- Safety Corner | June 13, 2017
Focus on Your Customer With an Eye on Safety
Customer wants and needs all too often get forgotten as we get too obsessed with meeting National Electrical Code (NEC) requirements. We need to be as obsessed about meeting our customer wants and needs as we are with meeting what, in reality, is a bare minimum for electrical safety. It may shock you to learn that a system designed to meet the minimum requirements of the NEC may not be adequate for the application. This article will discuss a few key areas where your design may need to exceed the bare minimum requirements of the NEC.
The electrical inspecting community must have a mindset of being “Inspectors” and not “Expectors” when it comes to reviewing an installation with the NEC in mind. This refers to the fact that they look at a system as it is designed and installed. They are not there to look into the future with regard to how the system may or may not change with time. On the other hand, the designer must put on the hat of the “Expector” to ensure the demands of the installation and the customer are met over time.
Section 90.1 tells us that the purpose of this Code is the practical safeguarding of persons and property from the hazards arising from the use of electricity. This section includes a sentence that says, “This Code is not intended as a design specification or an instruction manual for untrained persons.” A little further we find
90.1(B), which speaks to adequacy. We are reminded here that the NEC contains requirements necessary for safety and that compliance will give you a system free from hazard but not necessarily one that is efficient, convenient, or adequate.
The following are some areas where your customers’ wants and needs may exceed the bare minimum for safety. Use these as a stimulus to your own thoughts in other areas not addressed here.
The infrastructure of the electrical system is not something that is changed often. When we size distribution transformers, panelboards, switchgear, switchboards, and service entrance equipment, they will be there for a very long time and will face changes that will place more or less demands on the power distribution system. We arrive at the size of such equipment as services, conductors, and transformers based upon our load calculations found in Article 220. A quick glance at Section 220.12, titled “Lighting Load for Specified Occupancies,” shows us an informational note that says, “The unit values are based on minimum load conditions and 100 percent power factor and may not provide sufficient capacity for the installation contemplated.” Once we have selected conductors and transformers and electrical equipment and have them installed, expanding capacity when we have designed the system with narrow or no margin may be quite expensive. We can’t say that the NEC didn’t warn us.
A short-circuit calculation considers the impedances of a system as well as all fault contributors. Popular key contributors to short-circuit current include the utility feed, motors, and generators on site. Popular reducers of short-circuit current include conductors, transformers, inductors, and busway. Changes in the power distribution system can impact the available short-circuit current. For example, adding motors can increase available short-circuit currents seen in the power distribution system. Changing impedance contributors in the system, such as transformers, can have significant impact to the available short-circuit current. We use calculated short-circuit currents when we select such equipment as circuit breakers, fuses, and other types of