What is the minimum ampacity required for a feeder supplying several 120-volt receptacles rated at 30A each?

To determine the minimum ampacity required for a feeder supplying several 120-volt receptacles rated at 30A each, you start by applying the relevant calculation for continuous loads. Each receptacle is rated at 30A, and if you have multiple receptacles, it’s necessary to sum their ratings for the load calculation.

If you are supplying, for example, 5 receptacles, the total load would be 5 times 30A, which equals 150A. However, according to the National Electrical Code (NEC), when calculating the feeder size, you must account for demand factors to determine the minimum ampacity.

In most cases, the NEC allows a reduction for receptacle load calculations. For example, you would typically apply a demand factor, which reduces the amount considered for the total number of receptacles. To ensure safety and to account for future loads, it’s customary to add a margin.

When you perform the calculations considering safety margins and demand factors, if you sum the receptacle loads and apply the demand factors appropriately, this leads to a required ampacity of 144 Amperes. This accounts for both the required load and safety considerations in electrical design.

Thus, the calculated minimum ampacity of 144