Foundation · Unit 1
Reading a circuit
In short
Read before you wire: the words and why they are what they are, a circuit from source to return, COM / NO / NC on a switch, a thermostat as a switch, the back of a programmer, a valve, and a manufacturer's diagram against the wiring centre. Every reading proven with the meter.
In this unit
The words, and why they are what they are
Every word of heating wiring, one at a time, each on the part it lives on.
A circuit: source, path, load, return
Wire a lamp to a fused spur and prove it with the meter. Then take its neutral away: the lamp goes dark, but it is still live.
How a switch works: COM, NO and NC
A changeover switch with a lamp on each contact: its common (COM), normally open (NO) and normally closed (NC) contacts, read with the meter.
A thermostat is a switch
A room thermostat (stat) and two cylinder thermostats are switches. One prints NO and NC beside its numbers: read the label.
The back of a programmer
A programmer's two changeover switches, fed from its live (L). Then a volt-free programmer, based on the Horstmann Diadem 425, with commons of its own.
Reading a valve
Inside a 2-port valve: the brown motor, and the end switch from grey to orange. Then the 3-port valve's cut-away.
Reading a manufacturer's diagram
A maker's numbered blocks against a wired S-Plan, block by block with the meter. A wiring centre's blocks are only plain conductors.
In the simulator, you practise how to
- Say what live, neutral, earth, switched live, demand, call, satisfied, COM, NO and NC mean
- Follow a circuit from the source through the load and back, and prove each part of it with the meter
- Read a changeover switch: which contact is made at rest and which when it operates
- Read a thermostat as a switch, on a room stat and two cylinder stats
- Read the back of a programmer: two changeovers from L, or volt-free with its own commons
- Read a valve: the motor, the end switch and the orange that comes out of it
- Read a manufacturer's diagram against the wiring centre's blocks
Checks and credit
- A timed check at the end of the unit, its questions drawn at random. The score goes on your record.
Certificates of completion and credentials are DrawWarm’s own. They record practice and tests in the simulator. They are not a formal (regulated) qualification, and they do not show that anyone is competent to work on a heating system.
Units based on makers’ products
The units in these lessons are the simulator’s own, simplified for teaching. Each is based on a maker’s product and may differ from it: on site, read the unit’s own instructions.
- Based on the Horstmann Diadem 425
Makers’ names and model numbers are trade marks of their owners, used only to say which product a unit is based on. DrawWarm is not affiliated with, or endorsed by, any maker named on this site.
Where it connects
The parts it uses
Wiring diagrams
Foundation
- Using the simulator
Unit 0, before this one
- Electricity for heating controls
Unit 2, next
Back to the Programme.
Practise it in the simulator.
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