Current Shunt

A shunt is a calibrated resistor of a known value, which is connected in series within an electrical circuit.  By measuring the voltage across the shunt , the magnitude of current flowing within the circuit can be calculated.

A shunt is a calibrated resistor with a known value.  In cathodic protection, shunts are used for many applications.  Some uses include:

  • Measure the current output of an anode (galvanic or impressed current)
  • Verify the accuracy of rectifier panel mounted ammeters
  • Measure the current in pipeline resistance bond connections

The primary advantage of having a shunt in a circuit is to measure the current flow without disconnecting the circuit to install a portable ammeter.

Shunts come in many sizes and ratings ranging from less than one ampere to thousands of amperes with varying resistance values.  With the proper shunt in a circuit, you can determine the magnitude of current flow by using a typical digital multimeter.


Holloway Type JB

This is a 0.01 ohm, 8A ampere capacity manganin strip shunt designed for use in junction boxes. Size is 1/2″ x 3-3/4″. Standard hole size is for #10 (3/16″) screws. Optional hole size for 1/4″ screws is available. Hole spacing is 3-1/4″.

Holloway Type RS

This 0.01 ohm shunt is rated at 6 amps and is made from #12 manganin wire. With a overall length of 5-3/4″, the shunt can be bent to fit into small areas. The RS shunt is used for junction boxes, test stations and similar applications.

Holloway Type SO

This is a 0.001 ohm shunt is rated at 50 amps and is constructed of #4 manganin wire and 1/4″ x 1/2″ x 1-1/8″ brass end plates for mounting. Mounting holes in the brass plates are made for 1/4″-20 screws and are on 3-3/8″ centers. 10-32 screws are provided for permanent lead connections.

Holloway Type SS

This is a 0.001 ohm shunt is rated at 25 amps and is constructed of copper nickel alloy ribbon. Provided mounting holes are on 2-3/4″ centers for a 3/8″ bolt.10-32 screws are provided for permanent lead connections.

Type SW

The type SW shunt is available in a number of current ratings from 5 to 200 amps and is constructed of manganin ribbon with brass end plates. Mounting holes vary with the shunt rating.

Cott- Shunt

This shunts are popular in post-mounted test stations.  They are color-coded to depict their resistance value.

Red = 0.1 Ω

Yellow = 0.01 Ω

Orange = 0.001 Ω

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