Reference
UK lighting wiring diagrams
The common ways to wire domestic lighting in the UK — one, two and three switches (intermediate), and how the same switching controls one, two or three lights. Diagrams show the switch-drop / loop-in-at-ceiling method used in most UK installations to BS 7671.
Reference only
These diagrams are simplified for teaching. Actual installations must be designed and installed by a competent person to BS 7671:2018+A3:2024/A4:2026. Switch-drops using twin-and-earth cable require a brown line, a brown switched-line (blue sleeved brown) and an earth — with the neutral looped at the ceiling rose.
Legend
- Brown — Line (permanent L)
- Blue — Neutral (N)
- Switched line (blue sleeved brown in T&E)
- Green/Yellow — CPC (earth)
- Strapper (between switches)
- Grey sheath — T&E cable (2C+E)
In the topology diagrams below, earth (CPC) is present at every point but drawn only where it clarifies the wiring. In the T&E diagrams further down, the CPC is drawn explicitly.
One light, one switch — one-way switching
The simplest arrangement. Line goes to the switch, switched line goes to the lamp, neutral goes directly to the lamp. This is what a hallway or WC light typically uses.
One-way switch → one lamp
Line to switch COM; switched-line back to lamp; neutral straight to lamp.
One light, two switches — two-way switching
Two switches control the same lamp — either can turn it on or off. Standard for stairs (top and bottom of stairs) and long hallways with a door at each end. Uses 3-core-and-earth "strappers" between the switches.
Two-way switching (2 switches, 1 lamp)
Line to COM of S1; L1/L2 of S1 to L1/L2 of S2 (strappers); COM of S2 back to lamp; neutral straight to lamp.
See it working — tap the switches
The same two-way circuit as a working demo, wired the way it is most often done in practice: feed to the rose on the loop, one T&E drop to switch 1, and 3-core-and-earth between the switches. The permanent line runs down to L1 of switch 1 and the switch wire returns from L2 — the usual conversion method, which reuses an existing one-way drop without disturbing the rose (Diagram C below shows the alternative, with the feed on COM of switch 1). Notice the brown cores are live whenever the circuit is energised, no matter which way the switches sit — worth remembering before opening a switch box. The black and grey strappers, and the blue switch wire in the drop, are sleeved brown at both ends because they are line conductors, not neutrals (Regulation 514.4).
Lamp on — power flows: supply → L1 of switch 1 → common → brown strapper → common of switch 2 → L2 → grey strapper → L2 of switch 1 → up the switch drop to the lamp.
One light, three (or more) switches — intermediate switching
Every switch beyond the second is an intermediate switch, wired between the two two-way end switches. It crosses over the two strappers. You can add as many intermediate switches as you like in the middle of the run — common on long landings or open-plan spaces with three or four entrances.
Intermediate switching (3 switches, 1 lamp)
Two-way at each end, intermediate switch in the middle crosses the strappers.
See intermediate switching working — tap the switches
The three-switch circuit as a working demo: feed to the rose on the loop, a T&E drop to switch 1, then 3-core-and-earth from switch 1 to the intermediate and on to switch 2. The intermediate is a four-terminal crossover — straight through in one position, crossed over in the other — and only the two pairs of strappers (and the CPC) connect to it; the brown cores are jointed through its back box. Flip any one of the three switches and the lamp changes state, wherever the other two are set. The strappers are sleeved brown at both ends because they are line conductors (Regulation 514.4).
Lamp on — supply → common of switch 1 (via L1) → brown strappers → common of switch 2 → L2 → grey strapper → straight through the intermediate → L2 of switch 1 → up the switch drop to the lamp.
Two lamps, one switch
Two lamps wired in parallel from the same switched line — e.g. two pendants over a dining table, or two downlighters over a kitchen island. Lamps are always wired in parallel in domestic lighting; never in series (series would leave both dim and both fail if either goes).
One switch → two lamps in parallel
Switched line feeds both lamps; both share the neutral.
Three lamps, one switch
Same principle — three lamps in parallel on a single switch. Typical for a set of three downlighters over a worktop, or three pendants over a breakfast bar.
One switch → three lamps in parallel
Switched line loops from lamp to lamp; each lamp also connects to the neutral.
Two lamps, two-way switching
Combine the two ideas: two switches controlling two lamps together. Both lamps come on and off from either switch. Add an intermediate in the middle for a third switch.
Two-way switching → two lamps
Standard 2-way pair, then the COM of S2 feeds both lamps in parallel.
Cable level
The same circuits in real twin-and-earth (T&E) cable
The diagrams above show topology. In practice UK lighting is wired in twin-and-earth (brown / blue / bare CPC) plus, where two-way or intermediate switching is used, 3-core-and-earth(brown / black / grey / bare CPC) between the switches. The lampholder is fed from a 3-plate loop-in ceiling rose — three separate terminal blocks: Loop (permanent line), Neutral, and Switched line, with a dedicated earth (CPC) bar.
The blue conductor of a T&E switch drop is always sleeved brown at both ends because it is a switched line, not a neutral (Regulation 514.4). In the diagrams below it is shown dashed amber for clarity.
A. One-way switching — 3-plate loop-in rose
Feed from the consumer unit lands on the Loop, Neutral and earth terminals of the rose. A single T&E drops down to the switch: brown = permanent line to COM; blue (sleeved brown) = switched line back up to the SwL block. The lampholder is fed from SwL (line) and N.
One-way switching in T&E (single lamp)
Feed at ceiling; one T&E drop to a one-way switch.
B. Two lamps looped rose-to-rose (still one switch)
The permanent line, neutral and switched line are looped from the first rose to the second in a further T&E — but this one is a 3-core loop (perm L on LOOP-to-LOOP, N-to-N, SwL-to-SwL, CPC). Since a standard T&E only has two conductors, the loop between roses is normally run in 3-core-and-earth so all three functions travel together.
