Naturally, customers are concerned about the cost of correcting existing situations. Making the call on how far to go in requiring existing installations to be improved must be handled on a case-by-case basis. Clear communication of the proposed changes and improvements and the interests of all involved is a great place to start. No commitments need to be made at this point, as the meeting is strictly to gather information for further study before plans are drawn. The question is, how do you handle the inspection of a new installation or an existing medium voltage system that is being modified? How far do you go to bring the work up to Code? A field visit to the site by the electrical inspector, along with the customer, engineer, contractor, and supplying utility representatives may be in order. Most jurisdictions and their inspection staff will face this situation eventually. Permanent and conspicuous warning signs per 110.34(C) If this is the case, the new owner has the choice of repairing the existing system or installing a new medium voltage system. On the other hand, adverse changes to the electrical system may have come about by walls, fences or structures being built that impinge on working clearance, accidental damage to the installation, deterioration by weather or lack of maintenance, or by an unsafe modification of the original installation. If the installation is unaltered, it is often permitted to remain as is by inspection authorities unless someone notices a severe hazard, because it was installed by qualified persons and generally with engineering supervision. In most cases, the installation was completed many years, if not decades, earlier and was designed under utility engineering supervision and not required to meet any requirements of the NECat the time. Locked electrical rooms or enclosuresĮxisting electric utility installations often vary widely from the NEC. Code-compliance is required per NEC 90.2(A) when a new system is installed or when an existing system taken over from the utility is altered or upgraded.įigure 1. The customer becomes responsible for all upkeep and repairs of the equipment, conductors, poles, and structures. This saves the utility labor and material costs. Reduced power rates are made available via primary metering, which is when the electric utility sells the utility-owned medium voltage power system on the customer’s property to the customer, meters the power at a higher voltage and reduced rate, and is no longer responsible for maintenance of the equipment. As all businesses seek to operate more efficiently and cut costs, incentives may be offered to large power users who own the entire electrical distribution system on their property, including all power distribution systems operating at over 600 volts. As with many changes, cost savings are a factor. Prior to that, with few exceptions, electric utilities owned these systems. In the past 20–30 years, there has been a proliferation of customer-owned medium voltage distribution systems in North America. Many industrial plants, universities, medical facilities, and high-rise buildings are served by medium voltage electrical distribution systems. Medium voltage switchgear (motor control center) Code sections and basic requirements will be provided for a typical scenario of a customer-owned system consisting of a service disconnect on the property, an underground feeder to a primary transformer, and underground raceways and cables installed into switchgear or a unit substation. It is not comprehensive but rather a guide to assist those who may be new to inspecting medium voltage installations up to 15,000 volts. This article will be useful as a start to the education process. High voltage is defined by NEC 490.2 as any system operating at “more than 600 volts, nominal.”įield electrical inspectors may be asked to inspect medium voltage installations in the course of their duties, but some may feel unqualified or overwhelmed at the thought of inspecting these installations because their work experience has been more residential and commercial construction, and they have little or no medium voltage experience. Medium voltage systems are defined by the IEEE as those operating at voltage levels greater than 1,000 volts and up to 72,000 volts.
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