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Panelboards: What to Know About Load Calculations

Updated: Dec 8, 2021

Utilizing load calculations within Revit gives us a more accurate summary of how much power is to be provided. Revit uses load classifications to assign specific demand factors to the desired powered device. As we go through our design it is not enough to simply power a device to a panel. Calculations, for example, are based on NEC (National Electrical Code) Articles 220 and 620 for elevators, to determine the demand factors.

How do we calculate load in Revit?

  • You can assign the demand factor to be based on the number of connected objects. For example, table 220.56 in the NEC indicates demand factors for kitchen equipment. For the first two units, all loads are calculated at 100%. If there are six units or more, then all loads are calculated at 65%.

  • You can apply a constant demand factor to the loads regardless of their values. A constant demand factor is the default for any newly created demand factor, and the default calculation method if a demand factor is not specified for a load classification.

  • This is where you can set up different classifications for loads. For example, click to see if you have an elevator. If so, you will see equipment and a demand factor in the dialog box. Each piece of equipment lists a demand factor. As you go through, each will show whether it is constant and what the demand factor is. You can look at it by constant, by quantity or by load.

  • Total connected load = the sum of all loads attached to the panel (directly or to subpanels) from connectors specified as part of that load classification group.

  • Demand Load = the sum of the demand loads for each load classification for connectors specified as part of the load classification group.

How did the panelboard schedules look before?

Our old way of showing loads in our Revit panelboard schedules didn’t provide enough information to give an accurate panelboard load summary and rating of the panelboard itself that directly related to the NEC requirements. Our new way of showing the total demand and total connected load in our panelboard schedule load summary is better, more efficient, and accurate. Additionally, it allows us to provide the calculations directly on the drawings for review by local AHJ’s (Authorities Having Jurisdiction) with the need for additional documentation.

Written by:

Samantha Oliver

Electrical Design Engineer


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