How to Wire Emergency Lights: Complete Guide

Emergency lighting only has one job: keep escape routes visible when the normal mains supply fails. That single job hides a fair amount of wiring detail -- whether a fitting needs two circuits or three, whether it uses battery backup at all, and how you test it without shutting down the building's lighting. Get the wiring wrong and you end up with a fitting that looks fine on the wall but does nothing during a real power cut, which defeats the point of installing it.

This guide covers the fitting types, wiring for maintained and non-maintained emergency lights, key-switch test circuits, central battery versus self-contained systems, and the basics of BS 5266 (UK) and NFPA 101 / NEC Article 700 (US). It also includes a full step-by-step wiring procedure, a wire and terminal reference table, and a troubleshooting table for the most common faults you will encounter after installation.

Maintained, Non-Maintained, and Sustained Fittings

Not all emergency lights work the same way, and the wiring depends entirely on which type you are installing.

Non-maintained fittings stay off during normal operation. The lamp only switches on when it detects a loss of the mains supply, drawing on its internal battery. These are the most common type for open-area and escape-route lighting -- corridors, stairwells, and fire exit routes where you only need the fitting lit during a power failure.

Maintained fittings run their lamp continuously, whether mains power is present or not. Under normal conditions the lamp draws from the mains supply; if the mains fails, the same lamp switches over to battery power without going dark. Maintained fittings are the standard choice for illuminated exit signs, because a sign that says "EXIT" is only useful if people can see it at all times, not just during an outage.

Sustained fittings combine both behaviors in one unit, typically housing two lamps (or a lamp with two circuits) -- one that runs continuously off the mains like a maintained fitting, and a second emergency circuit that only activates on mains failure. These suit a fitting that needs to double as general/sign lighting and dedicated emergency lighting.

Knowing which type you are wiring determines how many conductors run to the fitting, which is the main wiring difference covered below.

How Emergency Lighting Circuits Work

Every self-contained emergency light contains three core components: a rechargeable battery, a charging circuit, and a sensing circuit that detects loss of supply. Under normal conditions, mains power keeps the battery topped up and (for maintained fittings) powers the lamp directly. The moment the sensing circuit detects the permanent live has dropped, it switches the lamp to battery power fast enough that there is no perceptible gap in illumination.

This is why the "permanent live" feed matters: it has to come from a source that stays live even when the general lighting circuit for that area is switched off, otherwise the battery never recharges and the fitting will not perform when you need it. The permanent live is usually taken from an unswitched fused spur or a dedicated lighting circuit not controlled by the room's ordinary wall switches.

Codes and Standards: BS 5266 and NFPA 101 / NEC 700

BS 5266 is the UK code of practice for emergency lighting design, installation, and maintenance. It sets out duration ratings for how long a fitting must operate on battery power after a mains failure -- commonly either 1 hour or 3 hours, depending on the building's evacuation strategy. A 1-hour rating generally suits a building that evacuates quickly and is then re-occupied. A 3-hour rating is more common overall and is typically specified where the building may not be immediately re-entered, such as places of assembly, so the lighting needs to keep working longer. BS 5266 also sets minimum illuminance levels along designated escape routes, though the exact lux values and testing intervals depend on the specific space and should be confirmed against the current version of the standard rather than assumed. Periodic testing, including monthly function tests and an annual full-duration discharge test, is generally addressed under BS 5266-8 and the related EN 50172 standard, which is why key-switch test facilities (covered below) exist in the first place.

NFPA 101 (the Life Safety Code) and NEC Article 700 are the equivalent US references. NFPA 101 sets performance requirements for emergency illumination along means of egress, including a commonly cited minimum duration of around 1.5 hours and minimum illumination levels along the escape path. NEC Article 700 covers the wiring side: emergency circuits must be kept independent of other, non-emergency wiring, protected from damage that could disable both the normal and emergency source at once, and supplied through equipment intended for emergency use -- in practice, emergency lighting belongs on its own dedicated, protected circuit rather than sharing with everyday lighting or receptacles. Treat these figures as a starting point for research, not a substitute for checking the current adopted edition of the code in your jurisdiction.

