Most of the time, we tend to rely exclusively on the Canadian Electrical Code for information, and for the minimum requirements on building a safe electrical installation. But is the information contained between its covers enough for our purposes – or do we need to look further afield to find out more? Are there any other sources of information we should explore to grasp the complete picture?
Let’s consider one prime example where the electrical code does not give us all of the information we need to make a safe installation. Our example – a high voltage padmount transformer (over 750 volts primary voltage) must only be supplied from a grounded electrical distribution system that brings a primary neutral conductor into the substation. This is imperative in the event of a ground fault, since we want all of ground fault current to return to its source through a low impedance path. Hazardous step and touch potentials near the transformer can result when there is no neutral and when the ground fault return path is through the earth. We must provide the lowest possible impedance fault path to make sure that any faults in equipment or cabling are disconnected promptly by the upstream ground fault protection equipment.
You will recall that step voltage is the voltage between your feet when walking or standing near high voltage electrical equipment during a ground fault. Touch voltage is the voltage between your hands and your feet when you touch electrical equipment during a ground fault. Both are the result of ground current flow x the impedance of the current return path (Ohm’s Law).
Safety in a padmount transformer installation is surely most important, since we know that padmount transformers are not usually enclosed by fences and are often accessible to the public. We will not find this important bit of information in the Canadian Electrical Code – because it’s not there. But rather, we must turn to the CSA padmount transformer standards, CAN/CSA-C227.3-M91(R1997) for single-phase transformers or C227.4-M1978(R1994) for three-phase transformers to access this information. But you will find these requirements in the very first paragraph, the Scope paragraph in each standard, which describes the conditions of use for this type of equipment.
There are many more examples. As we peruse the Canadian Electrical Code, we find that not all of its requirements are to be found between it covers. There is an abundance of requirements and/or additional information necessary for doing a complete design or installation job. Here are a few more examples.
1. A footnote under Table 31 – Minimum Horizontal Separations of Line Conductors Attached to the Same Supporting Structure states: “For voltages greater than 69 kV and for spans greater than 50 m, the requirements of CSA Standard CAN/CSA-C22.3 No.1 shall apply.” Note the words shall apply. That means, of course, that when we design or build an overhead line to be used at above 69 kV phase-to-phase or any line when the pole spans are greater than 50 metres, the code does not have this information and we must turn to that standard for the requirements on clearances.
2. Rule 12-012(12) Underground Installations states: “For installations not covered by the foregoing requirements of this Rule, the requirement of CSA Standard C22.3 No.7, or the applicable standard, whichever is greater shall apply. That tells us, when the installation falls outside the scope of requirements covered by the electrical code, we must consult the appropriate CSA standard.
3. Rule 36-304(2) Station Ground Resistance refers us to Table 52 and Appendix B for information and data on the maximum permissible step and touch voltages in a high voltage substation. We must have this information to design the station ground grid in such a way that these values will not be exceeded. When we turn to Table 52 and Appendix B, we find that we must also have access to another standard, IEEE No. 80 Guide for Safety in Substation Grounding to find the formulae to perform these calculations. Fortunately, there are a number of available software programs based on the standard, to perform this arduous task more easily.
4. Fire pumps – Rules 32-200 to 32-212 provide the basic electrical code requirements for fire pumps. However, the code does not give us the complete information on overcurrent protection, etc. Therefore, Appendix B refers us to NFPA Standard No. 20 Standard for the Installation of Centrifugal Fire Pumps for the rest of the information.
These are only a few of many documents, which the Canadian Electrical Code refers us to for additional requirements or further information. Where can we find a list of these publications? Go to pages 32 to 34 in the 1998 Canadian Electrical Code. There you will find a list of the publications referenced in the rules as requirements or available for more information. At the bottom of the list you will also find a listing of the organizations that produced these publications.
As mentioned in previous articles, you should consult your local inspection authority for a more precise interpretation of any of the above, in each province or territory as applicable.