Foundation · Unit 2
Electricity for heating controls
In short
The colours and sleeving, the fused spur, permanent and switched lives, why every load needs its neutral and its earth, cables and terminations, Boiler Plus and the interlock, and polarity - why it is tested and what the readings say. Each lesson is proved on a circuit.
Comes after Reading a circuit.
In this unit
The colours, and sleeving
Brown, blue, green-and-yellow; the old colours; a switched live in a black core, sleeved brown.
How it opensLook at the canvas: a fused spur, a changeover switch and a lamp. In this lesson you wire them, and learn what the colours of the wires mean.
The fused spur
The fused connection unit (FCU): its 3 A fuse, its double-pole switch, the point of isolation. Proved on with the meter, and off.
Permanent and switched lives
Two lamps: one on a permanent live, one on a switched live, read with the meter as the switch makes.
Every load needs N and E
A boiler with a live and nothing else: live but dead. Then its neutral, then its earth, each proved.
Cables and terminations
Twin-and-earth to the wiring centre, the valve's own flex and what each core does, strain relief, ferrules.
Boiler Plus and the interlock
What a new boiler must have, and the interlock: the boiler fires only when a control calls, proved on a small circuit.
Polarity, and why it is tested
A boiler with its live (L) and neutral (N) crossed, and the two readings to earth that show it. Put right, and proved with three readings.
You will learn to
- Name the colours a core may typically carry, old and new, and what brown sleeving says
- Explain the fused spur: 3 A, double pole, the point of isolation
- Tell a permanent live from a switched live with the meter
- Explain live but dead and NO EARTH, and give every load its L, N and E
- Choose twin-and-earth or heat-resistant flex, clamp the sheath, fit a ferrule
- Say what Boiler Plus asks of a new boiler and what the interlock is
- Test polarity at a boiler and read a reversed supply from L-E and N-E
Checks and credit
- A timed check at the end of the unit, its questions drawn at random. The score goes on your record.
Where it connects
The parts it uses
Foundation
- Reading a circuit
Unit 1, before this one
- Safe isolation and the earth
Unit 3, next
Back to the Programme.
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