How to Connect a Hot Water Tank to a Generator

An electric generator produces alternating current (AC) that can be used to provide electricity for household appliances.

Hot water comes from an electric generator.Hot water comes from an electric generator.
An electric immersion heater installed in a domestic hot water tank can be powered by a generator. The voltage of the heating elements must be the same as that produced by the generator, and the generator must produce enough electrical power to operate the immersion heater. Domestic hot water tanks often have two heating elements and both of these must be connected to the generator.

Remove the covers on the immersion heaters installed in the hot water tank. Look at the numbers shown on the base plate and read the power of each heater in watts. Note what voltage they are designed for. Many immersion heaters will be 230 volts and will take several kilowatts (kW) of electrical power. Calculate the current taken by each immersion heater. For example, if each heater is 3.0 kW, divide this power in watts by the voltage in volts to obtain the current in amps. First multiply 3.0 kW by 1,000 to get watts, then divide by 230 volts. This calculation gives a current of 13.0 amps.

Look at the front panel of the generator. Many generators have outlets for both 230 and 115 volts. Check if the 230-volt connection takes a standard plug or if it is a special type of plug. Check the manual for the generator and find the rated power of the generator in kilowatts.

Install a junction box and two circuit breakers close to the tank if the hot water tank has two heating elements. Measure the length of the cable you will need to connect the generator to the junction box, and the cable needed to connect the junction box to the immersion heaters mounted in the water tank.

Purchase a junction box with the circuit breakers and enough cable to make all the connections from an electrical supply store. Get the correct 3-wire cable rated for the current being carried by the cables. Buy the right kind of plug to connect up to the generator.

Install the junction box and the circuit breakers close to the hot water tank. Connect the wires from the junction box to the terminals on the water heaters making sure the ground wires are firmly connected. Put the covers back on the heating elements so that no wires are exposed. Connect the cable running from the generator to the junction box.

Switch the circuit breakers to the "off" position, start up the generator engine. Switch on the generator power. Go to the junction box and switch one of the circuit breakers on. The generator noise should change slightly as it provides power to the first heating element. Then switch in the second element and check that the generator is running normally.

Things You Will Need

  • Measuring tape
  • Junction box
  • Circuit breakers
  • 3-wire cable
  • Basic tools


  • If the power of the generator is given in kilovolt-amps (kVA), use this number as approximately equal to the power of the generator in kilowatts (kW).


  • Always be careful when connecting up 230-volt circuits. If in doubt, ask a qualified electrician to check out the circuit and the installation of the junction box and circuit breakers.

About the Author

Peter Johnson has managed development programs in Africa and the Caribbean since 1985. Focusing on community management of natural resources, renewable energy and sustainable economic development, he has worked in Djibouti, Sudan, Egypt, Mali, Madagascar, Guinea and most recently in Haiti. He has postgraduate degrees in chemical engineering and fuel technology, as well as protected landscape management.