A feeder in a single-family dwelling supplies a load of 75 A of electrical space heating and 25 A of air conditioning. The required capacity of the feeder is _____ amps?

To determine the required capacity of the feeder for a single-family dwelling supplying an electrical space heating load of 75 A and an air conditioning load of 25 A, it's essential to understand how to calculate the total demand on the feeder.

For electric space heating, the full load amperage is typically used in the calculation, which is 75 A. However, as per the National Electrical Code (NEC) guidelines regarding air conditioning, you can apply a demand factor to the air conditioning load. The NEC allows a reduction in the air conditioning load for feeders. In most cases, only half of the air conditioning load is considered for demand calculations, leading to an additional 12.5 A (25 A / 2).

Adding these two components together gives you:

• Full load for heating: 75 A

• Demand for air conditioning: 12.5 A (half of 25 A)

When you sum these, the total demand on the feeder becomes 75 A + 12.5 A = 87.5 A.

According to the sizing rules, it is common practice to round up to the nearest available standard size for feeders. In this instance, the nearest standard size over 87.5 A is 90