NEC Concepts: the Importance of the Total Electrical Load
With review ongoing to implement NEC 2020's changes, as construction professionals we can not lose sight of the NEC's basics. In this newsletter, we look at one of these "basics": the importance of the results of Total Electrical Load calculations being accurate.
At PowerCalc, our approach is to calculate loads from the branch circuit to the service entrance (bottom-up. This approach mirrors the NEC's framework and our "founding" electricals knew a few things about electricity. In Article 2 "Wiring and Protection", the NEC's requirements move from design of the Branch Circuit out to the facility's service entrance reflecting a "bottom / up" approach.
Why is this important? There should never be an error in the Total Electrical Load for any project. And yet, the miscalculation of the Total Electrical Load is one of the most common mistakes in electrical engineering design.
The proper, and only fail-proof way to do an electrical design, is to add all the electrical loads from the circuit out to the service entrance and then updates for changes are made across the entire design both upstream and downstream (bottom-up approach). This is the same approach indicated in the very structure of the NEC. Ideally, the load downstream should automatically carry over to all upstream panelboards, constantly updating the electrical load.
In comparison, guesstimating the size of the electrical load in conjunction with pre-sets of panelboard sizes, transformers, equipment disconnects, feeders and overcurrent protection devices at the start of the project may lead to an inaccurate baseline on which to build the electrical engineering design.
This is construction, so changes are the standard in our business. As all construction professionals know equipment is added and deleted, building layouts changed, room sizes increased and decreased…the one constant is that everything affecting the electrical engineering design is always changing.
How could anyone know the size of the electrical service at the start of a project? No one can guesstimate the Total Electrical Load in conjunction with the factors identified above at project start. But by following the structure of the NEC, that is adding all the electrical loads from the circuit out to the service entrance, the professional can correctly size and adjust for changes in the electrical load for the project. This is the methodology automated by PowerCalc and an important reason for the exacting accuracy in its calculations and design of the power distribution system.
Why is this so important? And what is the outcome of an addition or subtraction mistake? Electrical equipment is either oversized at potentially great cost to the developer or undersized at potentially great risk to safety (fire) for those occupying the building.
So, the Total Electrical Load drives the success of your electrical engineering design.
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Look forward to working with you.