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Electrical Wire and Cable

The Right Wire and Breaker for an Electric Water Heater

What is the right circuit breaker and cable for an electric water heater? This electrical wiring project is about the Electrical Wiring for a Water Heater in a Home.


Wiring for an Electric Water Heater
Electrical Question: What is the right circuit breaker and cable for an electric water heater?

My electrical wiring project involves Change the Wiring a Water Heater in the Bathroom of a Mobile Home.

This electrical wiring question came from John, a Handyman in Fairfield, Ohio.

Additional Comments: Professional.

Dave’s Reply:
Thanks for your electrical wiring question John, the following will assist you with your electrical question.

Wiring for a 240Volt Electric Water Heater

Application: Wiring a Water Heater.
Skill Level: Intermediate to Advanced – Best performed by a Licensed Electrical Contractor, or Certified Electrician.
Electrical Tools Required: Basic Electricians Pouch Hand Tools, Voltage Tester, and appropriate Safety Gear.
Estimated Time: Depends on the personal level experience, ability to work with tools, install electrical circuit wiring, and the available access to the project area.
Electrical Safety: Identify the electrical power source to the Water Heater, turn it OFF and Tag with a Note before working with the electrical wiring.
Electrical Wiring Parts and Materials: Electrical parts and materials for the Water Heater should be approved for the specific project and compliant with local and national electrical codes.
Electrical Codes and Inspections: Installing or changing home electrical wiring should be done according to local and national electrical codes as adopted in Fairfield, Ohio. A permit and inspections may also be required.

Electrical Wiring and Circuit Breaker for a Water Heater

This electrical wiring project is about Changing the Wiring for a Water Heater in a Home

I agree with you that this water heater circuit is not a typical configuration, and the common circuit for a new home is #10 copper wire protected by a 2pole 30amp circuit breaker, however lets look at this application carefully.

First, lets start with the NEC Code for this Water Heater Application
You have stated that the calculated amperage load for 4500watt at 240volts is 18.75amps, however NEC Article 422.13 states that the minimum circuit rating for a water heater must be 125% of the rated load, so this 4500watt load requires a minimum circuit of 23.44 amps at 240volts.

Now lets consider this Water Heater Circuit Installation
The type of insulation of the existing #12 cable should be identified and compared to the NEC wire Table 310.16 to see what the allowed ampacity of the cable is, because that is one of the main factors that will determine the amount of heat that is allowed for that type of insulation.

Based upon this information, the existing circuit breaker should be replaced with one that is correct for the existing installation. This way you are sure to protect the wire gauge of the circuit. For example: If the existing cable is 12/2 Type-TN Copper with TW or THW insulation then a 2pole 25amp breaker would be correct.

If after replacing the circuit breaker it is found that the water heater trips the breaker then the circuit wiring and breaker should be increased and replaced, as long as the water heater is working properly and without fault.

In Summary
From the information you have provided and what the NEC code states, careful consideration should be given to installing the right circuit breaker as soon as possible for the right level of protection for this circuit.

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