What is a Ground Fault Circuit Interrupter?

A GFCI is not be used to replace a fuse and does not protect against circuit overloads, short circuits, or shocks. Its working voltage is 264VAC-102VAC, working temperature is 35Deg~66Deg. America has very strict GFCI certifications which mainly include UL and ETL certification, if you do UL certification, all tests of products are carried out in UL laboratory in the United States; if ETL certification is done, tests can be carried out in China.

Catalog:

I Classification

According to different wiring methods, GFCI can be divided into:

1.Receptacle-type ground-fault circuit-interrupter

The protector uses a socket to output and connects with the plug of the load equipment.

2.Portable ground-fault circuit-interrupter Portable ground-fault circuit-interrupter

The protector uses a plug to connect to the socket of the power supply circuit, and the position of the protector relative to the power supply circuit is not fixed. The parts of the protector (including the protector shell and the output socket) can be easily moved. According to the distance between the protector shell and the plug, it can be divided into:

a.Plug-in ground-fault circuit-interrupter 

The protector shell is glued to the plug as a whole, and the shell and the output socket are connected by cables or wires.

Figure 1:  Plug-in ground-fault circuit-interrupter 

b. In-line type ground-fault circuit-interrupter

Cables and wires with plugs are drawn from the protector shell, and the plugs are connected with the sockets of the power supply circuit. The protector shell and the output socket shell can be made into a whole or can be connected by cables or wires.

Figure 2: In-line type ground-fault circuit-interrupter

II Characteristic

Because GFCI detects ground faults, it can also prevent some electrical fires. In a household wiring system, on a power outlet, under normal circumstances, the current of the hot wire and the neutral wire should be equal. GFCI monitors the current difference. If the difference is greater than 6 mA (according to the UL943 standard, when the leakage current is 6mA, the disconnection time is 25 milliseconds), it can cut off the power at 0.025s (disconnection time when the leakage current is 4-6mA in the case of 500-ohm impedance according to the UL943 standard) to ensure personal safety. The GFCI interrupts power faster than a blink of an eye to preventing lethal power. You may receive a painful shock, but you will not be electrocuted or receive severe shock injuries.

All GFCIs should be tested every time when they are used to ensure that they can work properly and to protect you from fatal shocks. GFCI should be inspected after installation to ensure they can work and properly protect the circuit. To test the GFCI socket, first, plug the nightlight or lamp into the power socket, then the light should be on at that time. When pressing the "TEST" button, the "RESET" button of the GFCI should pop up and the light will go out. If you press the "reset" button, it pops up, but the nightlight is not off. In this situation, the GFCI has been improperly wired. Contact an electrician to correct the wiring error. If you press the "reset" button, it does not pop up, which shows that the GFCI is defective and should be replaced.

III Working Principle

GFCI uses the circuit to detect the opening or closing of the circuit, and the Reset Button (or indicator light) displays the current state of the circuit so that the user can know whether the circuit is currently in a normal working state or a faulty state. In order to improve the safety of use, an auxiliary switch is set to control the power supply of the circuit board to prevent the circuit board from being damaged due to current overload. It is designed to have the function of automatically disconnecting the circuit to avoid electric shock caused by foreign matter in the load, that is when the live wire of the working circuit is grounded through the foreign matter. This kind of function is for some customers who are at risk of electric shock, when a strong current flows through their bodies, the power supply will be automatically removed.

GFCI checks the balance of the current flowing through the live wire and the neutral wire. If the neutral wire current suddenly becomes much smaller than the live wire current, an electric shock may have occurred. A part of the current flows back to the ground wire through a loop outside the neutral wire. If the current of this part is between 4.2mA and 5.8mA, or greater, GFCI will send out a pulse that cuts the power of the load circuit through a mechanical structure. GFCI limits the time that the electric shock current flows through the body of the shocked person instead of the size of the current. This time is calculated based on physiological data to avoid damage to the health of ordinary people. GFCI has a simple appearance and inherits the original functions of GFCI products. The operation of Bridge Contacts strengthens the ability to solve faults caused by the reverse connection of the power input line and the load output line, and prevents the loss caused by the initial wiring errors of the installer, thus further improving the function of the leakage protector. 

