What is a Ground Fault?
Before looking at Ground Fault Interrupter (GFI) and Ground Fault Circuit Interrupter (GFCI), you have to first understand the meaning of Ground Fault. Here is a simple explanation of Ground Fault for beginners and novices. We will understand the meaning of Ground Fault by taking an everyday electrical appliance i.e., a lamp. Whenever we plug the power cord or a lamp into an outlet, the following sequence of things happens. Electric current from the Hot slot of the outlet enters the hot terminal of the lamp’s power cord and then into the lamp. The lamp will glow and returns the current through its neutral wire. From the neutral wire, the current returns to the neutral slot of the outlet after passing through the neutral terminal of the power cord. This is the normal flow of current for the lamp (for that matter, any electrical appliance). The lamp continues to glow as long as this path of electric current is complete. Now imagine there is a small cut in the Hot Wire and you accidentally touched the exact spot on the wire. Electric Current always tries to take the least resistance path. Keeping this in mind, the moment you touch the exposed hot wire, electric current start to flow through your body and to the ground as this path offers the least resistance of all. This is Ground Fault. The result is a severe electric shock to you. The circuit breaker doesn’t trip in this case because there is no overload on the circuit. This is because the circuit breaker doesn’t care if the current is returning through neutral or not. All it cares about is if the circuit draws a current in excess of its rated value.
What Causes Ground Faults? How Dangerous is it?
As we mentioned earlier, any cuts on the wires due to accidental handling, rodents chewing them off, or any other reason will expose the conductors. Old or worn-out wires can also have their insulation come off over time. Water is also one of the main reasons for ground faults. Places such as bathrooms, kitchens, washer or dryer locations, etc. have the risk of causing ground faults. If there is a fault in the wiring or if there is a problem with the electrical appliance itself, then also there is a chance of ground fault. Irrespective of the reason for ground faults, they are very dangerous and can cause severe electric shock. A study says that the human body can handle electric currents up to 6mA without any harm. You will feel the shock but there won’t be huge damage. If the current due to ground fault is more than this value, the electric shock will cause burns or in the worst case, it could be fatal. Apart from electric shocks, ground faults can also start fires.
What are GFI and GFCI?
Now that we have seen a little bit of ground fault, let us turn our attention to GFI and GFCI. GFI is short for Ground Fault Interrupter and GFCI is short for Ground Fault Circuit Interrupter. GFI is a special type of receptacle that protects us from ground faults. You might have seen GFI receptacles in bathrooms and kitchens with “TEST” and “RESET” buttons in the middle. GFCI also does the same thing but it protects the entire circuit from ground faults rather than a single outlet in the case of GFI. It is essentially a type of circuit breaker that has additional ground fault protection. So, GFI is essentially a receptacle with two outlets and GFCI is a type of circuit breaker. But we often use the same name i.e., GFCI for both receptacles as well as circuit breakers. If you hear GFI Receptacle or GFCI Receptacle, they both are the same. But GFCI Breaker is different in the sense that it is a circuit breaker that we have to install at the distribution panel or service panel. GFI protects only the two receptacles from ground faults. But the advantage of GFCI Breaker is that apart from acting as an overcurrent protection device (trips if the current draw in the circuit is more than its rated value), it also protects all the devices in the circuit from ground faults.
How Does GFI or GFCI Work?
From the above discussion, it is clear that both GFI and GFCI are ground fault protection devices. One is a local protection device (GFI) while the other is a circuit-wide protection device (GFCI). Their working is also the same. They essentially measure the current leaving the hot wire and the current returning the neutral wire. If there is an imbalance as little as 5mA, the GFI or GFCI detects this as a ground fault and opens the circuit (or outlet). There is a complex circuitry in GFI and GFCI devices that help in measuring and comparing the currents in both hot and neutral wires. But here is a very simple explanation. Both hot and neutral wires pass through a toroidal ring. These two wires act as one side of the transformer (you can assume it is primary) while a special pick-up coil acts as the other side of the transformer (you can call it secondary). The toroidal ring acts as the core of the transformer. Under normal operating conditions, the current through these wires is equal and opposite. So, the voltage generated by the hot and neutral wires cancels out each other. As a result, there will be no voltage induced in the secondary coil (the pick-up coil). Now imagine there is a ground fault i.e., the current leaving the hot is not the same as the current returning through the neutral wire. Some amount of current is finding an alternative path to ground (through humans or any other means). This difference in currents will generate a net voltage on the primary side and as a result, a voltage is induced on the secondary side. A sensor will boost the voltage on the pick-up coil and activates a solenoid to open the circuit. The reaction time of both GFI and GFCI is excellent. As soon as it detects a ground fault, it opens the circuit (or outlet) in less than 25ms. Both GFI and GFCI work similarly but the main difference is the stretch of their protection. With the help of a GFI (commonly known as GFCI Receptacle) can provide ground fault for two of its outlets and with proper wiring one or two other receptacles as well. The GFCI (GFCI Circuit Breaker) provides protection against overloads as well as ground faults for the entire circuit.
