Cables
Flex (2, 3, 4 or 5 cores)
In short
Flex is a round, flexible cable: stranded cores in one sheath. Each core is made of many thin wires, so it bends easily.
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
FLEX is a round, flexible cable: STRANDED cores in one SHEATH. Each core is made of many thin wires, so it bends easily.
It makes the last connection to a part that stays cool: from the wiring centre to a room thermostat (stat), a programmer or a receiver. A part that gets hot takes heat-resistant flex.
On the canvas it comes short, with its cores loose at both ends.
- Take a core with the Wire Tool, and click a terminal inside its reach. When both ends of a core are on terminals, that core is a wire.
- The Wire Tool also drags an end or a bend by its handle, and drags the sheath to move the whole cable.
- Bend adds a bend.
- Erase lifts a core off its terminal, or cuts back one that is not needed.
What the meter reads
A core with both ends on terminals reads continuity from end to end, dead.
A core with one end loose joins nothing, so it carries nothing.
Brown and blue may typically be the live (L) and the neutral (N). Green-and-yellow is the earth (E). In a 4-core or 5-core flex, the black and the grey may typically be switched lives.
Where it connects
Lessons that use it
- Cables
Foundation · Using the simulator
- Weather compensation
Intermediate · Protection and extras
- Wiring an OpenTherm room thermostat
Intermediate · Bus controls
Practise it in the simulator.
Runs in the browser on a laptop or desktop. Cancel any time.