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3-phase water heater

What is 3-phase electricity.
People are generally 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 efficiency 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
Difference between single-phase and 3-phase

3-phase balanced water heater
Larger image
3-phase balanced water heater
There are two basic types of 3 phase balanced water heaters.
One type has 3U elements, and the other type has ordinary single U elements same as residential water heaters.
3U type heaters have 1 to 5 elements, while single U heaters have groups of 3 elements. For example 3-element, 6-element, 12 element etc.

3U element is basically 3 elements in one. Single U is a single ordinary element.

Both types have 3 Hot wires that enter top of water heater. Each Hot wire supplies power to more than 1 element.
Voltage ratings for 3-phase water heaters vary from 208 to 480 volt.
3U type heaters generally us a temperature sensor to activate a contactor to turn power on-off to elements.
Single U type heaters use ordinary thermostat.

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 label that specifies single or 3-phase.

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
Homeowners sometimes have opportunity to own commercial grade 3-phase electric water heater.
Residential homes do not have 3-phase. However some 3-phase heaters can be converted to single-phase residential use, assuming certain parameters are met. The heater must be convertible, wiring must be changed, and the elements changed to match residential volt-watt rating.
Most commercial 3-phase water heaters are non-balanced and look like ordinary residential water heaters. Non-balanced means the electric power is not spread evenly over the three wires on the 3-phase circuit. 3-phase non-balanced can be converted to home-use with simple wiring change-over, and element change.

3-phase balanced water heaters have a large control box attached to front, and look distinctly different from non-balanced heaters. Balanced heaters can be converted to single-phase in many cases, but the changeover is more challenging due to significant wiring differences and possible element incompatibility.
When changing 3-phase non-balanced or balanced water heater to residential single-phase operation, pay attention to thermostat range and element rating... commercial thermostats can have very high temperature range up to 180 F that is extremely dangerous for residential home. In addition, elements can be rated with too high voltage and heater will under perform with lower residential voltages.
480 volt element Consider voltage rating on element when converting 3-phase to single phase
Image shows single U element, same as found in residential water heaters, except the element is rated 480-415 volt. Voltage and wattage are printed on end of each element.
The reason 3-phase water heater elements are different is that 3-phase power is available in many different voltages/ 208-480 volt etc. Higher voltages are more efficient but pose high risk if wiring is not handled correctly.

What happens when the element is rated for 480 volts and 4000 watt, and you connect household 240 volt??? Nothing serious... the element burns cooler at 2000 watts instead of 4000 watts... so you need two new elements rated for the voltage you are using.

Read more about 3 phase
Read about how to figure conversation element voltage
How to replace element

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
3-phase water heater amp chart Water heater amp chart
Single-phase 208-240-480 volt requires larger breaker for higher amps than 3-phase 208-240-480 volt.
Lower voltage also requires larger breaker than higher voltage.
Breaker must match expected amp rating.

Note: each water heater element has volt and watt rating printed on end of element. Element voltage rating must match incoming voltage. If element voltage rating is lower than incoming voltage, then element will burn out. If element volt rating is higher than incoming voltage, then element will burn cooler and amount of water heated per hour is less.

3-phase unbalanced amps.
Unbalanced 3-phase load: leg1=28.8 amps. leg2=28.8 amp, leg3=50  amp
50 x √3 (1.732) = 88.8
3-phase ratio is √3

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

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 heater Timer for 480 volt water heater
Illustration shows plan for connecting timer to 3-phase water heater

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