Customer requirement is shown below:

  • Current Limiting Reactor (CLR), 57 Amps continuous, 400 Hz, P/N 18786L
  • Rating: 480 VAC, 1 PH, 400 Hz, 57 amps continuous
  • Fault current: 1030 Amps
  • Inductance L (1, 2) = 107 uH ± 25%, see calculation below
  • 15 VAC drop is estimated across the CLR at 57 amps continuous current.
  • When 57 amps increase momentarily to a catastrophic fault condition to 1030 A, CLR develops 277 VAC across it. Eventually, the circuit breaker will trip and inhibit the fault condition.  Details are provided with calculations below.
  • RDC = 0.00155 ohms
  • Calculated core loss: 27.5 watts
  • Calculated copper loss: 5 watts
  • Temperature rise: 35 degrees C
  • Forced air cooling is required.
  • Open core and coil: 5″H x 5″W x 5″D
  • Copper bus bar: ⅛” x ⅝” with a hole
  • Core is gapped.  Without gap, core will saturate at 15 VAC voltage drop. With gap, the core will saturate at voltages higher than 15 VAC.
  • Three P/N 18786L are required for one system

The photo of the CLR is shown below:

Based on the customer application, the inductance value is calculated as follows:

  • Assuming 15 volts drop across the Current Limiting Reactor at 57 amps
  • V = 2 x π x f x L x I (continuous current)
  • L = V / (2 x π x f x I)
  • L =  15 / (2 x 3.142 x 400 x 57) = 107 uH

The fault current condition calculation is shown below.  It is assumed that the fault voltage of 277 VAC is developed across the CLR under worst case conditions. Customer to approve our approach and methodology.

  • Assuming 277 volts drop across the Current Limiting Reactor as worst case fault voltage, the fault current is estimated at 1030 amps
  • V = 2 x π x f x L x I (fault current)
  • I = V / (2 x π x f x L)
  • I = 277 / (2 x 3.142 x 400 x 107 uH) = 1030 Amps

The voltage drop across the CLR at different current level is shown in the table A below:

 The customer application is shown below:

  The photo of three CLR’s is shown below:


L/C Magnetics can build current limiting reactors from as low as 57 amps to as high as 10000 amps per customer requirements. These units are brand new concepts and built to order. Customer feedback is important to us to continually improve and optimize these units. To discuss your specific application, please call us toll free at (800) 595-7096, or send us an email at

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