Calculate overload current from feeder load current and relay setting, or estimate load current from motor shaft power, electrical real input power or apparent power with the appropriate factors.

Current estimates and an entered load percentage only. This does not select protective devices, predict trip time or establish compliant settings.

130% means 1.3 times load, not 130% excess. Suggestions are not recommended relay settings.

Overload Current Formula

The following equation is used to calculate the Overload Current.

OLC = FLC × RS / 100
  • Where OLC is the overload current (amps)
  • FLC is the feeder load current (amps)
  • RS is the relay setting (%)

To calculate the total current at an entered load percentage, multiply feeder load current by the setting percentage divided by 100.

What is an Overload Current?

Definition:

An overload is current above normal operating or rated conditions. This calculator returns the total current corresponding to an entered percentage of feeder load, not the excess current above load.

How to Calculate Overload Current?

Example Problem:

The following example outlines the steps and information needed to calculate Overload Current.

First, determine the feeder load current. In this example, the feeder current is measured as 200 amps.

Next, determine the relay setting. The relay setting, in this case, is 130%.

Finally, calculate the overload current using the formula above:

OLC = FLC * RS/100

OLC = 200* 130/100

OLC = 260 amps

FAQ

What is the significance of calculating overload current in electrical systems?

This arithmetic ratio can support a protection study, but it cannot select circuit breakers, fuses, conductors or safe relay settings by itself. Use equipment nameplate data, manufacturer instructions and applicable requirements.

How does the relay setting affect the calculation of overload current?

The entered percentage sets the arithmetic current-to-load ratio. Actual pickup and tripping depend on relay calibration, the current transformer basis, timing, thermal behavior and coordination. A higher percentage is not automatically a suitable response to starting current.

Can overload current calculations be applied to all types of electrical circuits?

The ratio is arithmetic, but this calculator does not establish suitability for every circuit. The power mode assumes steady AC and balanced three-phase loading. Protection design must address the actual load, equipment and applicable rules.