NEC Calculation Requirements, Part 13

NEC Calculation Requirements, Part 13Previously, we discussed the few ways Article 215 affects your calculations. But we didn’t discuss the fact that it’s often difficult to tell if you actually have an Article 215 application.

In a simple layout, it’s not an issue. For example, your service switchgear is near the service entrance, which is supplied by the utility’s 480V transformer. You run feeder cable or feeder bus at 480V from the service switchgear to stepdown transformers and to distribution panels that supply utilization equipment voltages such as 277V for lighting and 120V for receptacles.

But what if you have 480V motor loads? Are these feeders or branch circuits? We’ll answer that shortly.

What if you have onsite generation with no serving utility? Are the conductors from the generators service conductors or feeders? Answer: they are feeders.

Let’s look at what Article 100 says about a branch circuit to see about answering that motor question. A branch circuit consists of “The circuit conductors between the final overcurrent  device protecting the circuit and the outlet(s).”

But isn’t a motor a load rather than an “outlet?”

We’ll have to see what Article 100 says about a feeder circuit then. It consists of “All between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.”

As in real estate, location is everything. Look at where the OCPD is relative to the load and you’ll know whether you have a feeder or branch-circuit.

« Part 12 | Part 14 » | Source: Mark Lamendola | Mindconnection

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