2018 Canadian Electrical Code Changes – Resistor Monitoring
In 2018, the Canadian Electrical Code (C22.1-18) introduced measures in section 10-302 to ensure that all neutral grounding resistors are continuously monitored for open and short conditions, something commonly referred to as “Resistor Monitoring”.
Here is an excerpt of the section:
The integrity of an impedance grounded system shall be monitored, and the system shall have an audible or visual alarm that corresponds to the occurrence of
- a ground fault on current-carrying conductors, including the neutral conductor where line-to neutral loads are served;
- a ground fault on the conductor connecting the impedance grounding device to the source; and
- a loss of continuity of the impedance grounding circuit from the system source through the impedance grounding device to the grounded non-current-carrying conductive parts of the electrical system.
Most NGR monitoring relays on the market are compliant with the open circuit detection requirement, but only two relays are compliant with the short circuit requirement.
A sensing resistor or coupling device is normally used to monitor the neutral path to ensure the NGR is not in an open condition. When a short condition is present, the NGR path has a parallel path. As a result, the sensing resistor current still has a full path, even though the NGR is in a short condition. This can result in a false sense of safety. If a ground fault were to happen, the resistor would fail and the ground fault would be uncontrolled, causing the destruction of equipment and potential injury or death to personnel.
As a user or customer of NGRs, you must be aware which ground fault relays support short condition monitoring and which do not.
The method of short circuit detection deployed by the i-Gard Sigma is based on measuring the leakage current present in the system, as described by i-Gard documentation in the SIGMA manual.
In a balanced power system under normal operating conditions, there is little to no leakage current present and as such, the Sigma would fail to detect short circuits reliably. The Sigma cannot be relied upon to trip in a shorted-NGR condition, as required by the Code. This may also cause false trips, which may leave systems out of service temporarily when there is no true fault.
The SE-325 requires the use of a sensing resistor to detect open circuit NGR’s but does not have any capability to monitor for short circuits.
The RC48N requires the use of a coupling device to detect open circuit NGR’s but does not have any capability to monitor short circuits.