280 Electrical Power Systems Technology
FEEDER CIRCUIT DESIGN CONSIDERATIONS
Feeder circuits are used to distribute electrical power to power distri-
bution panels. Many feeder circuits extend for very long distances; there-
fore, voltage drop must be considered in feeder circuit design. In higher
voltage feeder circuits, the voltage drop is reduced. However, many lower
voltage feeder circuits require large-diameter conductors to provide a tol-
erable level of voltage drop. High-current feeder circuits also present a
problem in terms of the massive overload protection that is sometimes re-
quired. This protection is usually provided by system switchgear or load
centers where the feeder circuits originate.
Determining the Size of Feeder Circuits
The amount of current that a feeder circuit must be designed to carry
depends upon the actual load demanded by the branch circuit power dis-
tribution panels that it supplies. Each power distribution panel will have
a separate feeder circuit. Also, each feeder circuit must have its own over-
load protection.
The following problem is an example of size calculation for a feeder
circuit.
Sample Problem:
Given: three 15-kW fluorescent lighting units are connected to a
three-phase, four-wire (277/480-volt) system. The lighting units have a
power factor of 0.8.
Figure 10-10. Diagram of a three-phase circuit breaker