What to do if the GFCI trips:

In some cases, GFCI’s will trip but this does not mean that there is something wrong with the installation. One of the reasons that the GFCI is tripping is that it is installed in circuits longer than 100 feet. When there are many splices, fluorescent lighting fixtures, or permanently installed electric motors in the circuit, there will be another problem because this can cause the GFCI to trip. If the GFCI is installed in circuits longer than 100 feet, this could be one of the reasons your interrupter is tripping. Another issue can occur when the circuit has many splices, fluorescent lighting fixtures, or permanently installed electric motors as this can cause the GFCI to trip. When using the protection with freezers, garage door controls before installing a GFCI, the power may be cut. Be aware that during the installation, the lines and/or loads should be properly landed to ensure that the device will work properly, if not, the GFCI will not reset, so you should make sure the connections are right.  The GFCI is not the same as the ACFI. The AFCI is used to address fire hazards, while GFCI is installed to prevent shock hazards. 

IV Application

GFCI can be widely used in high-pressure electric washing machines, electric lawnmowers, electric water pumps, large electric bathtubs, electric harvesters, electric water mills, electric cutting machines, hand-held power tools, etc.

V  Main brands

In the US market, plug-type GFCI is commonly seen, and its brands have LEVITON, TOWER, ELEGRP, DEFOND, NANDAO, etc. In the domestic market, leakage protection heads and leakage protection sockets are commonly seen. Suzhou Lumeisi Electric Co., Ltd. has 15 years of production experience in GFCI. It independently researches and develops, and produces GFCI, GAB, Jiaanbao, and leakage protection walls. Its products include five series: leakage protection series, leakage overcurrent protection, intelligent protection, current limiting protection, and Camry.

American Leviton (LEVITON), founded in 1906, headquartered in New York, is a global leader in the manufacture of electrical accessories, lighting control, energy management, and structured wiring products. Leviton has 35 factories worldwide, mainly in the United States, Canada, Mexico, and China. All factories have passed ISO9001/2001 certification and have highly automated production lines; provide a complete set of high-quality products and services, including design, modeling, production, and logistics. 

American TOWER is affiliated with the American TMC (Tower Manufacturing Corporation). TMC, founded in 1957 and headquartered in Rhode Island, is a professional manufacturer of switch products. The products involve GFCI, ALCI, LCDI, and other professional leakage protection products. All are applicable in different industries and products and have obtained UL certification. It has wholly-owned subsidiary factories in the United States and Shenzhen, China, as well as a branch in Hong Kong. The company has a complete R&D, design, production, sales, and after-sales service team.

ELEGRP is the only private company to obtain UL certification in the field of portable leakage protectors. It was established in Shanghai in 2000 and has four branches. At the end of 2010, it relocated to Suzhou Industrial Park. Its main markets distribute in the United States and Canada. It has more than ten years of experience in the North American leakage protector market. The products involve professional leakage protector products such as GFCI, LCDI, PRCD, etc. Relying on its own strong R&D capabilities, it has solved technical difficulties and avoided the United States patents, independently designed and developed products, and obtained several Chinese patents and US patents. The company also produces other series products of wiring devices, such as switches, plugs, sockets, etc., all of which have obtained UL and CUL certification.

DEFOND and NANDAO are mainly Hong Kong and domestic companies. Among them, DEFOND has also begun to involve other industries, including automotive electronic parts.

Reference

1. Guardian GFCI (n.d.). GFCI Defined. https://www.guardiangfci.com/knowledge/gfci-defined

2. Electrical Technology (2024). GFCI (Ground Fault Circuit Interrupter) - How Does it Work?  https://www.electricaltechnology.org/2015/02/gfci-ground-fault-circuit-interrupter-types-working.html

3. Harvard Environmental Health & Safety (2014). Ground Fault Circuit Interrupter (GFCI) Fact Sheet.  https://www.ehs.harvard.edu/sites/default/files/ground_fault_circuit_interrupter_gfci_fact_sheet.pdf

4. Electrical Safety Foundation International (n.d.). GFCIs. https://www.esfi.org/resource/gfci-safety-101-0 0