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Current Relay

Last updated: September 3, 2019

What Does Current Relay Mean?

A current relay is a type of electromagnetic switch used as part of the control systems for electrical equipment. These relays are commonly used as sensors (current sensor/monitoring relays) to monitor current flow within industrial and other safety-sensitive equipment. Such equipment utilizes current relays to prevent malfunctions due to excessive or insufficient amounts of electrical current (“overcurrent” and “undercurrent,” respectively).

If too much current flows through a machine equipped with a current relay, the relay will activate, switching off or otherwise altering the amount of energy allowed to flow through the circuit or circuits the relay is connected to. This lowers the amount of current that's allowed to move through the system. The same functionality can be provided to machines or other electrical apparatuses to prevent damage due to undercurrent.

Current relays can be used for both AC and DC set-ups, and their ability to prevent equipment failures due to overcurrent and undercurrent makes them an effective hazard control in workplaces where an equipment malfunction could cause injury.

Safeopedia Explains Current Relay

A current relay is an important part of electrical safety. Failure of an electrical system can endanger worker health and safety if it causes a machine or equipment to behave in an unsafe manner, or if the damaged system was operating as a hazard control. The processes necessary to repair a machine that has been damaged by an undercurrent or overcurrent may also expose workers to additional hazards.

Current relay provides an effective method of equipment protection because its action depends entirely on the strength of the current it is monitoring. A classical current relay utilizes an electromagnet, which is activated by the presence of a certain amount of current flowing through the system it monitors.

In instances where too much current flows through a piece of equipment, the electromagnetic field generated by the current will become sufficiently high to energize the overcurrent relay. This will cause the relay to switch on and perform whatever function it was designed to carry out to prevent damage to the equipment. On the contrary, low current flow (undercurrent) through a circuit will result in a small electromagnetic field. This reduces the strength of the current relay’s electromagnet, causing the circuit to switch off, and in turn deactivating the part of the equipment endangered by the undercurrent.

Because relays work by reacting to the electromagnetic field generated by the system they monitor, they don’t actually need to be integrated into the specific circuit they're monitoring. For example, overcurrent relays are often used as a type of protective relay, and they function by tripping a circuit breaker once they are activated by the presence of current flows that are too high. The quality standards that this type of protective relay must meet are prescribed by a number of different consensus standards, such as ANSI 50 & 51.


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