3-phase water heater

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There are 2 general categories of 3-phase water heaters:
1) Light duty 'non-balanced' heaters with two heating elements that do not pull equal power from each of the 3 Hot wires, and can be re-wired for single phase if needed. Typically 30 to 100 gallon size. Mechanical thermostats.
Dura power Spec sheet, 208-480 volt unbalanced.pdf

2) Heavy duty commercial 'balanced' heaters, available with numerous elements, and high wattages, where each element pulls equal, or balanced, power from each of the 3 Hot wires.
Heavy duty heaters are available in larger sizes, 150 to 2500 gallon. Mechanical or electronic thermostats depending on manufacturer.
Dura power Spec sheet, 208-480 volt 3-phase balanced .pdf

What is 3-phase electricity.
People are more familiar with single-phase residential wiring where two wires are required for each circuit ... plus a ground wire.
Residential voltages are typically 120-240 volt AC.

3-phase is not available for residential homes because 3-phase wiring is more complex.
3-phase requires 3 wires to complete a circuit (plus ground wire) and is available for commercial factories, schools, buildings, and businesses.
Why use 3-phase? 3-phase delivers higher average power vs single phase, and is more efficient for motor loads and large area uses ... and for heating water.

3-phase offers voltage choices including 120, 208, 240, 277, 380, 480, 600 volt depending on electric service.
3-phase service also gives options for single-phase 120, 208, 240, 277, 380, etc, plus wide variety of other voltages using buck-boost transformers.

Unlike single-phase residential electricity, 3-phase usage at a commercial building must be balanced so equal work is done by each of the 3 Hot wires. This page talks about balanced and non-balanced 3-phase water heaters.
Overall, 3-phase is more complex than residential single-phase because of the third wire and because usage must be balanced, while single phase uses less wire and balancing is not a major problem since residential loads are generally much smaller than commercial.
Resource:
What is 3-phase
Difference between single-phase and 3-phase
What is 208 volt
What is 277 volt
What is high leg delta
Illustration

Balanced 3-phase commercial water heaters All water heaters have rating label that specifies the brand and type heater and whether it is single phase, typically shown as Ph 1, or 3-phase, typically shown as the abbrevation 3Φ. Balanced means each of the 3 hot wires from 3-phase line are providing same amount of power. Balanced 3-phase is important in commercial applications so motors run correctly without power loss, so having balanced water heater will not cause imbalance issues elsewhere in facility. AO Smith heavy duty Dura Power series range from 150 gallon to 2,500 gallons ... and 144 kW (144,000 watt) to 900 kW (900,000 watt) with voltages that include 208, 240, 480, 600 volt single or three-phase ... and international voltages 380 and 415.. The heavy duty Dura Power heaters have 1 to 24 heating elements, each element rated 15,000 watt to 18,000 watt. Contrast with ordinary residential heater with two 4500 watt elements. The heavy duty Dura Power heaters range in size from 150 gallon at 65"x32" up to the 2500 gallon vertical square heaters (with a round tank inside) that are 12' high and 7' wide, with twenty-four 18,000 watt elements that draw 1,200 amps at 208 volt, and 520 amps at 480 volt. Cement lining is an option vs anode rod. Typically, the cement-lined tanks don't need anode rod since the liner prevents rusted tank, however is not assumed to be better since anode rods can generally be replaced periodically to maintain investment. Resources Spec sheet 3-phase balanced .pdf Installation-service 3-phase balanced .pdf
	Example 3-phase balanced heater with 9 elements Note there is a choice between electronically-controlled heater and older style heater with mechanical thermostats. The electronic heater uses circuit board and user interface that shows status and error monitoring, plus offers precise temperature control via the thermostat probe. Electronic type heater might notify if one element was burned out, or if one leg of the 3-phase power drops out, and might offer interface with building management software such as AO Smith's iComm. Disadvantages of electronics might include, vulnerability to surge or power fluctuations, and increased cost of repairs if circuit board or user interface fails. Contrast with the simpler design that uses ordinary mechanical bi-metal thermostats (same as found on residential heaters, except maybe higher temperature range). Advantages could include, easy and less expensive repairs, not vulnerable to surge or power drop. Disadvantages would include approximate temperature control, lack of diagnostic error messages ... so no easy way to discover if an element or thermostat has failed, or blown a fuse, or melted a wire etc. The mechanical 3-phase heater can be converted to single phase, while my guess is, the electronically-controlled model cannot. Resources: Example service manual .pdf

