Electrical Metering Issues During Commissioning

Electricity unlike anything else is not something that can be seen, like the flow of water. Nor can it be smelt, like the breeze bringing odors. It can however certainly be felt usually with disastrous results.  As humans we rely on the five senses of sight, smell, touch, taste, hearing – electricity in general defies the ability to use most of those senses directly. We can however indirectly observe electricity through the use of meters to determine the presence of it.

Metering allows a ‘window’ in which to measure the electricity. Placement of metering devices inclusive of current and potential transformers, relays, protective devices etc. is of paramount importance as it can accurately inform the observer of what is taking place. Unfortunately, too often the accuracy of meters, of which there may be multiple meters looking at the same point, is called into question. There are many factors that need to be taken into consideration when designing a monitoring system that employs meters such as current transformer (CT) ratios, meter accuracy and  placement within equipment to name a few. If the manufacturer of say the switchgear uses CT’s and meters with an accuracy of say 2%, additional metering which may utilize different CT’s and meters at the same location with a different set of accuracies, will most likely produce conflicting results. Depending on the nature of the facility (installation) this could result in actions being taken that do not reflect what is truly occurring in the facility, more specifically the data center, among those being changes in cooling and/or shifting of loads from one Remote Power Panel / Power Distribution Units / Uninterruptible Power Supply (RPP/PDU/UPS) to another.

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