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NEC Calculation Requirements, Part 4

NEC Calculation Requirements, Part 4You characterize individual loads as continuous or noncontinuous. When characterizing aggregate loads, you should factor in load diversity. What does this mean? Are the NEC rules the only rules you need to follow?

The concept behind load diversity is that not all loads will operate simultaneously. To illustrate, let’s use your home as an example. How often do you run a microwave oven, hair dryer, vacuum cleaner, blender, and coffeemaker at the same time? If you had only one 20A receptacle circuit in your home, it could probably supply these loads simply due to diversity. But you could not run all of these loads simultaneously on that circuit.

In an industrial application, things are more complex but the same principle applies. A typical metal machining shop (for example, one that makes gears) has far more machines than it runs at any given time. One gear might have its keyway broached, but another needs it milled.

The challenge to the electrical designer is to accurately calculate the probability that different, specific equipment will run simultaneously. If the probability between several pieces of equipment is low, you can force load diversity by limiting the available receptacles. For two pieces of equipment, a supply scheme that uses a transfer switch can force the use of one or the other, but not both.

Avoid using operations-limiting load diversity as a way to deliver a cheap load side infrastructure. Use it to avoid having unnecessarily large service and/or load infrastructure.

« Part 3 | Part 5 » | Source: Mark Lamendola | Mindconnection