Power Supply
Immersion Spur (the immersion heater's own supply)
In short
The same fused connection unit (FCU) as the Fused Spur, on a silver plate marked 3 kW. Its terminals: L, N, E.
If this is your home: this page is written for heating engineers. Mains wiring and gas appliances are not DIY jobs; call a Gas Safe registered engineer. If you smell gas, leave the building and call the National Gas Emergency Service on 0800 111 999.
What it is
The same fused connection unit (FCU) as the Fused Spur, on a silver plate marked 3 kW. It feeds an IMMERSION HEATER: an electric element that heats the water in the hot water cylinder.
A 3 kilowatt (3 kW) immersion heater draws about 13 amps (13 A). So this spur has a 13 A fuse, and a circuit of its own from the CONSUMER UNIT, the home's fuse box.
It is never fed from the heating controls' 3 A spur.
Terminals
| Terminal | What it is for |
|---|---|
| L | The live (L) out to the immersion heater. It runs through one side of the switch, then through the 13 amp (13 A) fuse. |
| N | The neutral (N) out. It runs through the other side of the same switch. |
| E | The earth (E) out. It goes straight through: it is never switched and never fused. |
What the meter reads
Switched on, its live (L) and neutral (N) feed the immersion heater's flex.
On site the earth is never switched. In this simulator the spur is the supply itself: switched off, it gives no live, no neutral and no earth. The earth path is still there: with the power off, a continuity test proves it.
Switched off, the immersion heater is dead, and the heating controls keep their own supply. So there are two supplies and two POINTS OF ISOLATION: switch off both before work on the cylinder.
Where it connects
Lessons that use it
- An immersion heater on its own circuit
Intermediate · Protection and extras
Also in power supply
Practise it in the simulator.
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