and bonding are among the fundamental pillars of electrical safety. For the Red Seal exam, you must master not only the theoretical concepts but also the precise requirements of the Canadian Electrical Code, Part I (CE Code) (24th edition). This chapter typically represents 10 to 15% of exam questions. A misunderstanding here can lead to multiple failures, as these concepts cut across nearly every other area of the trade.

This chapter covers essential definitions, physical principles, calculation rules, installation procedures, and the typical traps that candidates encounter.

Fundamental Definitions

Grounding

Grounding is the intentional electrical connection of an electrical system, equipment, or raceway to the earth (ground) via a low-impedance path. Its primary purpose is to limit the voltage between conductors and the earth to safe values and to provide a return path for fault currents.

Bonding

Bonding is the electrical connection of all non-current-carrying metal parts (masses) to maintain them at the same electrical potential. It does not necessarily pass through the earth — it connects the masses to each other and to the grounding conductor.

Crucial Distinction

Characteristic	Grounding	Bonding
Primary purpose	Limit voltage to earth	Equalize potentials between masses
Path	To earth (electrode)	Between metal masses
Conductor	Grounding conductor	Bonding conductor
CE Code reference	Rules 10-000 to 10-600	Rules 10-200 to 10-302

Never confuse these two concepts. Grounding protects against overvoltages and enables the operation of protective devices. Bonding protects people against electric shock by eliminating dangerous potential differences.

Other Key Definitions

Grounding electrode: a conductive element buried in direct contact with the earth (rod, plate, buried conductor).

Grounding conductor: the conductor connecting the electrode to the distribution panel or system.

Bonding conductor: a conductor connecting two metal masses or a mass to the grounding conductor.

Mass (exposed conductive surface): a conductive part of equipment that is not normally energized but could become energized under fault conditions (motor frame, metal enclosure, etc.).

Earth (ground): the mass of the planet, considered an infinite reservoir of electrical charge.

Physical and Electrical Principles

Why Ground?

22.Voltage limitation: in the event of a fault between an energized conductor and a mass, grounding limits the potential rise of the mass to a safe level.

23.Protective device operation: sufficient fault current must flow to operate the circuit breaker or fuse. Without grounding, an insulation fault might go undetected.

24.Potential stabilization: the earth serves as the zero-potential reference for the entire system.

25.Lightning and surge protection: surge protective devices (SPDs) only work if they are properly grounded.

Ground Resistance

The total resistance of a grounding system is the sum of:

The resistance of the grounding conductor (negligible in practice)

The contact resistance between the electrode and the soil

The resistance of the soil itself

Soil resistance varies greatly depending on:

Moisture: dry soil has much higher resistivity

Temperature: frost increases resistivity

Chemical composition: salt and conductive minerals reduce resistivity

Depth: the deeper the electrode, the lower the resistance

Target value: the CE Code recommends a ground resistance of 25 Ω or less for a single electrode (Rule 10-500). In practice, for sensitive installations (IT, medical), 5 Ω or less is often targeted.

Typical Soil Resistivity

Soil Type	Resistivity (Ω·m)
Marshy, wet	5 – 30
Clay	30 – 100
Moist sand	100 – 300
Gravel	300 – 1000
Rock	1000 – 10 000
Dry sand	10 000 – 100 000

Canadian Electrical Code Requirements

Rule 10-200: Grounding of Systems

Every electrical system must be grounded, except as otherwise provided (e.g., extra-low-voltage safety systems, certain isolated systems for medical applications). Grounding must be done at a single point, generally at the main distribution panel.

Rule 10-204: Grounding Conductor

The grounding conductor must:

Be copper or aluminum

Have a minimum size according to Table 16 of the CE Code (see table below)

Be continuous, without splices (except by exothermic connection or certified connectors)

Be mechanically protected where exposed to damage

Table 16: Minimum Size of Grounding Conductor

Phase Conductor Size (copper, mm²)	Minimum Grounding Conductor Size (copper, mm²)
≤ 2.5	1.5
4 – 6	2.5
10 – 16	4
25 – 35	6
50 – 70	10
95 – 120	16
150 – 185	25
240 – 300	35
400 – 500	50
600 – 800	70

Note: For aluminum, use Table 16B of the CE Code. In general, the aluminum grounding conductor must be larger than copper for the same capacity.

