The Canadian Electrical Code Part I gives electrical utilities an exemption from the code for “installations and equipment in its exercise as a utility, located outdoors or in buildings or sections of buildings used for that purpose.” The CEC Part I is “a voluntary code for adoption and enforcement by regulatory authorities.” When adopted into the provincial regulations, this exemption is almost always maintained for work that falls within the scope of an electrical utility’s business.
Over time, many electrical utilities have either developed their own design standards or use standards developed by others. Two CSA standards are often used as authoritative references for utility installations. These are CAN/CSA-C22.3 No. 1- M87 Overhead Systems and C22.3 No. 7-94 Underground Systems. In some instances, utility standards may meet or exceed electrical code requirements, or they may also fall short. One would hope that utility standards should satisfy minimum electrical safety requirements, especially for installations on private property.
In a brave new world of less regulation and greater competition, electrical utilities may want to take a closer look at their own design standards, to determine whether they should conform with the Canadian Electrical Code. In this article, we will look at some examples where the CEC Part III standards fail to meet the minimum safety requirements of the CEC Part I, and visit another issue that might affect electrical utilities as changes evolve.
Let’s begin by comparing some of the differences in high low and high voltage clearances. I will refer to the Canadian Electrical Code as CEC Part I and the CSA Part III overhead standards as CEC Part III. Both prescribe minimum horizontal and vertical clearances for a broad range of voltage classifications. As an aside, there are a few instances where the CEC Part I actually references CEC Part III when an installation strays beyond the parameters set out in the code. As a result, some paragraphs of CEC Part III actually become requirements of our electrical code.
For our first example, CEC Part I specifies a minimum vertical clearance of 4.0 m for low voltage service conductors across a residential driveway. This increases to 5.0 m when crossing the driveway to a commercial or industrial facility. Using the same example, CEC Part III would require minimum clearances of 3.7 m for low voltage service conductors across a residential driveway, and 4.42 m crossing the driveway to a commercial or industrial facility. Obviously, there is some disparity between the two standards.
CEC Part I specifies a minimum vertical outdoor clearance of 7.0 m for 46 kV exposed live parts such as cable terminations, fuseholders and switches, located outside a substation fence. CEC Part III has different requirements for areas accessible only to pedestrians and where there is also access by vehicles. The comparable 46 kV CEC Part III clearances would be:
- 3.7 m – where accessible only to pedestrians
- 5.2 m – where also accessible to vehicles
Here there appears to be a major difference between these standards for the elevation of high voltage exposed live parts.
Horizontal clearances between power lines and buildings is another place where there are differences. CEC Part I, requires a minimum 3 m horizontal distance between 46 kV lines and buildings (still far too close in this writer’s opinion). However, CEC Part III goes even further. Here the minimum horizontal distance between 46 kV lines and buildings is 1.0 m plus conductor swing to “a normally inaccessible surface” and 1.8 m plus conductor swing to a “readily accessible surface.”
The CEC Part III definition of readily accessible is “that an object is accessible to persons without the use of special means” (for example, a ladder). The amount of conductor swing depends upon whether the line is considered to be sheltered from the wind. In the writer’s opinion, the horizontal clearances in both CEC Part I and Part III are both deficient. However the CEC Part III requirements have a greater potential for problems and electrical accidents.
A further requirement of CEC Part I is calculating the 5000-volt maximum ground potential rise, and the step and touch voltages in substations. These are determined from the ground electrode resistance and the available ground-fault current. The first step normally involves ground resistivity measurement, then calculating the maximum step and touch potentials as specified in Table 52 of CEC Part I. Parameters for these calculations are found in the IEEE No. 80 substation grounding standard.
Ground potential rise can be calculated from station ground resistance and the available ground-fault current. Some electrical utilities are more interested in minimizing ground potential rise, since the GPR may affect any communications equipment installed in stations. Step and touch potentials have also been identified as a safety issue and therefore should be considered as well.
For the reasons mentioned, electrical utility installations should comply with the Canadian Electrical Code Part I, particularly on customers’ property. As with previous articles, you should consult the electrical inspection authority in each province or territory as applicable, for a more precise interpretation of any of the above.