Grounding & Bonding Systems
Grounding electrode conductors, ground rods, bonding to water pipes, neutral-to-ground bonds, sub-panel isolation, and equipment bonding.
- Explain the purpose of grounding and bonding in residential electrical systems
- Describe grounding electrode requirements including ground rods
- Identify bonding requirements for water pipes and gas piping
- Explain the neutral-to-ground bond at the main panel
- Describe sub-panel grounding and neutral isolation requirements
Lesson 1
Grounding Electrodes & Ground Rods
Purpose of Grounding
The grounding system in a residential electrical installation serves two critical purposes: it provides a path for fault current to flow back to the source (enabling overcurrent devices to trip) and it stabilizes voltage levels relative to earth. Without proper grounding, metal enclosures, pipes, and structural steel could become energized during a fault - creating a lethal shock hazard.
Grounding Electrode Types
The OESC recognizes several types of grounding electrodes:
- Ground rods - copper-clad steel rods driven into the earth
- Metal water pipe - at least 3 m of buried metallic water pipe in contact with earth
- Concrete-encased electrode (Ufer ground) - reinforcing steel in a concrete foundation
- Ground plate - buried metal plate with minimum area in contact with earth
Ground Rod Installation
A ground rod must be:
- At least 3.0 metres (10 feet) long
- At least 15.8 mm (5/8 inch) in diameter
- Driven vertically into the earth to its full length
- Connected to the grounding electrode conductor with an approved clamp
Exam Tip
If a single ground rod does not achieve 25 ohms or less resistance to earth, a second rod must be installed at least 3 m away from the first. Two rods together are accepted without further testing.
Grounding Electrode Conductor (GEC)
The grounding electrode conductor connects the main panel's grounding bus to the grounding electrode (ground rod or water pipe). The GEC must be:
- Copper (most common) or aluminum
- Sized per OESC Table 17 based on the service conductor size
- Protected from physical damage where exposed
- Connected without splices (or with irreversible compression connectors)
Ground rods must be at least 3.0 m long and 15.8 mm diameter. If a single rod exceeds 25 ohms resistance, a second rod is required at least 3 m away. The grounding electrode conductor connects the panel to the grounding electrode.