What wire and breaker size to use for 5000W heater

A 5,500-watt water heater rated 208 or 240V will need 10 AWG size and a circuit breaker capacity of  40A for 208V or 35A for a 240V rating. 

Water heater voltage ratings and how they affect wire and circuit breaker capacity

Your water heater may have any of the voltage ratings 120, 208, 277, or 480V. 

The current rating can be found from the formula: 

  • Water heater power rating (watts) / voltage (volts).

From the formula, a lower voltage results in a higher rated current and subsequently may require a lower wire gauge and higher circuit breaker rating.

Always confirm first whether the water heater capacity is available for the desired voltage rating (120, 208, 277, or 480V) as this affects your choice of wire and circuit breaker size.

How to calculate water heater wire and breaker size

Water heater wire size

A 5,500 W heater rated 240V has a rated current of 5500/240 = 22.91 amps. This is the heater’s minimum current rating. 

Using the wire amp rating to gauge calculator,  the recommended wire gauge is 10 AWG.

Water heater circuit breaker size

To work out the recommended breaker size, lets refer to the excerpt from NEC 2017 below.

(E) Single Non–Motor-Operated Appliance.  If the branch circuit supplies a single non–motor-operated appliance, the rating of overcurrent protection shall comply with the following:

(1) Not exceed that marked on the appliance.

(2) Not exceed 20 amperes if the overcurrent protection rating is not marked and the appliance is rated 13.3 amperes or less; or

(3) Not exceed 150 percent of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3 amperes.

Where 150 percent of the appliance rating does not correspond to a standard overcurrent device ampere rating, the next higher standard rating shall be permitted.

Since the heater is rated more than 13.3 amps (22.91 A >13.3A), then the circuit breaker rating = 22.91  x 150% =34.36 Amps. The next standard circuit breaker is 35 Amps.

Therefore a 5,500W heater rated 240V needs 10 AWG wire size and a circuit breaker of 35A.

The table below shows indicative wire gauge and circuit breaker ratings for selected water heater power ratings.

Note: This is a guide only. Always consults a qualified professional.

No.Water heater element power (W)Water heater voltage* (V)Minimum Wire gauge (AWG)Circuit breaker (A)

*Voltage ratings for the different heaters may vary. Confirm availability of the water heater in the desired voltage.

**Assumes that the circuit breaker rating is not specified. Multiply rated current by 150% to be code compliant if rated current is more than 13.3 A. If rated current is less than 13.3A, set to 20 A (NEC, 2017)

What size of wire and breaker for 30, 40 and 50 gallon water heater?

The recommended wire and breaker size will be determined by your heater’s power rating and voltage.

For 30 gallon (2,000W, 120V), 40 gallon (5,500V, 240V), 50 gallon (4,500W, 240V), the minimum wire sizes for your water heaters would be 20, 25, and 20A  respectively.

While the corresponding circuit breaker capacities would be 25A, 35A, and  30A respectively.

To find the wire and circuit breaker rating, first, check with the manufacturer or technical specifications manual for the current and circuit breaker rating for that particular model of heater.

Note: It is possible for waters with different capacities to have the same heater element power rating.

For example, both a 40 and 50-gallon water heater may have a 4,500 heater element.

The table below shows selected water heater capacities with their corresponding heater element power ratings.

Always consult your water heater’s manual.

No.Water heater volume (gallons)Water heater element power rating (watts)

You can then use the water heater element power rating to work out the wire and breaker size that is appropriate for your water heater. 

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