By William Burr

Since ground fault circuit protection was adopted in Canada over 40 years ago, the number of people dying annually from electrocution has been steadily reduced from over 800 to less than 200, and much electrical equipment and other infrastructure has been saved from damage (source: Electrical Safety Foundation International ESFI). The following overview outlines how ground fault detection and protection ensures the safety of personnel and equipment.

The Canadian Electrical Code* defines a “ground” as a connection to earth obtained by a grounding electrode, and a “ground fault” as an unintended electrical path between a part, operating at some potential to ground, and ground. The code requires ground fault current to be detected, and in most cases requires electrical equipment to be protected from a ground fault by interrupting the undesirable fault current.

A ground fault circuit interrupter (GFCI) breaks the fault current. The GFCI is designed to open the circuit, or a portion of the circuit to a load, within a predetermined value. This value must be less than the current level required to operate the overcurrent protective device of the circuit.

 Where the GFCI is required to provide protection for personnel, the level must be above 4 milliamperes but not more than 6 milliamperes and must operate within a time-frame of less than 25 milliseconds. This is defined as a “Class A ground fault circuit interrupter” (Class A GFCI). It is also designed to open the circuit to the load if the neutral conductor is inadvertently grounded between the interrupter and the load. Note that the function of the Class A GFCI is to provide protection against hazardous electric shocks from leakage current flowing to ground. It does not provide protection against shock if a person makes contact with two of the circuit conductors on the load side of the GFCI.

 Where the GFCI is for the protection of equipment only, the current interrupting level is set at a level high enough to protect the equipment from damage, but less than the level required to operate the overcurrent device protecting the circuit. In some instances, where equipment must run continuously, and there is minimal hazard to personnel, a “ground fault detector” may be used. This device detects a ground fault and provides an indication or alarm, that a ground fault has been detected. It does not necessarily control or interrupt the ground fault and so is not considered ground fault protection. It does alert qualified maintenance staff to investigate and correct the fault. These devices are mostly used for poly-phase ungrounded systems, neutral grounding devices, and industrial machinery.

 The most widespread use of the Class A GFCI is for receptacles located near water or the earth. The Canadian Electrical Code requires that a Class A GFCI be provided to protect all receptacles within 1.5 metres of a sink. In addition, in residential occupancies the code requires that all receptacles installed outdoors and within 2.5 metres of finished grade be protected by a Class A GFCI. An exception is automobile heater receptacles that have been installed as per the provision of Rule 8-400 of the code for parking stalls in parking lots.

 In the case of swimming pools, which includes hydro massage bathtubs, spas and hot tubs, wading pools, baptismal pools, decorative pools, and splash pads, all receptacles located between 1.5 metres and 3 metres of the inside walls of the pool and receptacles located in change rooms associated with a pool must be protected with a Class A GFCI. All electrical equipment located within the confines of the pool or within 3 metres of the walls, spas and hot tubs, and audio amplifiers connected to speakers in the pool water must also be protected with a Class A GFCI. Where a Class A GFCI is not available, due to rating, the equipment may be protected with a GFCI that will clear a fault within the time and current values of a Class A GFCI.

Solidly grounded systems rated more than 150 volts to ground, less than 750 volts phase to phase and 1000 amps or more; and rated 150 volts or less to ground and 2000 amperes or more, are required to have ground fault protection that de-energizes all normally ungrounded conductors of a faulted circuit that are downstream from the main disconnect. This ground fault protection can be incorporated in the over current device, a separate tripping system consisting of sensors, relays and auxiliary tripping mechanism or other means that will provide the necessary protection.

 For more comprehensive information, refer to the Canadian Electrical Code, Part I.

* References to the Canadian Electrical Code or the Code are to the Canadian Electrical Code, Part I, Twenty-second edition, published by the Canadian Standards Association

 William (Bill) Burr is the former Chair of the Canadian Advisory Council on Electrical Safety (CACES), former Director of Electrical and Elevator Safety for the Province of BC, and former Director of Electrical and Gas Standards Development and former Director of Conformity Assessment at CSA Group. Bill can be reached at Burr and Associates Consulting billburr@gmail.com.