Current clamp

This allows measurement of the current in a conductor without the need to make physical contact with it, or to disconnect it for insertion through the probe.

A common form of current clamp comprises a split ring made of ferrite or soft iron.

In the iron vane type, the magnetic flux in the core directly affects a moving iron vane, allowing both AC and DC to be measured, and gives a true root mean square (RMS) value for non-sinusoidal AC waveforms.

The Hall effect type is more sensitive and is able to measure both DC and AC,[1] in some examples up to the kilohertz (thousands of hertz) range.

It has the advantage of better linearity, having no core to saturate, it can be made flexible, and does not require any magnetic or electrical contact at the opening end.

[2] The Rogowski coil gives a voltage proportional to the rate of change of current in the primary cable, so more signal processing is needed before the sensed values can be displayed.

This could be clamped around standard two- or three-conductor single-phase cables to provide a readout of the current flowing through the load,[3] with no need to separate the conductors.

The Columbia tong test ammeter (illustrated) is an example of the iron vane type, used for measuring large AC currents up to 1000 amperes.

Interchangeable meter movements can be installed in the clamping assembly to provide various full-scale current values up to 1000 amperes.

Several jaw sizes are available for clamping around large conductors and bus bars up to 4+1⁄2 inches (110 mm) wide.