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What Size Breaker for Water Heater (How to Calculate)

 
 

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Most electric water heaters are wired to a 240 volt dedicated circuit, with a 30 amp double pole breaker. But this doesn't tell the whole story, and there are no absolutes. So asking what size breaker for your water heater is an important and worthwhile question.

This article will cover how to determine which size breaker your electric water heater requires, and explain the important role breakers play in your home. In addition, we'll also answer some frequently asked questions.

Calculate The Correct Breaker Size For Your Water Heater

What Size Breaker for a 50-Gallon Water Heater?

Although, many homeowners ask: "What size breaker do I need for a 50-gallon water heater?"

In reality, the size of the tank doesn't matter.

The correct question to ask is: "What size breaker do I need for a 4500 watt water heater?"

In order to determine the breaker size, you need to know the wattage and voltage rating of the water heater. We'll cover this below.

What Size Breaker Do I Need for a 50-Gallon Water Heater?

Many 50-gallon water heaters use 4500 watt heating elements, if this is the case with yours, then your electric water heater will require a dedicated 240-volt, 30-amp breaker. 

How To Calculate The Correct Breaker Size For Your Water Heater

Sizing a Breaker for Your Water Heater

Sizing is a fancy way of saying: 'determining the right size breaker for your water heater'. Although, not hard, there are a few steps in the process.

Here's a few basics to know about water heater breakers:

  • Electric water heaters must be hardwired to a circuit breaker in your electrical panel
  • If the incorrect sized breaker is used, you run the risk of not only damaging your water heater, but also creating a serious safety issue
  • NEC Code requires the circuit breaker be sized at 125% of the intended load. Simply put, you'll need to purchase a circuit breaker that can handle 25% more electrical load than the water heater requires
  • It must be a dedicated breaker, which means it can not power any other appliances or outlets other than the water heater
  • It must be a double pole breaker

Why is a Double Pole Breaker Required?

A double pole breaker is required for water heaters in order to isolate the voltage. Since the majority of electric water heaters use between 220 to 250 volts, there's power coming in on both leads to the unit.

If a single pole breaker was used, there would be live wires in the water heater, feeding through the heating elements.

The double pole breaker has two hot wires connected by one neutral wire. So, if there's a short circuit on either of the hot wires, both will trip and shut down the water heater.

How to Determine the Right Sized Breaker for Your Water Heater

There are 3 steps to determine the breaker size for your water heater:

Step 1 - Gather Information

First, you need to find the water heater's wattage and voltage ratings. 

If you no longer have your manual, you can typically find this information on a label sticker attached to the tank, or on the thermostat's control panel.

If you still can't find the wattage and voltage ratings, you can do a quick Google search with the manufacturer name and model number of your water heater.

Step 2 - Calculate the Load

Next, you need to determine the maximum Amps required for your water heater. The equation is simple:

Watts ÷ Volts = Amps

As an example, if your water heater has a wattage rating of 4500 and a voltage rating of 240, it will require 18.75 Amps.

(4500 Watts ÷ 240 Volts = 18.75 Amps)

Step 3 - Calculate the Breaker Size

Finally, multiply the Amps by 125% (NEC Code). This will determine the correct sized breaker for your water heater.

So, following along with our example, multiply 18.75 Amps by 125%.

(18.75 Amps x 125% = 23.43 Amps)

For a 4500 watt 240 volt water heater, you will need a 25 or 30 Amp circuit breaker. The majority of electricians will recommend installing a 30 Amp breaker to allow for electrical fluctuations.

We highly recommend hiring a professional to make any adjustments to your electrical panel.

FYI

  • Electric water heaters use between 220 to 259 volts of alternating current
  • Most electric water heaters require a 20 or 30 Amp double pole breaker. (The breaker must be rated for the power draw of the water heater)
  • The wire gauge size is determined by the amperage drawn by the water heater
what is the right circuit breaker size

Frequently Asked Questions

Do you still have questions? Here are a few frequently asked questions:

How Does a Circuit Breaker Operate?

The circuit breaker allows the electricity to pass through when the electric current is below the circuit breaker rating. However, the circuit breaker will "trip" when the electric current flows above the rating of the breaker.

When the breaker trips, it disconnects the flow of electricity to the water heater, protecting it from damage.

What Size Wire Do I Use?

The wire gauge (size of the wire) is determined by how may Amps will be running though it.

240 volt electric water heaters use a 30 Amp breaker, so they should be wired with 10 gauge wire.

Is it Okay to Use a Bigger (or Smaller) Breaker?

No, you should always use the right sized breaker for the appliance.

If the breaker is too big (higher amperage than necessary), it will not protect your water heater should it overload or short circuit. The breaker will not trip, and could result in damage to your water heater or even a fire. 

If the breaker is too small (lower amperage than needed), the circuit breaker will frequently trip. Not only is this annoying, but the constant on and off operation could cause damage to your water heater.

Why is My Water Heater Circuit Breaker Tripping?

If your water heater's circuit breaker is tripping, we highly recommend hiring a hiring a professional plumber to assess the situation. More often than not, there's a short circuit within the water heater that's causing it to pull too much current.

Another possible reason is that your water heater wasn't properly installed. If your water heater isn't on a dedicated circuit, or the circuit is too small it will overload and trip the breaker. Contact an electrician to troubleshoot and resolve the situation. 

Dangers to Having the Wrong Sized Breaker

There are 3 basic dangers to having the wrong sized breaker:

  • Risk of fire
  • Risk of damaging the water heater
  • Risk of damaging the electrical panel

My Water Heater Has Two 4500 Watt Elements, Do I Calculate 9000 Watts?

No, even though your water heater has two 4500 watt heating elements, both are never working at the same time. When the top element turns ON during high hot water demand periods, the bottom element turns OFF.

Since only one of the 4500 watt heating elements is working at a time, you will use 4500 watts to calculate the breaker size.

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