Do you need a GFCI receptacle for your home? If you do, what is the appropriate amperage to get? Does it make sense to add a 20-amp GFCI to a 15-amp circuit? What about a 15-amp GFCI on a 20-amp circuit? What would happen if you got that decision wrong?
How Do I Know If I Need A 15 Amp or 20 Amp GFCI?
For many people, their selection of a GFCI is determined by the types of devices and appliances they want to operate. They are convinced that the amperage of the GFCI has to match the total amperage of the devices that GFCI will operate.
For people with this mindset, a method that can determine whether the total draw of all your appliances matches the amp rating of the GFCI:
1). Find The Wattage
You have to start by calculating the amount of electricity your appliances will use if you connect them all to the same GFCI. This creates a problem. Many appliances are rated in watts.
You cannot compare the wattage rating of your appliances to the amp rating of a GFCI. Fortunately, this problem has a solution.
Start by adding up the wattage of all your appliances. Record the total on a piece of paper so you don’t forget it.
2). Take The Amperage Rating
Now that you know the total wattage of your appliances, you can turn your attention to the GFCI. Take the amperage rating of the GFCI and multiply it by the voltage of your power supply.
For instance, American households use 120V power supplies.
If you have a 15A GFCI, multiply 15 by 120V. This will give you 1800W.
1800W is the total number of watts the breaker can tolerate. But it isn’t the total number of watts you can use.
The NEC expects consumers to use only 80 percent of the maximum allowable wattage. In this case, 80 percent of 1800W is 1,440W.
3). Compare The Total Wattage With The GFCI
1,440W is your target.
The total wattage of all the appliances that the GFCI will support cannot exceed 1,440. If the total wattage of the appliances is greater than 1,440W, you need a new GFCI breaker with a superior amperage.
This method prevents you from installing a GFCI of the wrong amperage.
But what if you don’t want to do these calculations? What if you cannot figure out the total wattage of all your home’s appliances and devices?
Well, you have a simpler solution. At the end of the day, GFCI receptacles are expected to act as a replacement for your ordinary outlets. This means that the capacity of a GFCI receptacle has to match the capacity of the ordinary outlet it will replace.
The rules governing the selection and installation of ordinary outlets are surprisingly straightforward:
The Selection And Installation Of Ordinary Outlets
1). Circuit Rating
Most homes in the United States use 15 and 20A circuits. The chances of finding a 30 or 40A circuit in a residential setting are very low. Habitable homes do not require that much power.
Any calculations you have to do with regards to selecting a GFCI of the right amp rating will revolve around a 15 or 20A circuit.
2). GFCI Rating
The amp rating of an outlet has to match the amp rating of a circuit. In other words, if you have a 15A circuit, you should install 15A outlets. If you have a 20A circuit, you should install 20A outlets.
Can you install a 15A outlet on a 20A circuit?
Yes, you can. The rating of an outlet can be equal to or less than the rating of a circuit. But the rating of an outlet cannot exceed the rating of the circuit to which it is attached. Therefore, 15 or 20A outlets are compatible with a 20A circuit.
You cannot add a 20A outlet to a 15A circuit. The practice is dangerous because it allows the outlet to transmit more electricity than the circuit can handle. In the best-case scenario, a 20A outlet will cause the 15A circuit breaker to trip. In the worst-case scenario, the breaker will fail to respond and a fire will start.
These same considerations apply to GFCI receptacles, which is why I expect consumers to install 15 or 20A GFCIs on a 20A circuit and 15A GFCIs on a 15A circuit.
Do not attach 20A GFCIs to 15A circuits.
3). Finding The Rating
If you installed the original outlets, the GFCIs won’t present a challenge because you can just apply the same logic you used when you installed those original outlets.
If you did not install the original outlets but you want to add the GFCIs yourself, try to match the rating of the GFCI to the rating of the outlet.
For instance, if you want to replace a 20A outlet with a GFCI, make sure you use a 20A GFCI as well. If the outlet has a 15A rating, use a 15A GFCI.
If you don’t know the rating of your outlets, you can find out in two ways:
- Outlet – Check the outlet. Some outlets have labels that clearly reveal the rating.
- Breaker – Go to the electrical panel and find the breaker that feeds the outlet. The breaker is also marked. To find the breaker that feeds the outlet, plug a light into the outlet and switch it on. Start flipping the breakers off one at a time. The right breaker will cause the light to go off. Mark it with tape and take note of the amp rating. That is the rating your GFCI should have.
What is the Difference Between 15 Amp and 20-Amp GFCIs?
15 amp and 20-amp GFCIs are not the same. They have various differences that affect the work they do, for instance:
1). 20A Have T-Shaped Neutral
You won’t have any trouble differentiating between 15 and 20A GFCIs because they don’t have the same design. Just like ordinary outlets, 15 and 20A GFCIs have three slots.
They are designed to accommodate 3-prong plugs. 20A outlet has a T-shaped prong. This is neutral.
A 15A receptacle does not have a T-shaped neutral.
20A plugs can only enter 20A outlets. This applies to 15A outlets as well.