Loop-in: two lamps, one switch
Feed → rose 1 → 3C+E loop → rose 2. Switch drop from rose 1 only.
C. Two-way switching — feed at rose, 3C+E strappers
The switch drop is one T&E from the rose to S1 (brown = perm line to S1 COM, blue-sleeved-brown = SwL return to the rose SwL block). Between S1 and S2 is 3-core-and-earth: brown and black are the two strappers landed on L1 and L2, grey (sleeved brown) carries the SwL from S2's COM back through the S1 back-box and up the T&E's blue core to the rose. Either switch turns the lamp on or off.
Two-way switching in T&E + 3C+E
One T&E drop to S1 (perm L down, SwL up). 3C+E between S1 and S2.
D. Intermediate switching — 3 switches in T&E / 3C+E
Same T&E switch drop from the rose to S1. Between S1 and S2, and again between S2 and S3, is 3-core-and-earth. The intermediate switch (S2) has four terminals and swaps the two strappers when it operates; the grey conductor (sleeved brown) again carries the SwL return from S3's COM back to the rose. Any number of intermediate switches can be added by repeating S2.
Intermediate switching in T&E + 3C+E
Rose → S1 (T&E drop) → S2 (intermediate, 3C+E each side) → S3.
Inside an intermediate switch
An intermediate switch is a 4-terminal, double-pole crossover. It has no COM. The four terminals are usually marked L1 / L2 (top) and L3 / L4 (bottom), or simply 1 · 2 · 3 · 4. Internally it does one of two things depending on switch position:
- • Position A (straight-through): 1↔3 and 2↔4 — the two strappers pass through unchanged.
- • Position B (crossed): 1↔4 and 2↔3 — the strappers swap over.
That crossover is the whole trick: flipping any intermediate reverses which strapper is "live", which flips the state of the lamp regardless of where S1 and S3 are set. You can chain as many intermediates as you like between the two end two-way switches.
Terminal-by-terminal in T&E / 3C+E
Using the diagram above (Rose → S1 → S2 intermediate → S3), with strappers sleeved brown at both ends:
- 3C+E from S1 → S2 (left side):
- – Brown (S1 L1) → S2 terminal 1 (top-left).
- – Black sleeved brown (S1 L2) → S2 terminal 2 (top-right).
- – Grey sleeved brown (S1 COM = permanent live from the switch drop) is not used at S2 — cap it off in the back-box, or better, don't bring it through: the permanent live only needs to reach S1's COM.
- – CPC → earth terminal in the S2 back-box (and to the metal plate if used).
- 3C+E from S2 → S3 (right side):
- – Brown → S2 terminal 3 (bottom-left) and S3 L1.
- – Black sleeved brown → S2 terminal 4 (bottom-right) and S3 L2.
- – Grey sleeved brown → S3 COM. This is the switched-live return that goes all the way back through S1's drop, up the T&E to the rose's SwL terminal, and feeds the lampholder.
- – CPC → earth terminal at both ends.
- Result at S2: only terminals 1–2–3–4 are used. Position A holds 1-3 / 2-4 straight; position B swaps to 1-4 / 2-3. Nothing else is wired to the intermediate — no permanent live, no neutral, only the two pairs of strappers and the CPC.
Truth table — S1 / S2 (intermediate) / S3
Any single switch flip changes the lamp state. With three switches there are 8 combinations — 4 ON and 4 OFF.
| S1 | S2 (int.) | S3 | Lamp |
|---|---|---|---|
| L1 | Straight | L1 | ON |
| L1 | Straight | L2 | OFF |
| L1 | Crossed | L1 | OFF |
| L1 | Crossed | L2 | ON |
| L2 | Straight | L1 | OFF |
| L2 | Straight | L2 | ON |
| L2 | Crossed | L1 | ON |
| L2 | Crossed | L2 | OFF |
Reading a 3-plate ceiling rose in real life
- • Loop terminal — all the permanent (unswitched) brown lines land here. This is where the perm-L feeds out to switch drops or to the next rose. Nothing on the lampholder connects to this block.
- • Neutral terminal — all blue neutrals land here, including the lampholder neutral flex.
- • Switched-live terminal — the sleeved-brown return from the switch(es) lands here and also feeds the lampholder line flex.
- • Earth bar — every CPC (bare copper, sleeved green/yellow) from every cable lands on the rose earth terminal, including a CPC to any metal lampshade or backplate (411.3.1.1).
- • A modern rose has slots for two or three cables — an incoming feed T&E, an outgoing 3C+E loop to the next rose, and a T&E switch drop.
Notes for anyone wiring this in practice
- • Where the blue core of a twin-and-earth switch drop carries the switched line, sleeve it brown (or mark it with brown tape) at both ends so nobody mistakes it for a neutral. Modern colours: brown = line, blue = neutral, green/yellow = CPC.
- • Two-way switch drops need 3-core-and-earth (brown, black, grey + CPC) between switches. Black and grey are re-purposed as strappers and should be sleeved brown at both ends.
- • Every switch back-box and every ceiling rose must have a CPC terminated at an earth terminal — including metal switch plates (Regulation 411.3.1.1).
- • Domestic lighting circuits in the UK are typically 6A radials from a 6A MCB/RCBO in the consumer unit; some installers use 10A. Number of points is limited by the circuit design, not a fixed maximum.
- • All lighting circuits in a domestic property require RCD protection (30 mA) — normally an RCBO on the lighting circuit at the consumer unit.
Need a lighting circuit designed or added?
Paul designs and installs new lighting circuits, converts one-way switching to two-way or intermediate, and adds dimmer, smart or KNX control across Brighton, Hove, Sussex, Kent and London.