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3-phase water heater
What is 3-phase electricity.
Most people are familiar with single-phase residential wiring where two wires are required for each circuit ... excluding ground wire.
Residential voltages are usually 120 240 volt AC.
Three phase is different. It comes directly from the power plant and runs more efficiencly than single phase and is used for heavy amp loads like factories, schools, buildings, and businesses. Three phase requires 3 wires to complete circuit.... excluding ground wire ... and more voltages are available, such as 208, 277, 440, etc.
What is 3-phase
People often have opportunity to own commercial grade 3-phase electric water heater.
Three-phase electric water heaters are not more efficient, unless they are fully balanced and connected to commercial three-phase power.
Most commercial electric water heaters are non balanced, and have same efficiency as residential heaters. All heaters have rating lablel that specifies single or 3-phase.
Non-balanced means the electric power is not spread evenly over the three wires on the 3-phase circuit. 3-phase (non-balanced or balanced) can be converted to home-use with wiring change-over.
When installing 3-phase commercial water heater in residential home, pay attention to thermostat range and element rating...  commercial thermostats can have very high temperature range that is dangerous for residential home. Elements can be rated with too high voltage and heater will not perform as expected. lements and thermostats are generic for both residential and non-balanced, and can be replaced.
Image shows general idea: BUT 3-phase balanced Tank can be wired for single phase without removing contactors/ open .pdf to right.
Convert 3-phase balanced to single-phase
3-phase balanced water heaters have contactors that turn elements on-off.
Generally 3-phase balanced water heaters have box attached to front of heater to hold contactors
While 3-phase non-balanced and single-phase water heaters do not have box attached to front of water heater.

AO Smith 3-phase to single-phase conversion instructions/ .pdf
Convert-3-phase-water-heater-to-single-phase / pdf

How to install light duty commercial electric water heater
How-to-install-commercial-electric-water-heater /pdf
Repair and Service 3-phase balanced electric water heater  (24Mb download/ huge file)
At AO Smith - click literature tab
3-phase water heater manual

Image of amp rating chart/ jpg

Convert 3-phase to single-phase
Convert 3 phase balanced 2
Convert 3 phase balanced 3
Service manual 1
Service manual 2

Assumes 4500 watt element rated for 240V
Element wattage and voltage printed on end of each element
How to identify and replace element

Wattage drops when voltage is reduced
See water heater label showing difference between 208V - 240V
Resistive loads such as light bulbs and elements will burn less hot when voltage is reduced. Examples: ordinary household dimmer for incandescent bulbs, or power brown-out when household voltage is reduced
Formula for 240-to-120V:
.25 x 4500 watts = 1125 watts

How to choose and replace elements

3 phase water heater elements
Larger image
Balanced and unbalanced element wiring
3 phase water heater elements
Balanced means equal draw across all three Hot legs in 3-phase circuit
Unbalanced: 1 leg supplies Hot to both elements. Other two legs alternate depending if upper/lower element is on. Neither element is ON at same time. Non simultaneous.
So one leg is constantly ON when either element is heating. Other two legs are ON depending on which element is heating.

Balance heat element has 6 wires, and 3 heating loops
Elements will heat with any typical voltage

3-phase heating element
Loss of phase or failure of one element in 3-phase Delta circuit will reduce wattage output by 33%. Result 3/0 open delta
Loss of phase or failure of one element in 3-phase Wye circuit will reduce wattage output by 50%. Result 3/0 open wye.
3 phase water heater elements Water heater should specify WYE or Delta

3-phase tankless requires delta (call manufacturer)

3-phase tank-type heater can be connected to wye or delta (call manufacture- look at spec sheet- look at label on side of tank)

6 wire leads:
can be used single phase, or 3-phase delta or 3-phase wye
3-phase has A B C hot leads
Hot A connects to one leg of element 1 and one leg of element 2
Hot B connects to one leg of element 2 and one leg of element 3
Hot 3 connects to one leg of element 1 and one leg of element 3

3 wire leads:
can be used for 3-phase wye only

3-phase water heater manual p17
How to wire 3-phase
Sequence of operation 3-phase balanced before 2002
Sequence of operation 3-phase balanced after 2002

3U elements at Amazon
3-phase heating element 6 leads on each element.
Basically there are 3 elements in one.
Each of the 3 elements has 2 wires. So 6 wires total.
3-phase has 3 Hot wires arriving from breaker box
3-phase has A B C hot leads
Hot A connects to one leg of element 1 and one leg of element 2
Hot B connects to one leg of element 2 and one leg of element 3
Hot 3 connects to one leg of element 1 and one leg of element 3
Each element pulls same amps so load is balanced.
Contrast: Unbalanced 3-phase water heater has 2 ordinary elements.
Hot A feeds 1 leg of element 1, Hot B feeds 1 leg element 2
Hot C feed 1 leg of element 1 and 1 leg of element 2.
3-phase thermostat wiring Example 3-phase thermostat wiring
Thermostats open-close 3-pole contactor
Contactor opens-closes power to element(s)
timer for 480 volt water heaterTimer for 480 volt water heater
Illustration shows plan for connecting timer to 3-phase water heater

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