Ground Fault Circuit Interrupter Fundamentals & Primer

In this guide you will learn about ground fault circuit interrupters (GFCIs) and how their effective use can help to protect your personnel and equipment.


Ground Fault Circuit Interrupters are complex devices that save lives and protect equipment every day in tough work environments. Whether it is due to water or damaged equipment and cords, ground faults can occur quickly and, if not resolved immediately, can result in severe injury or electrocution. 

We understand GFCIs and how they work in your tough environments.  The information provided here will help you to determine what you need.  Our technical sales group is always available if you require more in-depth assistance


Several different acronyms are used to describe the very similar function of interrupting ground faults.  The difference between them comes down to standards that have been established in different jurisdictions, and for different purposes. 

A GFCI, by standards definition, must trip the circuit if a ground fault occurs with a maximum of 6mA of current loss to ground.  GFCIs are typically considered personnel protection devices and the maximum 6mA trip level is set at a level to protect injury to people.

An ELCI (Equipment Leakage Circuit Interrupters) has trip levels at or greater than 6mA, and is considered an equipment protection device.  While it performs the same function as a GFCI, the trip level is often set higher to reflect that higher voltage and amperage devices typically will leak current in the normal course of operation.  Setting the trip level higher ensures that the equipment is protected from abnormal current loss while minimizing 'nuisance tripping' due to normal current loss.  ELCIs are also sometimes called EGFPD (Equipment Ground Fault Protective Devices), which is a standard set by UL to encompass the ELCI set of products

Trip Levels

The trip level refers to the amount of current loss to ground that will cause the GFCI or ELCI to 'trip', or cut off the power sent down the line.  Lind's GFCIs have trip levels of 4-6mA, while our ELCI/EGFPD devices range from 6-50mA.  Trip levels of 4-6mA are considered "Class A" in Canada.  Generally, the lower the trip level, the more safety that is delivered by the device.  However, in equipment protection, this needs to be weighed against the amount of natural current loss that occurs with heavy current loads.  This is why the ELCI/EGFPD lines were created

Trip time

Trip time is the amount of time it takes for the device to cut off the power to the line after sensing the appropriate amount of current loss to ground.  All of our GFCI/ELCI/EGFPD products are designed to trip in less than the UL/CSA/ANCE standard of 25mS.  The shorter the trip time, the less chance of personal or equipment injury.

Manual vs. auto reset

If there is a power outage on a circuit that a GFCI is attached to, the reset type controls whether the GFCI will allow power to go down the line once the source power is turned back on.  Manual resets are typically requested for industrial workplaces, where a sudden resumption in power could be dangerous as tools and equipment may start back up unexpectedly.  A manual reset requires the user to reset the GFCI after a power outage.  Automatic resets will allow power back down the line as soon as the power supply is restarted.

GFCI placement in a circuit

Generally, we recommend that a GFCI is placed as close to the source of power as possible in a circuit.  For example, suppose you are operating a tool with a 100' of cord and want to add a GFCI to the cord for protection.  We would recommend placing the GFCI as close as possible to the plug at the start of the cord - either with a GFCI plug and cord set or an in-line GFCI placed at the plug end.  Putting the GFCI close to the source of power ensures protection along the entire cord length.