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How to Wire 3-Phase Simultaneous Water Heater Thermostat?

Three Phase Continues Unbalanced Dual Element Electric Water Heater Thermostat Wiring

In our popular electric water heater wiring installation series, we will show three phase unbalanced and simultaneous electric heater thermostats and heating element wiring (480V and 415V AC) in today post.

Difference Between 3 Phase Balanced and Unbalanced Water Heater

  • Balanced 3 Phase Water Heater:

In balanced three phase wiring, all the hot wires (lines) carry equal supply (same magnitude of current and voltage). In case of star connection, the neutral carry zero current acting as a return path for current.

  • Unbalanced 3 Phase Water Heater:

In this wiring, a single hot wire (line) provides supply to both heating elements through heater thermostat. The sum total of neutral point is not zero i.e. it carries the net unbalanced current.

3-Phase Unbalanced Simultaneous Water Heater Thermostat Wiring

Simultaneous or continuous means both the upper and lower thermostats and heating elements are operational at the same time and doesn’t depends on each other as separate three phase supply has been provided to each heating element.

Keep in mind that both the lower and upper thermostats are ECO-protected i.e. both are same. In this wiring connection, the Line 1 (Red) is connected to the L1 and L3 terminals of upper and lower thermostats respectively. Line 2 (Yellow) and Line 3 (Black) are connected to the L3 of upper thermostat and L1 of lower thermostat respectively.

Upper heating element is connected through L4 and T2 terminals of upper thermostat and lower heating element is connected through L4 and T2 terminals of lower thermostat.

This way, both heating elements are operational at the same time. The same wiring diagram can be used for three phase 480V AC (US – NEC) or any other three phase supply and 3-Phase 415 V AC (UK & EU – IEC). Note that we have used red, black and blue for three phase hot lines for illustration purpose only. You may follow your regional electrical codes and wiring colors.

Three Phase Simultaneous Unbalanced Dual Element Electric Water Heater Thermostat Wiring

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Wire and Breaker Size for Three Phase Electric Heaters

In our wiring tutorial, we have used 6 gauge wire for each hot wire. You may use the appropriate cable / wire and circuit breaker according to the heater rating. Check the user manual and nameplate data printed on thermostat and heating elements.

Element WattagePhases

Circuit Breaker Size (Amp)Copper Wire Size in Gauge
3000W120 A20 A15 A15 A12121414
320 A20 A15 A121214
3800W125 A20 A1010
4000W125 A25 A20 A15 A10101214
325 A25 A15 A101014
4500W130 A25 A25 A15 A10101014
330 A25 A15 A101014
5000W130 A30 A25 A15 A10101014
330 A30 A15 A101014
5500W135 A30 A25 A15 A8101014
335 A30 A15 A81014
6000W140 A35 A30 A20 A881012
335 A30 A15 A81014
8000W150 A45 A40 A25 A88810
345 A40 A20 A8812
9000W150 A45 A25 A8810
350 A45 A25 A8810
10000W150 A30 A810
350 A25 A810
11000W150 A30 A810
350 A25 A810
12000W135 A8
330 A10

Three Phase Wiring Color Codes – NEC & IEC


Three Phase 480 AC:

Black = Phase 1 or Line 1, Red = Line 2, Blue = Line 3, White / Gray = Neutral and Green/Yellow = Earth Conductor


Three Phase 415 AC:

Grey = Phase 1 or Line 1, Black = Line 2, Brown = Line 3, Blue = Neutral and Green = Earth Conductor

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  • Disconnect the power before replacing, repairing, troubleshooting, maintenance and installation electrical appliances and equipment.
  • Use the proper size of cable and wire by following this simple calculation method (How to determine the suitable size of cable for Electrical Wiring Installation)
  • Failure to do so can result in electrical shock, serious injury, fire or even death.
  • Please follow the manual instruction, local area codes or contact a licensed electrician for proper installation.
  • The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.

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  1. Cedric Ainscough says:

    Could you please send on any regulations for solar panels for the Irish markets

  2. Azmat Janjua says:

    Like to get more information on Pump controls.

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