Many people look at the labels that accompany their appliances to determine whether or not they require a 15A or 20A circuit.
But in many cases, if you look at the plug of the appliance, it will show you the type of outlet it requires. This, in turn, will help you identify the right circuit for the appliance.
2). 20A Is Used For Heavy Duty Appliance
20-amp outlets can transmit more power than 15-amp outlets. Therefore, 20-amp outlets must be installed in places like the kitchen, bathroom, and laundry room that normally house heavy-duty items like washing machines, hairdryers, and microwave ovens.
You don’t have a choice in the matter. The regulations governing electrical installations in most places expect homeowners to use 20A outlets in the kitchen because they contain appliances that consume a lot of power.
Therefore, you need 20A GFCIs in the kitchen, bathroom, laundry room, garage, and any other location with heavy-duty appliances.
You can use 15A outlets in every other location. They are commonly used for lighting purposes. Places that require 15A outlets should be used to accommodate 15A GFCIs.
You shouldn’t install a 15A GFCI in the kitchen when kitchens clearly require 20A receptacles. On the other hand, you are free to add 20A receptacles to places that require 15A outlets. There is no downside to this practice.
3). 20A Is Costlier
Many homes use 15A outlets because they are cheaper than their 20A counterparts. This is true for GFCIs as well. However, the difference in cost is small. In the long run, it shouldn’t impact your decision to use either 15 or 20A GFCIs.
4). You Can Plug 15A And 20A GFCI To 20A Circuit
You can connect both 15A and 20A GFCIs to 20A circuits. But you can only connect a 20A GFCI to a 20A circuit. A 20A GFCI on a 15A circuit is inappropriate and dangerous.
5). You Can Use 14 Gauge Wire For 15A While 12 Gauge For 20A
With 15A circuits, you need a 14-gauge wire. 20A circuits, on the other hand, should be paired with 12-gauge wire. You can use a 10-gauge wire or even higher if the wires have to cover a large distance.
The difference in the gauge makes sense. A 20A GFCI is designed to transmit more power than a 15A GFCI. Therefore, it requires larger and thicker wires.
Can I Use 15 Amp GFCI On 20 Amp Circuit?
The NEC prohibits people from installing outlets that exceed the rating of their circuits. A 15A GFCI can run on a 20A circuit because it has lower power requirements than the circuit’s rating. It is less likely to overwhelm the circuit.
Can I Use 20-Amp GFCI On 15 Amp Circuit?
You can’t use 20A GFCI on a 15A circuit because a 20A GFCI will draw more power than the 15A circuit can handle. This will cause the breaker to trip. If the breaker malfunctions, you could start a fire, especially if you are using that 20A GFCI to operate a 20A appliance.
15A GFCI Pros & Cons
- They are slightly cheaper than 20A GFCIs
- Most devices in a home can run on 15A GFCIs
- Easy to find
- They rely on 15A circuits which use cheaper 14-gauge wire (in comparison to the 12-gauge wire that 20A circuits use)
- You can add them to 20A circuits
- They cannot run heavy-duty appliances
- The NEC prohibits you from installing them in locations like the kitchen and bathroom
20A GFCI Pros & Cons
- They can run heavy-duty appliances
- They can transmit more power
- You can connect more devices and appliances to a 20A GFCI
- They are more expensive than 15A GFCIs
- Their circuits require 12-gauge wire or higher which is more expensive than the 14-gauge wire that 15A circuits use
- They require a specific type of plug with a prong that can fit in the T-shaped neutral of a 20A outlet
- You can’t add them to 15A circuits
What Amp GFCI Should Be Used in Bathroom, Kitchen, Garage?
You have to add GFCIs to any space that exposes the outlets in the vicinity to moisture. That includes the bathroom, kitchen, and even garages.
Though, the NEC only expects to see GFCIs in grade level or below grade level garages that are not meant to act as habitable rooms. You also need AFCI protection on 15 and 20A circuits.
But what is the appropriate rating for a GFCI in these locations? You need 20A receptacles.
They transmit more power, which means that they can operate heavy-duty appliances like microwaves and freezers.
You don’t have freezers and microwaves in the garage. But you probably have workstations with drills, compressors, and other power tools. Naturally, these require 20A circuits, outlets, and GFCIs.
Bathrooms are in a similar boat. If you want to run your hairdryer safely, you need a 20A circuit and outlet.
You could experiment with 15A GFCIs in these locations if you do not have a choice. However, doing so would contravene the regulations of the NEC. Unless your local code says otherwise, the NEC wants 20A outlets to support the kitchen countertop.
Of course, you can ignore the NEC if your local code has loopholes that permit homeowners to use 15A outlets. But even if that was the case, the appliances that require a 20A circuit would overwhelm 15A outlets, causing the breaker to trip.
Don’t forget: the GFCI will not respond to overloading. It is designed to defend homeowners against electrocution in the event of a ground fault. It cannot stop fires caused by overloading.
You have to rely on the breaker to play that function. But if the breaker refuses to respond because of a defect or malfunction, an overloaded 15A circuit in a kitchen, bathroom, or garage could start a deadly electrical fire.