Larger image 3-phase balanced water heater There are different types of 3 phase balanced water heaters. Some have 3U element ... 3U element is basically 3 elements in one. Others have ordinary single U elements, same as found on residential water heaters. Single U is a single ordinary element. With the single U type heater, there are electronically-controlled models and mechanically controlled, depending on type of thermostat. Other choices include the kW rating of heater, or the number of single U elements that are installed.. Illustration on left shows mechanically controlled heater with 3 ordinary thermo-o-disc thermostats, 3 single U elements installed, and 3 element openings that are plugged. The thermostats are ordinary therm-o-disc or Aprom thermostat that is rated up to 480 volt. Each thermostat controls 1 element by reading tank temperature through tank wall. Mechanical thermostat settings and temperature calibration are approximate. How to wire thermostats for residential water heater Three-phase electric water heaters are more efficient when fully balanced. Non-balanced heaters discussed below are less efficient than balanced. Resource: 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 Commercial grade 3-phase balanced install & service manual Commercial grade 3-phase balanced installation manual

Water heater amp chart Every circuit requires a circuit breaker (overcurrent protection) to ensure the wires are not exposed to overamperage that will melt wire, cause fire etc. Circuit breaker must match expected amp rating. Wire must be approved 600 volt ... and wire must match amp rating of breaker. The amperage table posted below, shows that 3-phase can use a smaller size breaker than single-phase to deliver the same Kw (power) ... Why? Because 3 hot wires from 3 phase can deliver the same kilowatts (Kw or power) with less amp consumption than 2 hot wires with single-phase. The dynamics of electric power generation can be compared with a bicycle. Single-phase is like a 2 legged bicycle, but when both pedals are briefly at the top and bottom at same time, the power drops to zero. Three phase is like a 3 legged bicycle where no two pedals are at top and bottom at same time, so power never drops to zero, and 3 phase delivers smoother, higher power than single phase. Resources: 3-phase generation Difference single-phase and 3-phase Less amp consumption from 3-phase means less heat on the wire, and less heat means increased efficiency. It also means 3-phase can use smaller breaker and smaller size conductor (wire) than single phase for the same power output. Increased efficiency and using smaller wires lower the cost which is the reason 3-phase is used for commercial applications. ++++ 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.

Larger image Balanced and unbalanced element wiring -Unbalanced 3-phase water heater means 1 leg (wire) supplies Hot to both elements. -With unbalanced heater is wire for non-simultaneous, both elements are never ON at same time. One element is on or other element is on, or both elements are off. So one leg of the 3-phase is ON when either element is heating. Other two legs alternate ... and are ON depending on which element is heating. If unbalanced heater is wired for simultaneous operation, where both elements could be ON at same time .... 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 always √3 Balanced means equal draw from all three Hot legs in 3-phase circuit. The illustration shows a Balanced 3U heat element that has 6 wires, and 3 heating loops. The 3 heating loops do the job of 3 single U elements. Each leg draws same amps, or balanced amps. Each leg supplies power to one side of two different elements in the 3U. -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.

Water heater should specify WYE or Delta
Delta and WYE are types of 3 phase service, that depend on how power company wires the transformers that supply power to the commercial building.
Resources
What is 3-phase high leg delta
What is 208 volt wye

Illustrations on left show 3U elements. Not every 3-phase water heater heater has 3U elements.
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 hot wire leads:
Can be used for 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 hot wire leads:
can be used for 3-phase wye only
Buy
3U elements at Amazon

Example 3-U 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.

	Example 3-phase thermostat wiring on heater with 6 single U elements Elements are shown as R1, R2... R6 Single-phase thermostats T open-close 2 different 3-pole contactors (in yellow) 3-pole Contactors open-close 3-phase power going to element(s)
	Timer for 480 volt water heater Illustration shows plan for connecting timer to 3-phase water heater Buy: Mars 2-pole and 3-pole contactors at Amazon 480V WG736 clock motor at Amazon T104 timer Resource: How to wire 3-phase timer How to wire 3-phase

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 can be identified by a large control box attached to front. They can appear 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.

Caution:
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, a temperature 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.

