Station ground work • Code File, December 2019
January 30, 2020 | By Kavita Sabharwal-Chomiuk
When designing a station, there are numerous issues which must be addressed at the design stage and carried through to the installation. Some of the questions the authority having jurisdiction (AHJ) may ask include: What is the soil resistivity? What is the possible Ground Rise Potential (GPR) for this location? How will the station be accessed? How will a safe touch and step potential be maintained? How will we alert persons of the possible hazards in and around the site?
As an inspector, we often run into some of these issues which have not been addressed adequately, during or after construction. This can be an expensive time to modify or change the design to meet CE Code requirements. Early questions and follow-up can assist in these concerns being addressed at the design stage, which saves time and money on the ground.
In preparation for the grounding of a High Voltage Station, a determination of the system’s needs must first be reviewed. One question that sometimes catches designers off guard is the request for a GPR study. This may be requested for installations, such as in mining where it is required by the CSA M421 standard, but may be required for other locations as well.
The rules which I have personally found in violation are as follows:
No signage mounted on the gates. While it seems like a good idea when the gates are closed, once the gates swing open, they are no longer visible to persons passing by. Section 36-006 (1)(e) states that for this reason, signage should be located adjacent to the gate locks, on all access gates, at all outside corners, and at intervals not exceeding 15 m.
Gate direction must be considered. The CE Code states in 26-310 that the gates shall open outward whenever possible. This outward swing also causes designers to miss the requirement of 36-312 which states the fence shall be located at least 1 m inside the station ground electrode area. If the gates, which are a part of the fence, swing outward, then at their outermost point, they must still be 1 m within the grounding electrode area, which means the electrode area must extend beyond just the confines of the fence.
The ground cover must extend far enough. Section 36-304 (5) requires that where the safety of persons depends on the presence of a ground surface covering layer, it shall extend throughout the station grounding electrode area, as well as 1 m beyond it on all sides. This means that if the grounding electrode area is 1 m beyond the fence, then at a minimum, the ground surface covering layer must be 2 m beyond the fence (shown as grey in the diagram).
The use of standard copper wire 2/0 for the whip to the gate. Section 36-312 (3) states that the connection shall be a copper braid or flexible copper conductor. Contractors do not want to go back two years after construction to replace a copper jumper which is now broken because it was not flexible enough.
Be sure to talk to your local AHJ prior to construction starting to be sure you have all of these and any other concerns addressed by the early stages of construction.
David Pilon is an electrical inspector with SaskPower, the utility’s training co-ordinator for electrical inspectors and vice-chair of the Canadian Certified Electrical Inspector (CCEI) committee of the International Association of Electrical Inspectors (IAEI), Canadian section. He can be reached at email@example.com.
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