Rule 10-300: Grounding Electrodes

Electrodes accepted by the CE Code are:

53.Ground rod: copper or copper-clad steel rod, at least 3 m in length, driven vertically (Rule 10-302)

54.Ground plate: metal plate of at least 0.2 m² surface area, buried at least 600 mm deep

55.Buried conductor: bare conductor at least 6 m in length, buried at least 600 mm deep

56.Concrete foundations: steel reinforcing bars embedded in concrete in contact with the soil (concrete-encased electrode)

57.Metal water pipe: potable water piping buried for at least 3 m (Rule 10-400)

Additional electrode requirement: if the resistance of the main electrode exceeds 25 Ω, an additional electrode must be installed (Rule 10-500).

Rule 10-400: Bonding of Metal Raceways and Piping

All metal piping (water, gas, heating, etc.) entering a building must be bonded to the grounding conductor. This bonding must be done at the building entrance, before any meter or isolation valve.

Caution: The gas piping must be bonded but must NOT be used as a grounding electrode (Rule 10-402). This is a distinction the exam frequently tests.

Rule 10-600: Bonding of Masses

All non-current-carrying metal masses in a building must be bonded together and to the grounding conductor. This includes:

Metal device boxes

Cable trays and metal raceways

Building steel structures

Metal enclosures of motors and transformers

Metal conduit

Calculations and Sizing

Maximum Fault Current Calculation

The maximum fault current (short-circuit current) is determined by:

System voltage

Source impedance (transformer)

Conductor impedance

Fault path impedance

Simplified formula:

I_fault = U / (Z_source + Z_conductors)

Where:

U = phase-to-ground voltage (V)

Z = impedance (Ω)

Fault Loop Verification

For a circuit breaker to trip, the fault current must exceed the magnetic trip current (typically 5 to 10 times the rated current). The total resistance of the fault loop must be sufficiently low.

Practical example:

A 120 V circuit protected by a 15 A breaker with magnetic trip at 10× (150 A).

Maximum loop resistance: R = 120 V / 150 A = 0.8 Ω

If the loop resistance exceeds 0.8 Ω, the breaker will not trip quickly enough — this is a real danger.

Maximum Conductor Length Calculation

For a conductor of cross-section S (mm²), the resistance is:

R = ρ × L / S

Where:

ρ = resistivity of copper = 0.0172 Ω·mm²/m (at 20 °C)

L = total circuit length (out and return) in meters

S = cross-section in mm²

Example: 2.5 mm² conductor, 30 m circuit (60 m out and return):

R = 0.0172 × 60 / 2.5 = 0.413 Ω

Resistance Table by Length (copper)

Cross-section (mm²)	Resistance per meter (out and return) at 20 °C (Ω/m)
1.5	0.0229
2.5	0.0138
4	0.0086
6	0.0057
10	0.0034
16	0.0022
25	0.0014
35	0.0010

Installation Procedures

Installing a Ground Rod

100.Site verification: ensure no underground utilities are present (prior location is mandatory)

101.Driving: the rod must be driven vertically to full depth (3 m minimum) using a hammer drill or mechanical equipment

102.Connection: the grounding conductor is attached to the rod using a certified connector (compression or bolted type)

103.Protection: the connection must be protected against corrosion and mechanical damage (sleeve, protective box)

104.Measurement: verify the ground resistance with a ground resistance tester (earth tester)

Critical point: The connector between the grounding conductor and the rod must be visible and accessible (Rule 10-302). It must never be buried directly.

Bonding a Bathroom

According to Rule 10-700, all metal masses in a bathroom (piping, bathtub, shower frame, etc.) must be bonded together. This bonding is typically done with a minimum 4 mm² conductor.

Measuring Ground Resistance

The ground resistance tester (earth tester) uses the 3-point method:

110.Place the ground rod to be tested (X)

111.Place a voltage probe (Y) at 62% of the total distance

112.Place a current probe (Z) at the total distance (at least 30 m)

113.Inject current between X and Z, measure voltage between X and Y

114.R = U / I

Exam trap: The distance between probes must be at least 30 m to obtain a reliable measurement. Too short a distance gives a falsely low reading.

