ASB Trade › Guides › Which cable to use for sockets and lighting in a flat
Which cable to use for sockets and lighting in a flat
Cross-sections of 1.5, 2.5, 4 and 6 mm², copper only, round or flat, NYM, CYKYL or H05VV-F, chased in, in conduit or in trunking: which cable to buy for each line.
Cross-section by line: 1.5, 2.5, 4 and 6 mm²
Four copper cross-sections cover a flat. 1.5 mm² is for lighting with a 10 A breaker. 2.5 mm² is for socket groups with a 16 A breaker, enough for about 3.5 kW of appliances running at once. 4 mm² is for dedicated lines to an oven, water heater or air conditioner with a 20–25 A breaker. 6 mm² is for the hob and the incoming line with a 32 A breaker.
Number of cores: sockets and earthed appliances need three (phase, neutral, earth), for example 3×2.5. Lighting also takes three cores where the fixture has an earth terminal, and two on the run from the switch to the lamp. Going a size up on sockets is not a mistake, but 4 mm² is already hard to fit into ordinary socket terminals, so groups stay at 2.5.
Copper only
At the same cross-section a copper conductor carries more current than aluminium, bends better and does not break in terminals when re-worked. New wiring in a flat is done in copper. If the building has old aluminium wiring, it is not joined to copper directly, only through terminals that keep the two metals apart.
Cable types: NYM, CYKYL, H05VV-F
NYM and CYKYL are cables with solid (rigid) cores in double insulation for fixed wiring: under plaster, in conduit, in trunking, in screed. They hold their shape in boxes and clamp easily in terminals. The CYKYL in the range is made by Unal.
H05VV-F is a flexible cable with stranded cores in a PVC sheath. It is for connecting portable appliances, extension leads, pendant lights, wiring inside boards and temporary lines. It is not buried in walls: stranded cores in screw terminals loosen over time unless crimped with ferrules.
Round or flat
Flat cable is convenient to lay in a narrow chase under plaster and clip to the wall, as it takes less room. Round cable (NYM) has a filler between the cores, passes better through glands, board entries and conduit, and is easier to seal into an outdoor box. Under plaster in a flat the flat type is more common; for conduit and surface runs the round one.
Chase, conduit or trunking
In a chase under plaster the cable is fully hidden, the option for a full renovation. In corrugated conduit the cable runs above a plasterboard ceiling and in the screed, and can be replaced later without opening the finish. Trunking is laid on the wall surface: the choice for a renovation without chasing, offices, garages and adding a socket in a finished room.
Trunking size is chosen so the cables fill about half of it: 16×16 mm for one or two lighting cables, 25×16 for a couple of socket lines, 40×25 and up for main runs with low-voltage cables alongside. Junction boxes go in accessible places and joints are made with terminals, not twisted wires.
How much cable to buy
A simple estimate: from the board to each socket group measure the route along walls and ceiling (not in a straight line), add 0.3–0.5 m per socket and box for connections and a 10–15 % reserve. A typical flat most often takes a 100 m coil of 3×2.5 for sockets and a coil of 3×1.5 for lighting; the kitchen and bathroom are counted separately. Unal power cables, conduit, trunking, boxes and breakers for every cross-section are at ASB Trade, and a manager will help check the list.
Frequently asked questions
Can the whole flat be wired in 2.5 mm²?
Yes: 2.5 instead of 1.5 on lighting is just a reserve. But 2.5 mm² behind a 16 A breaker is not suitable for a hob or other loads above 3.5 kW; those need 4 or 6 mm².
Is H05VV-F suitable for wiring inside walls?
No, it is a flexible cable for portable appliances and extension leads. Fixed wiring uses NYM or CYKYL with solid cores.
What trunking size for two socket lines?
Usually 25×16 mm: two 3×2.5 cables take about half of its cross-section, leaving room to add one more line.