Every circuit requires a breaker. The breaker acts as a failsafe. It responds to excess current by tripping and disconnecting the power. While this is an inconvenience, it protects you and your equipment from fires and electrocution. But a breaker can only help you if you select the correct size. How do you choose the right breaker size?
What Size Breaker Do I need?
Air Conditioner/Heat Pump Breaker Size
| Safety Factor | Power | Voltage | Breaker Size |
| 75% | 2 ton (7033.71W) | 110 | 111.89 A |
| 75% | 2.5 ton (8792.13W) | 110 | 139.87 A |
| 75% | 3 ton (10550.6W) | 110 | 167.85 A |
| 75% | 4 ton (14067.4W) | 110 | 223.79 A |
| 75% | 5 ton (17584.3) | 110 | 279.75 A |
Breaker Size For Heater With 125% Rule
| Watt | Voltage | Breaker Size |
| 1000 | 110V | 11.36A |
| 1500 | 110V | 17.04A |
| 2000 | 110V | 22.72A |
| 3000 | 110V | 34.09A |
| 4000 | 110V | 45.45A |
| 4800 | 110V | 54.54A |
| 5000 | 110V | 56.81A |
| 6000 | 110V | 68.18A |
| 7500 | 110V | 85.22A |
| 10000 | 110V | 113.63A |
Well Pump/Motor Breaker Size
| Safety Factor | Power | Voltage | Breaker Size |
| 25% | 1/2 hp | 110 | 4.23 A |
| 25% | 2 hp | 110 | 16.94 A |
| 25% | 3 hp | 110 | 16.94 A |
| 25% | 5 hp | 110 | 42.36 A |
| 25% | 7.5 hp | 110 | 63.55 A |
| 25% | 15 hp | 110 | 127.10 A |
| 25% | 20 hp | 110 | 169.47 A |
| 25% | 40 hp | 110 | 338.98 A |
Breaker Size For Mini Split
| Safety Factor | Power | Voltage | Breaker Size |
| 75% | 12000 btu | 110 | 55.94 A |
| 75% | 18000 btu | 110 | 83.92 A |
| 75% | 24000 btu | 110 | 111.89 A |
Breaker Size For Shower
| Safety Factor | Power | Voltage | Breaker Size |
| 25% | 8.5 kW | 110 | 96.59 A |
| 25% | 9.5 kW | 110 | 107.95 A |
| 25% | 10.5 kW | 110 | 119.31 A |
Breaker Size For Generator With 125% Rule
| Watt | Volt | Breaker Size |
| 3500 W | 240V | 18.22 A |
| 5000 W | 240V | 26.04 A |
| 5500 W | 240V | 28.64 A |
| 7500 W | 240V | 39.0625 A |
| 8000 W | 240V | 41.66 A |
| 9000 W | 240V | 46.87 A |
| 9500 W | 240V | 49.47 A |
| 10000 W | 240V | 52.08 A |
| 12000 W | 240V | 62.5 A |
| 13000 W | 240V | 67.70 A |
Breaker Size For Inverter
| Watt | Volt | Breaker Size |
| 1500 | 12 V | 156.25 A |
| 2000 | 12 V | 208.33 A |
| 3000 | 12 V | 312.5 A |
Also, check the breaker size for different appliances,
How To Calculate The Correct Breaker Size With Respect To Watts?
The appropriate breaker size is not particularly challenging to calculate. It typically involves the following:
1). Identify The Wattage
You can start by calculating the current your devices will use. You can determine the current a device will use by checking its wattage.
According to wikiHow, you can find the wattage by simply looking at the data plate on the appliance.
It will give you all the information that matters, including the wattage and voltage. If you cannot find this information, record the serial number and send it to the manufacturer. They will respond with all the information connected to your device, including the wattage.
2). Get The Total Wattage
Once you identify the wattage of each device, calculate the total wattage. This means adding the wattage of all the devices together and recording the number.
3). Calculate The Amperage
The wattage cannot help you identify the correct size breaker. This is because manufacturers measure the sizes of breakers in amps. Fortunately, you can turn the wattage into amps. This is a simple matter of taking the total wattage and dividing it by the voltage.
For instance,
If your devices use a maximum of 150 watts, diving 150 watts by 120V will give you 1.25 amps.
You can either convert the watts of each device into amps before adding the amps together to get the total amps. Or you get the total wattage before converting the figure into amps. Either way, you will get the maximum number of amps you can expect all the equipment in your home to draw.
This goes without saying. You can’t just divide the total wattage by 120V. Use the voltage in your home. If you have 220V, use 220V in your calculations.
4). Get The Breaker Size
The purpose of calculating the total amperage is to ensure that you acquire a breaker whose size can meet the needs of all the devices in your home. You don’t want a breaker whose size is smaller than the total amps of your appliances. The appliances will draw more electricity than the breaker can permit.
This will lead to frequent tripping, which homeowners find annoying.
For instance, if your total amps are 22A, you cannot use a 20A breaker. The breaker is smaller than the load. If your total load is 22A, the breaker must be larger than 22A.
Don’t make the breaker size equal to the total load. The breaker size should be greater than the total load.
5). The 125 Percent Rule
You now know that the breaker should be larger than the total load. But how much larger?
The breaker should be 125% of a continuous load and 100% of a non-continuous load.
