Point of Common Coupling
Point of Common Coupling
Point of Common Coupling
Review:
Tech Notes Date: 2015
Page: 1 of 1
PCC within the plant and between the non-linear and linear loads
Considering the PCC at the equipment will often meet the IEEE-limits both at this point and also at a PCC near the
service entrance. The IEEE-519 limit at this point, which is essentially at the input to the non-linear loads, is often
12%, 15% or even 20% THD-I. The ratio of short circuit current to load current is typically much larger at this PCC,
which typically has less total load, than at the metering point, where the entire plant load is connected. Usually, if
the THD limit is met at each non-linear load within the plant, the TDD limits at the service entrance will also be
met. Even though the THD limits are typically lower for the PCC considered near the utility metering point, the
overall THD at this PCC may be considerably lower if there are additional linear loads in the plant that share the
power source.
When the point of common coupling (PCC) is considered at the service entrance or utility metering point, IEEE-519
recommends that the maximum demand load current (IL) be calculated as the average current of the maximum
demand for the preceding 12 months. To calculate TDD for new construction, prior to installation of equipment,
one may use good engineering judgments to estimate the expected maximum demand load current. A conservative
approach is to use the summation of the FLA ratings of all motors and other loads as the maximum demand load
current.