Differences: GFI vs GFCI
From the above discussion, it is clear that both GFI and GFCI are ground fault protection devices. But are there any differences between them? Let us make a simple GFI vs GFCI comparison to figure out their subtle differences. Before proceeding, you need to understand that GFI is often called GFCI while GFCI Circuit Breakers are simply known as GFCI Breakers. Apart from these two, we also have another type of GFCI device known as Portable GFCI. This looks like an extension cord but by using this, you can convert a regular outlet into a GFCI outlet for working outdoors.
1. Protection
Both GFI and GFCI are essentially ground fault protection devices. They trip the outlet or breaker as soon as they detect any ground fault. As the GFI is a Receptacle, it can protect its two outlets from ground faults. With some wiring tactics, you can add ground fault protection to another outlet as well. Coming to the GFCI Breaker is basically a circuit breaker that can protect against ground faults. So, it has all the protection aspects of a typical circuit breaker i.e., overcurrent protection and short circuit protection. In addition to these, the GFCI Breakers also protect the entire circuit from ground faults. So, all the outlets in that circuit (be they normal outlets or GFCI outlets) have ground fault protection.
2. Installation
You might have guessed where to install GFI and GFCI from the previous point. GFI is a receptacle. So, you can install them everywhere you need outlets. NEC requires GFCI Outlets in a certain location where the chance of electric shock is more. Some common locations are the bathroom, kitchen, laundry area, basement, crawl space, fountain, etc. GFCI Breakers are a type of circuit breaker. So, we have to install them in service panels. We recommend installing GFCI Breakers so that they add protection to all the devices, appliances, and outlets in the circuit.
3. Testing
Both GFI and GFCI devices have manual testing features. In the case of GFI Receptacles, you can see two buttons between the two outlets with the names TEST and RESET. When you press the TEST button, it creates a ground fault error in the GFI. If there is no problem with the devices, it should immediately trip and turn off the power through the outlet. Press the RESET button to bring the GFO to normal operation. Most GFCI Receptacles nowadays have an LED to indicate the status. One common configuration of LED is as follows; if the LED is green, the GFI is operating normally. When we press the test button or the if it trips after detecting a ground fault, the LED turns off. If the red LED is on or blinking, you have to give your attention to the GFI. A simple TEST and RESET might fix this problem. If not, you have to replace the device. GFCI Breakers also have similar testing features. Usually, there will be a TEST button on the GFCI Breaker. When you press this, it will create a ground fault and trips the breaker. You can reset the GFCI breaker just as you reset a regular circuit breaker (by toggling the lever). Be very careful when testing GFCI Circuit Breakers as you have to access the main service panel to do this. Many experts recommend testing GFI or GFCI once every month. If you find a fault while such tests, you can immediately replace the device.
4. Cost
GFI Receptacles are available as 120V 15A and 12V 20A Outlets. You can get them in other configurations as well but these two are more common and popular. If you take the 120V 15A GFCI Receptacle, it will cost around $15 to $20. Similar to GFI Receptacles, you can get the GFCI Circuit Breakers in 120V 15A and 120V 20A variants. The cost of a 120V 15A GFCI Circuit Breaker is around $50 to $55.
Conclusion
Ground Fault Circuit Interrupters or GFCI is a very useful devices. It detects ground faults and opens the circuit, thus preventing severe electric shocks or burns. If you are shopping for GFCI devices, you can find them as receptacles or as circuit breakers. Technically, the receptacle-style devices are known as Ground Fault Interrupters or GFI and the circuit breakers are known as Ground Fault Circuit Interrupters or GFCI. These names are lost in translation and most electricians or vendors use the term GFCI for both receptacles as well as circuit breakers. In this guide, we saw the meaning of GFI and GFCI and understood the similarities and differences between these two by comparing GFI vs GFCI. We hope that this guide could help you in learning the basics of GFI and GFCI devices. If you feel we missed something or want us to add anything, do let us know in the comments section. It will not only help us but other readers as well. Comment * Name * Email * Website
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