Grounding Systems by Installation Type

TN System (grounded neutral)

The source neutral is grounded

Masses are connected to the protective conductor (PE) which is connected to the neutral

Sub-types: TN-C (neutral and PE combined), TN-S (neutral and PE separate), TN-C-S (combined then separated)

TT System (independent grounding)

The source neutral is grounded

Masses are grounded via an independent electrode

Requires a mandatory residual current device (RCD)

IT System (isolated neutral)

The source neutral is isolated from earth or grounded via high impedance

Masses are grounded

Used in critical environments (hospitals, continuous-process industries)

System Comparison

Characteristic	TN	TT	IT
Neutral to earth	Yes, directly	Yes, directly	No, isolated or via impedance
Masses to earth	Via PE	Independent electrode	Independent electrode
Mandatory protection	Breaker/fuse	RCD mandatory	RCD + insulation monitoring
Service continuity	Low	Medium	High
Typical use	Residential, commercial	Agricultural, construction sites	Hospitals, industries

Note: The CE Code requires the neutral to be grounded at the service point (Rule 10-200). TT and IT systems are less common in North America, but you must know them for the exam.

Supplementary Bonding

In Wet Locations

Bathrooms, pools, saunas, and laundry areas require supplementary bonding (Rules 10-700 to 10-702). All accessible metal masses must be bonded together, even if they are already individually grounded.

In Swimming Pools

Rule 10-702 requires:

Bonding of all metal masses within a 3 m radius of the pool

Minimum 4 mm² bonding conductor

Pool concrete reinforcing must be bonded

In Medical Facilities

Operating rooms and intensive care areas require IT systems with insulation monitoring (Rule 10-1000). Bonding must be particularly rigorous to prevent any micro-shock.

Traps to Avoid

144.Confusing grounding and bonding: these are two distinct concepts with different functions. Grounding connects to earth; bonding connects masses to each other.

145.Using gas piping as an electrode: this is prohibited (Rule 10-402). Gas piping must be bonded but never used as an electrode.

146.Forgetting the additional electrode: if resistance exceeds 25 Ω, a second electrode is mandatory (Rule 10-500).

147.Burying a ground rod connector: the connector must be accessible for inspection and measurement.

148.Neglecting bonding conductor size: the bonding conductor must have a minimum cross-section of 4 mm² for most applications, and never smaller than the grounding conductor.

149.Believing the earth is a return conductor: the earth must never be used as a normal current return path. It is only for fault conditions.

150.Forgetting to bond metal piping: all piping (water, gas, heating, air conditioning) must be bonded at the building entrance.

151.Ignoring the 62% rule: for earth tester measurements, the 62% distance is essential for accurate readings.

152.Confusing Tables 16 and 16B: Table 16 applies to copper, Table 16B to aluminum. The sizes are not identical.

153.Not verifying bonding continuity: a loose or corroded bond is as dangerous as no bond at all.

Exam Tips

Memorize key values: 25 Ω (max resistance), 3 m (rod length), 600 mm (burial depth), 4 mm² (minimum bonding).

Learn Table 16: questions on minimum conductor sizes are frequent.

Visualize the diagrams: mentally draw fault paths for each system type (TN, TT, IT).

Read questions carefully: the Red Seal exam often uses wording that tests the distinction between grounding and bonding.

Practice fault loop calculations: knowing how to determine whether a breaker will trip is a tested skill.

Know the exceptions: for example, extra-low-voltage systems (≤ 30 V) are exempt from grounding under certain conditions.

Summary

Concept	Key Point
Grounding	Connection to earth to limit voltages and enable protective device operation
Bonding	Connection of masses to each other to equalize potentials
Electrode	3 m rod, plate, buried conductor, foundation, water pipe
Max resistance	25 Ω (single electrode), additional electrode if exceeded
Table 16	Minimum grounding conductor sizes in copper based on phase sizes
Gas piping	Bonding mandatory, but never as an electrode
Measurement	Earth tester, 3-point method, 62% distance
Bathrooms	Supplementary bonding mandatory (Rule 10-700)
TN/TT/IT systems	Different grounding schemes with specific protections
Rod connector	Always accessible, never buried

Mastering grounding and bonding is essential not only for passing the exam but also for practicing the trade safely. These rules protect lives — yours and those of end users. Deepen your understanding of every CE Code rule mentioned in this chapter, and practice with sample questions to consolidate your knowledge.

Grounding and Bonding