How to wire a domestic immersion heater

Updated March 23, 2017

A domestic immersion heater is a great way to heat water in your home so you have a constant supply when you need it. Your immersion heater is wired using three connections, the same as for your dishwasher or washing machine. So long as you've wired a couple of regular plugs before, you should be able to get your immersion heater up and running in very little time, using just a few basic tools.

Get a suitable length of three-core nonmetallic 14-gauge (NM 14) cable that has a pre-fitted fused plug on one end. The cable should easily reach between the immersion heater and a wall socket, so measure the distance using a tape measure first. Your immersion heater requires high amperes, and NM 14 can easily handle up to 15 amperes. Having a pre-fitted plug saves time on wiring, and you know it's wired according to code.

Remove 5 cm (2 inches) of the nonmetallic cover off the end of the cable using wire strippers. This reveals three coloured wires; two-tone green for ground and white or grey for neutral. The third wire is the live or hot wire, and it can be red, orange or black.

Strip 1.3 cm(1/4 inch) of coloured plastic off the end of the three wires. This reveals the copper metal that attaches to the immersion heater terminals. Twist the copper wire strands using your fingers so the strands don't separate.

Remove the cover from the immersion heater. It's usually held in place with a long screw, so use a screwdriver to remove the screw, then lift off the cover. You can now see the three-wire terminal block.

Loosen the three terminal block screws. Insert the two-tone green wire under the terminal screw labelled "Gnd" or "T" and tighten the screw. Insert the grey or white wire under the terminal screw labelled "Neu" of "Neg" and tighten the screw. Insert the third live wire under the terminal screw labelled ""Pos", "Live" or "Hot," then tighten the screw.

Check that the three connections are secure. Replace the cover on the immersion heater. Secure it using the screw.

Set the temperature on the front of the immersion heater. Insert the pre-fitted plug into the wall socket and your immersion heater will start to heat your water.


If you are unsure about wiring electrical appliances, get a professional to do it for you.

Things You'll Need

  • NM 14-gauge cable with pre-fitted plug
  • Wire strippers
  • Screwdriver
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About the Author

Stephen Benham has been writing since 1999. His current articles appear on various websites. Benham has worked as an insurance research writer for Axco Services, producing reports in many countries. He has been an underwriting member at Lloyd's of London and a director of three companies. Benham has a diploma in business studies from South Essex College, U.K.