D2 - LT4 - CEC Section 10 Grounding and Bonding Flashcards
What are the objectives of grounding and bonding?
Protect from electric shock
Limit voltage under lightening strike
Prevent property damage
Limit voltage to 150 volts to ground
Facilitate operation of overcurrent protective devices
What is system ground?
The grounding of the neutral connector to ensure the electrical ground is the same value as the earth ground surrounding it.
Prevents voltage-to-ground from rising above a safe value due to a fault outside the building.
Grounding resistance must be made as low as possible.
What is Equipment bond?
The bonding of exposed conductive materials such as conduit, switch boxes, and meter frames, which enclose conductors and equipment.
Prevents electric shock to persons coming into contact with any metallic object which, either intentionally or accidentally, form part of the electrical system.
How do you ensure you have an effective equipment bond?
Rule 10-600
Ensure all couplings and connector set screws are mechanically tight
Ensure bonding jumpers are installed (if required)
Ensure bonding screws and locknuts are tightened
You may have to scrape paint/finishes around knockouts to ensure that locknut teeth are firmly in contact with bare metal
Where should the ground be connected?
Rule 10-204(1)(a)
The grounded connector (or neutral) must be grounded at the source of supply, at the first point where the neutral is broken.
Why must all bonding straps or screws be removed from all panels downstream from the main service?
Rule 10-204(1)(c)
If the neutral connector is connected to a ground downstream of the service box, it will then become a bonding conductor as well as a neutral conductor, carrying normal load current.
Bonding paths should only carry current as a result of short circuits. they aren’t designed to carry current continuously. The result would be hotspots and sparks.
Why must non-electrical metal equipment in buildings be bonded to ground?
Rule 10-406
Electrical wiring can fault to metal parts in buildings causing arcing or electric shock.
Items like Metal Gas Pipes, Continuous Metal Waste Water Pipes, Metal Water Pipes must be bonded to ground.
What are acceptable ways to ensure good bonding connections are made to the system ground?
Rule 10-618(1)(a)
It is acceptable to use the metal raceways as the bonding path
Ensure conduit work is secure and locknuts are tightened well
Where raceways are not considered good enough (Flexible metal conduits), bonding conductors are installed within the raceway itself.
Bonding jumpers from bond bushings can be installed but must be sized according to rule 10-614(1)
What are the three choices for grounding electrodes?
Rule 10-700
as per subrule (1)
- Manufactured electrodes, such as rods or plates
- Field-assembled electrodes, such as Ufer ground
- In-situ electrodes, forming part of an existing installation
How can you install manufactured electrodes - RODS?
Rule 10-700
As per subrule (2)
When using rods, two are installed at least 3m apart, each being 3m long
The system ground would then be attached to either rod.
What happens when something prevents you from installing grounding rods at their full length?
Rule 10-700
subrule (5)
a lesser depth is acceptable if rocks or permafrost prevents you from installing a grounding rod 3m deep.
However, the grounding rod must not be cut.
A 600mm trench in line with the grounding rod should be dug and the rod should be bent in its place
How can you install manufactured electrodes - PLATE ELECTRODE?
Rule 10-700
Subrule (2)(b)
Dig a hole 600mm deep and insert the plate electrode for connection to the system ground.
How can you install manufactured electrodes - Ufer GROUND?
Rule 10-700
This method of grounding was developed during WWII as a cost-effective means to ground in very dry, desert conditions.
Subrule (3)
A bare copper conductor, 6m in length, is installed within a concrete footing.
The concrete footing must be in direct contact with the earth and at least 600mm below grade.
How can you install manufactured electrodes IN-SITU GROUNDING ELECTRODE?
Rule 10-700
Subrule (4)
the system ground can be attached to something provided by the existing building infrastructure as long as the items are 600mm below grade and extend at least 3m
ex.
metal water piping system
rebar found in a concrete grade slab
iron piling
metal well casing
What is the grounding conductor size for AC systems?
Rule 10-812
the min. system ground conductor must be #6 AWG copper or #4 AWG Aluminum.
In most electrical services, this will be smaller that the size of the service neutral.
