Turn off the power before wiring any of these systems. Although all voltages are dangerous, the 240-volt systems can cause the most harm. Take extra precautions by using electrical gloves while working on the system.
Open the junction box using the screwdriver to uncover the terminals in the heater system. Within the junction box, there are two terminals, the live and the neutral, with screws at the holes where the wires are fitted. Next to the terminals there is a screw where the ground is connected.
Strip the wires on both ends of the cable. Connect the live, neutral and ground wires to the corresponding terminals on the power source, marked respectively as "L," "N" and "G." The live wire is red, brown or black, while the neutral wire is either white or grey. The ground is green, yellow or green-yellow, or it's simply bare.
Join the live wire to one of the terminals on the heater junction box. The two terminals are used interchangeably, so you may connect the live wire to any of these. Join the neutral wire to the second terminal and then screw in both wires firmly. Connect the ground wire to the ground terminal and screw it in firmly as well.
Wrap any naked part of the wires using electrical tape to prevent a short circuit in the system. Replace the junction box cover and ensure that the cable passes through the hole meant for it. If the cable does not pass through this space, you will have trouble sealing up the junction box tight. This can be dangerous, as this part is usually waterproof.
Make sure that there is water in the container before turning the power on to use the heater. If the heater is for heating rooms or for pest control, then it is safe to turn on the power to the heating system.