In order to confirm what size GFCI breaker is needed for a 20 amp breaker, you will need to know (1) the wire gauge of the branch circuit on which you want to install the GFCI outlet and (2) what is the rating of the associated circuit breaker. Generally, a 20 amp circuit should be properly served by a 20 amp GFCI circuit breaker, but a review of the wires’ gauge and the rating of the associated circuit breaker in the breaker box will confirm this.
Understanding wire gauge
Wire gauge refers to the thickness of the wire. This is important because the thicker the wire, the more current can travel through it. In the same vein, a thinner wire will inhibit the amount of current that should pass through it. The lower the number of a wire’s gauge, the thicker the wire. So a 12 gauge wire is thicker than a 14 gauge wire. When evaluating a wire’s gauge, often the acronym “AWG” is used. AWG stands for American Wire Gauge and is a standardized measurement that is commonly used in North America.
Wire gauge and GFCI breakers
A 20 amp circuit should be wired with wire that has a gauge no greater than 12 AWG. A 15 amp circuit should be wired with wire that has a gauge no greater than 14 AWG. If you are trying to install a GFCI circuit breaker on the 20 amp circuit, then a GFCI breaker 20 amp rated should be no problem if modern electrical guidelines (Read: electrical code) have been properly followed. If you live in an old house or are unsure of the wiring work that has been performed on a circuit, then you should confirm the wire’s gauge. Typically, this can be found on the sheathing of a wire, but if it cannot be confirmed through a simple visual inspection, then an electrician should be consulted to perform a professional review.
You can install a 15 amp GFCI breaker on a 20 amp circuit, although this is not advisable as it will restrict the amount of amperes that can be run through the circuit. If the circuit has been set up for 20 amps, through proper wiring, then it is best to use a GFCI breaker that matches so you can get full usage out of that circuit. Take, for example, a typical kitchen, which is often on a 20 amp circuit: If you were to put a 15 amp circuit breaker on the circuit, then you are limiting the current to 15 amps on that circuit. Most modern refrigerators are recommended to be on a dedicated 15 to 20 amp circuit, though it is common that refrigerators not be on a dedicated circuit. If you have a refrigerator on a non-dedicated 15 amp circuit, it would be easy for another household appliance, such as a hot water kettle, to trip that circuit if it is running at the same time as when the refrigerator’s compressor comes on.
Mitigate risks of Overcurrent
Unlike using a 15 amp GFCI breaker on a circuit designed for 20 amps of current, you should absolutely not use a 20 amp GFCI breaker on a circuit designed for 15 amps of current. This type of installation would cause a safety hazard, as opposed to a possible inconvenience. If a GFCI breaker for 20 amp current is placed on a 15 amp circuit, then it will allow up to 5 amps more current than the circuit is designed to support. The GFCI would effectively be useless as the wiring could fail from this additional current before the GFCI breaker trips. In this case, the wiring would likely get overheated and pose a serious fire risk.
The preceding cautionary example would present what is known by the National Electric Code (NEC) as overcurrent. Overcurrent, sometimes also called excessive current, is simply “any current in excess of the rated current of the equipment or the ampacity of a conductor.” Overcurrent can be caused by overloading a circuit, like in the above, or it can be caused by defective equipment, wiring, or insulation. Any electrical work must be conscious of the risks posed by overcurrent and how to avoid it. Using an appropriately rated GFCI breaker will help mitigate the risks of overcurrent from defective equipment while a GFCI breaker designed for larger circuits with more current can do the opposite.
How to change a circuit breaker
If you are looking to install or replace a circuit breaker, the most common place to do this is at the breaker box. Sometimes, there will be multiple breaker boxes in a structure and even smaller homes may have a sub panel on the outside of the house to control exterior equipment like HVAC condensers, pool pumps, or exterior outlets.
There are two fundamental questions that any DIY-er needs to ask themselves before installing a new circuit breaker: (1) How comfortable are you in working around electrical currents that can kill a person? (2) Is the electrical power to your home shut off? If there is hesitation in answering either of those questions, then you should avoid working around a breaker box and contact a licensed, experienced electrician. Changing out an electrical circuit breaker is a relatively straightforward task that a qualified professional should be able to handle quickly and without too much expense to the homeowner.