Larger image	3-phase non-simultaneous Unbalanced Both elements are never ON at same time. Always use ECO-protected thermostat on upper and lower Elements will heat with any applied voltage Each element has volts and watts listed on side. Volts squared divided by watts = correct ohm rating to test if element is good. 3-phase water heater service manual Buy commercial grade 3-phase thermostat for 3-phase non-balanced water heater Camco 120F to 180F thermostat with reset button at Amazon (commercial grade only) Thermostats for residential water heater 90F to 150F at Amazon Identify unbalanced water heater: it looks just like ordinary tank-type heater and does not have metal large box with contactors attached to front of unit. 3-phase balanced water heater has large box attached to front of unit. Unbalanced means that 1 leg of the three phase carries greater load than other two legs. So this is just ordinary single-phase water heater except few wires moved so there is a 3-wire connection on top of unit. Difference is that 3-phase non balanced will usually have larger wires and breaker and elements. Unbalance water heater uses ordinary 2-pole element and thermostat, except thermostat can be rated for 40 amps at 240Volts, and 30 amps at 480 volts Ordinary hardware store thermostats are rated 30 amp at 240V. 3-phase thermostat at Amazon 40 amp 240V thermostat at Amazon pdf file see page 7 Balanced load, means all three legs carry equal load. Balanced water heater uses element with connections for 6 wires. Illustrations for balanced: see lower on page
Larger image Another image slightly different wiring: larger	3-phase simultaneous Unbalanced. For example: L2 50 amps, L1 and L3 29 amps, depending on each element etc Compare with non-simultaneous shown above: Move Red wire from T4 on upper thermostat to L1 on upper thermostat Either element can turn ON, as temperature varies top and bottom of tank Always use ECO-protected thermostat on upper and lower Elements will heat with any applied voltage Each element has volts and watts listed on side. Volts squared divided by watts = correct ohm rating to test if element is good. 3-phase simultaneous current load Heavy-duty commercial water heaters: Balanced 3-phase Commercial electric water heater troubleshoot Commercial electric water heater part diagnosis 3-phase electric water heater manual
Larger image	Convert 3-phase non-balanced water heater into single-phase water heater 3-phase converted to single phase non-simultaneous Unbalanced Compare with non-simultaneous shown above: Move Yellow wire from L3 on upper thermostat to L2 on wiring connections Connect single-phase power to L1 L2 3-phase wire size chart Ordinary electric water heater can run on any voltage (excluding volt/amp ratings below amount needed to heat tank of water, for example typical 12 volt battery will not heat tank of water). Resistance elements are like light bulbs. Any voltage will work. Less voltage means dimmer bulb. Read more in section below. Voltages include single-phase, split phase, and 3-phase residential/commercial voltages with either 50 or 60 Hz. You can also rewire tank as if it is ordinary non-simultaneous See image

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

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

		3 phase simultaneous water heater converted to single phase simultaneous 1. Open panels on water heater and make drawing of wires 2. Note wire colors... wire colors vary... but the conversion is same 3. Do you want simultaneous operation? Where both elements have power? Illustration on left shows simultaneous. Simultaneous operation for ordinary household usually means that you have 60 amp breaker and 6 gauge wire See illustration below for non-simultaneous conversion 4. Note how many screws are on right side of upper thermostat If you want simultaneous, the 2 screws on right side of upper thermostat are ok. If you want non-simultaneous, then 3 screws on right side of upper thermostat are needed.... so change thermostat.
		3 phase simultaneous water heater converted to single phase NON-simultaneous Change the upper thermostat to a thermostat with 3 screws on right side of thermostat

	Consider voltage rating on element when converting 3-phase to single phase Typical 3-phase water heater is available to meet many different voltages/ 240 volt/ 277 volt/ 480 volt etc Voltage and wattage are printed on end of each element.
	Consider voltage rating on element when converting 3-phase to single phase 3-phase water heater elements are often higher voltage. The reason is that 3-phase power is available in many different voltages from 208-480 volt. Higher voltages are more efficient but pose higher risk when wiring is not handled by professional electrician. 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... In this situation, you need two new elements rated for 240 volt. Resources: Read more about 3 phase Different between single-phase and 3-phase Read about how to figure conversation element voltage How to replace element
	Consider temperature rating on thermostat when converting 3-phase to single phase Typical 3-phase water heater is available to meet very hot applications (140°F+) for applications such as commercial kitchens and laundry where sterilization is objective These temperature can injure and kill people. 120° can scald in less than 1 minute, 140° in less than a second. Typical household water heater thermostat is set at 120-125°F. Typical bath-shower is 104-108°F Change thermostats to residential 90-150° range, and avoid commercial 180° thermostats ... scroll to top of this page to identify thermostats Buy: Water heater thermostats at Amazon Resources: How to change thermostat

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