The 125% rule applies to continuous loads that use the maximum current for three or more hours. Non-continuous loads rely on short bursts.
Therefore, if you have a continuous load, take the total load and multiply it by 125 percent. This will give you the correct circuit breaker size. The 125 percent rule creates room for mistakes and errors.
For instance, if you use a 20A breaker to accommodate a 20A load, a spike in the current draw of appliances like freezers that use more power when they cycle on could easily overwhelm the circuit, causing the breaker to trip. But if you had a 25 to 30A breaker, it would accommodate the 20A load regardless of the unexpected spikes.
8). The 80 Percent Rule
Homeowners rarely take this precaution into account. According to the NEC, you should never use more than 80 percent of a circuit’s capacity. Therefore, if you have a 20A circuit, you can only use 16 amps. You can temporarily exceed this limit.
But if you have a continuous load, it could overload the circuit. Like the 125 percent, the 80 percent rule is a protective measure that leaves room for unexpected incidents to occur, such as surges caused by short circuits.
9). Checking the Breaker
If you already have a circuit breaker, you can check the size by reading the labels. You can do this if you’ve noticed signs of overloading, such as flickering lights. If the size of the breaker is clearly smaller than the size of the total load, you should replace the breaker.
This process is simple. Just pull the older breaker out of its slot and slide the new one into the space. Make sure you switch the power off before you proceed.
What Happens When I Use A Smaller Breaker Than Required?
In fact, many people use smaller breakers during emergencies. A smaller breaker is better than no breaker. However, smaller breakers are a nuisance. Because the devices react to excess current, a smaller breaker may trip the moment you switch the power on.
For instance, if your contractor installed a 30A breaker, more than likely, you have equipment in the house that uses anywhere between 25 and 30 amps. That 30A breaker can easily accommodate your electrical needs.
But if you install a 20A breaker, it will trip whenever you run your 25-30A equipment. Resetting the breaker won’t help you because it will trip again when you activate your appliances.
In that regard, a small breaker is not necessarily dangerous. However, it will keep the power in your house off. This is not a guarantee. At the end of the day, a 20A breaker will only react if you exceed its capacity. But what if you don’t exceed its capacity?
What if your total load is 16 amps or less? You can run your equipment without tripping the breaker. Before you replace a larger breaker with a smaller one, you have to stop and find out why your contractor installed the large breaker.
If they thought the larger breaker was necessary, make sure the new breaker matches the size of the old breaker.
What Happens If I Use Bigger Breaker Than Necessary?
A smaller breaker will trip continuously. Does that make a larger breaker the superior option? No. While a smaller breaker is a nuisance, a larger breaker is dangerous.
When you install a breaker of a particular size, you have to pair it with fitting wires. For instance, a 30A breaker will use 10-gauge wire. If you replace a 30A breaker with a 50A breaker, you are more likely to start a fire.
A larger breaker will cause the wires to overheat because they are too small to accommodate 50 amps of power. Usually, the breaker would prevent overheating by disconnecting the power the moment you force the wires to carry high volumes of current.
But because you have a 50A breaker, it will only trip once the current exceeds 50 amps. This is a problem because 10AWG wires will overheat long before the current gets to 50 amps.
Simply put, installing a larger breaker eliminates your safety net. It allows your system to transmit risky quantities of electricity. Again, these dangers are not guaranteed.
You don’t have to worry if you have no intention of using more than 30A even though you have a 50A breaker. But someone who doesn’t know better may connect a 50A appliance to the circuit because they think the wires can handle the load.
Does The Breaker Sizes Change With The Appliances Using The Same Watt?
If the appliances use the same watts, the breaker size will not change. For instance, a generator is seemingly heavier than a microwave oven. But if they both use 500 watts, a 20A breaker can accommodate them individually because it offers as many as 5,000 watts, depending on the voltage.
The number of appliances is more important. For instance, individually, you can run a 500W heater, oven, freezer, inverter, and generator on a 20A 110V circuit (2,200W).
However, you cannot run all those appliances simultaneously because their total wattage is 2,500, which exceeds the capacity of the 20A 110V circuit.
You are better off giving heavy-duty items like heaters dedicated 20A circuits. This will prevent overloading.
Wire Size VS Watt – Does The Wire Size Change With Watt?
The amperage affects the wire size. Each wire has an ampacity, which is the volume of current it can safely carry. If you exceed the wire’s ampacity, it will overheat, melt and start a fire.
For this reason, you have to match the wire gauge to the ampacity. For instance, you need 16AWG wire for a 10A load, 10AWG wire for 30 amps, and 8AWG for 40 amps.
The watts reveal the amount of electricity an appliance will draw. Therefore, they affect the wire size. You could start a fire if you connect a device with a high wattage to a smaller wire.
If you want to identify the appropriate wire size for a given wattage, start by changing the wattage to amps and then look at a chart.
| Wattage (110V) | Wire Size |
| 1000W | 16AWG |
| 1500W | 14AWG |
| 1800W | 12AWG |
| 2000W | 12AWG |
| 2500W | 10AWG |
| 3000W | 10AWG |
| 4000W | 8AWG |
| 4500W | 8AWG |
| 5000W | 6AWG |
| 5500W | 6AWG |
| 6000W | 6AWG |
| 7500W | 4AWG |
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