Are you worried about busting your water heater or setting your house on fire for not using the correct circuit breaker? I know the feeling. I asked myself what size breaker do I need for a water heater, too.
Choosing the wrong breaker can have serious consequences. That is why I will help you determine the correct size of a circuit breaker to use for your water heater.
Table of Contents
How Does a Conventional Water Heater Work?
Before I guide you in determining the correct size of a circuit breaker to use in your water heater, let us get down to the basics first.
A typical electric water heater has two thermostats and two heating elements located in the upper and lower sections inside a tank. Once the tank is full of water, the upper thermostat activates its heating element to raise the water temperature in the upper section.
Heat moves towards the bottom, activating the lower thermostat and kick-starting its heating element. Around this time, the upper thermostat switches off because it has already achieved its purpose.
On the other hand, the lower thermostat continues controlling, the lower heating element until it achieves the water heater’s desired temperature. It then switches off.
The lower thermostat turns on and activates the lower heating element for about 1 to 4 minutes every hour, around the clock. It does this to maintain the water’s ideal temperature.
How Does Electricity Heat the Water?
Based on our discussion above, your water heater needs electricity to operate the heating elements. Your residential electrical system’s voltage pushes electrons as amperes through a conducting wire. All wires offer resistance, reducing electrical flow. It also creates heat.
When the electrons reach the water heater’s heating element, the voltage pushes these electrons through a resistance wire within the heating element. Engineers designed these resistance wires to reach extremely high temperatures without melting.
As the resistance wire heats, it also heats the water in your tank.
What is a Circuit Breaker and Why Do You Need It?
Remember what we said about the voltage pushing the electrons through the wire, producing heat? If there is excessive heat on the wires, it can melt the wire covering and start a fire. There must be a mechanism that will stop the flow of electricity from the source to the water heater.
A circuit breaker ‘trips’ to break the electrical flow from the source to the heating elements when there is too much electricity passing through the circuit. In other words, it disconnects the water heater from the power source, saving the appliance’s integrity and your home.
What is the Correct Circuit Breaker Size?
Manufacturers rate circuit breakers according to the maximum electric current (in amperes) they can accommodate without tripping or breaking the circuit.
The National Electrical Code (NEC) requires electricians to observe the 80% rule when sizing an overcurrent protective device, such as a circuit breaker. The code states that a circuit breaker should not handle more than 80% of its electrical rating.
The 80% rule offsets the amount of heat generated in the electrical circuit on a continuous load of at least three hours.
An appliance running continuously 24/7 should have a circuit breaker with 125% of its power rating. If the device does not require a continuous electrical load, a circuit breaker with 100% of its rated capacity can accommodate said device.
Given that water heaters operate continuously, it would be safe to size your circuit breaker at its 125% rating.
What Size of Wiring Do I Need for My Water Heater?
In general, the smaller the diameter of the electric wire, the faster it tends to heat. That is why it is best to get a wire with a large gauge.
The NEC recommends using a Gauge 10 non-metallic or metal-clad electric cable with two conductors (10/2) for 4500-watt water heaters. If your water heater has 3800-watt heating elements, you can use a 12/2 wire (Gauge-12 and two conductors).
It is also important to remember that your water heater requires a dedicated voltage and breaker system. Most of the appliances we have at home run on 110-120 volts. Water heaters require 240 volts to push the electrons through the cables.
Because your water heater runs on 240 volts, it also requires a double-pole circuit breaker. This CB type has two live wires. If a problem occurs in one of the wires, it also trips the other to cut off electricity to the water heater.
You can check the most suitable size of the circuit breaker for your water heater in the sizing chart below.
How to Determine the Correct Breaker Size for Your Water Heater
Let us now talk about how you can determine the correct circuit breaker size for your water heater. Here are three quick steps.
1. Check your water heater’s wattage and voltage ratings. You can look for the information on a label sticker near the water heater’s power cord base or the thermostat control panel.
If you cannot see this information, you may want to check the manual or perform a model search online.
Most water heaters have a 4500-watt element running on a 240-volt system. Commercial-grade units can have more than 5500 watts, while others can only have 3000 watts or less.
2. Determine the maximum electrical current (amperes) your water heater needs by dividing its wattage rating by its voltage.
Let us say you have a 4,500-watt water heater on 240 volts. Using our formula, you will get 18.75 amperes (4,500 ÷ 240).
3. Adjust the computed value by 125% because a water heater runs on a continuous load.
As such, we will multiply 18.75 amperes by 1.25, getting 23.4375 amperes. In other words, the size of the circuit breaker you will need for a 4500-watt, 240-volt water heater is 25 or 30 amperes.
You may think that a 20-amp circuit breaker is enough for a 240-volt, 4500-watt water heater because it only draws 18.75 amperes. Unfortunately, 18.75 amperes already account for 93.75% of the circuit breaker’s ampacity. Remember NEC’s 80% rule?
While a 20-amp circuit breaker may work, it does not guarantee your system will not trip or cause power failures. There is no way to assess how much heat the electrical wires are generating inside the cables.
Hence, getting a 30-amp circuit breaker makes perfect sense because it gives the system enough allowance to mitigate any potential problem.
What Size of Circuit Breaker Should You Use for a 5500-watt Water Heater?
A 5500-watt, 240-volt water heater requires 22.9 amperes to work. Multiplying it by 1.25, you will get a final ampere rating of 28.645. Hence, a 30-amp circuit breaker should be sufficient for this setup.
What Size of Circuit Breaker is Ideal for a 50-gallon Water Heater?
Most 50-gallon water heaters have 4500-watt heating elements. As such, 4500 watts divided by 240 volts equals 18.75 amperes. They are multiplying 18.75 amperes by 1.25 results in 23.4375 amperes. A 25-amp or 30-amp circuit breaker is ideal.
Conclusion
If you find yourself asking what size breaker do I need for a water heater, always remember the following steps.
- Determine your water heater’s voltage and wattage ratings.
- Divide the wattage by the voltage to get the water heater’s amperage rating.
- Multiply the water heater’s amperage rating by 1.25 to get the correct circuit breaker size.
How simple is that? You can use this quick formula to determine the circuit breaker size of almost any electrical appliance in your house.
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