Residential electric water heaters are listed under UL Standard 174, Household Electric Storage Tank Water Heaters. Electrical contractors many times are also in the plumbing, heating, and appliance business.
They need to know more than how to do the electrical hookup. The following text discusses electrical as well as other data about electric water heaters that will prove useful.
All homes require a supply of hot water. To meet this need, one or more automatic water heaters are generally installed as close as practical to the areas having the greatest need for hot water.
Water piping carries the heated water from the water heater to the various plumbing fixtures and to appliances such as dishwashers and clothes washers.
The wattage ratings of electric water heaters can vary greatly, depending on the size of the heater in gallons, the speed of recovery desired, local electric utility regulations, and codes. Typical wattage ratings are 1500, 2000, 2500, 3000, 3800, 4500, and 5500 watts.
A resistance heating element might be dual rated. For example, the element might be marked 5500 watts at 250 volts, and 3800 watts at 208 volts.
Most residential-type water heaters are connected to 240 volts except for the smaller 2-, 4-, and 6-gallon point of use sizes generally rated 1500 watts at 120 volts. Commercial electric water heaters can be rated single-phase or 3-phase, 208, 240, 277, or 480 volts.
UL requires that the power (wattage) input must not exceed 105% of the water heater’s nameplate rating. All testing is done with a supply voltage equal to the heating element’s rated voltage.
Most heating elements may burn out prematurely if operated at voltages 5% higher than for which they
To help reduce the premature burnout of heating elements, some manufacturers will supply 250-volt heating elements, yet will mark the nameplate 240 volts, with its corresponding wattage at 240 volts.
This allows a safety factor if slightly higher than normal voltages are experienced.