Central Battery Systems vs Self-Contained Fittings

There are two different ways to supply battery backup, and the choice affects the wiring at every fitting.

Self-contained fittings have their own battery and charging circuit built into the luminaire. Each fitting operates independently -- if one fitting's battery fails, only that fitting is affected. This is the simpler, more common approach for small to mid-size premises, since each fitting just needs a permanent live (and a switched live, for maintained types) run to it like any other lighting point.

Central battery systems use one large battery and charger, usually housed in a plant room, feeding multiple luminaires throughout the building over fire-rated cable. There is no battery inside each fitting -- the fittings are effectively just lamps fed from the central unit. Central systems suit larger buildings because they centralize monitoring and maintenance (one battery bank to test instead of dozens scattered through the building), but the distribution cable itself must be fire-rated and correctly segregated, since a single cable fault can take out emergency lighting across a wide area. These are specialist installations that typically need coordination with a fire alarm or emergency lighting designer rather than being wired as a simple lighting circuit.

This guide focuses on self-contained fittings, since that is what most electricians and maintenance staff encounter when wiring an individual emergency light.

Tools and Materials Needed

Tools

• Non-contact voltage tester
• Flathead and Phillips screwdrivers
• Wire strippers
• Cable cutters
• Ladder or step stool rated for the working height
• Torch or headlamp (useful given you may be testing with the lights off)

Materials

• Emergency light fitting (maintained, non-maintained, or sustained, matched to the application)
• 3-core-and-earth cable (for maintained fittings) or 2-core-and-earth cable (for non-maintained fittings)
• Key-operated test switch, if the fitting does not have a built-in test facility
• Wire connectors or a terminal block
• Cable clips and fixings appropriate to the ceiling or wall construction
• Fused spur or dedicated breaker for the permanent live feed

Wire and Terminal Reference

"3-core-and-earth" in UK terminology means three insulated conductors plus a separate earth -- four conductors total. Non-maintained fittings generally only need 2-core-and-earth, since there is no switched live to carry.

Always check the specific terminal labeling on the fitting -- manufacturers do not use identical markings, and the fitting's own wiring diagram takes priority over generic color conventions if the two conflict.

Step-by-Step Wiring Instructions

Wiring a Maintained Fitting

1. Isolate the supply. Turn off the breaker feeding the circuit you are working on, and separately confirm the permanent live feed (which may come from a different, always-on circuit) is also isolated.
2. Verify the circuit is dead with a non-contact voltage tester, then a second confirmed-working tester or multimeter, at the fitting location.
3. Mount the fitting to the ceiling or wall per the manufacturer's fixing instructions, ensuring it is secure before wiring it live.
4. Run the permanent live from the unswitched fused spur or dedicated always-on circuit to the fitting's permanent live terminal.
5. Run the switched live from the local lighting circuit's switch leg to the fitting's switched live terminal, so the lamp follows the room's normal light switch during regular operation.
6. Connect the neutral conductor to the fitting's neutral terminal, and confirm it traces back to the correct neutral bar for the circuit supplying the permanent live.
7. Connect the earth conductor, sleeved in green/yellow, to the fitting's earth terminal.
8. Wire the key-switch test unit, if fitted separately rather than built into the luminaire, following the manufacturer's diagram -- this typically interrupts the permanent live to simulate a mains failure without touching the switched live.
9. Double-check every terminal is fully seated with no bare conductor exposed outside it.
10. Restore power at the breaker and confirm the lamp is lit (maintained fittings should illuminate immediately).
11. Run a test cycle using the key switch or test button to simulate a mains failure, and confirm the fitting switches to battery power and the lamp stays lit.
12. Reinstate normal operation immediately after testing -- do not leave the fitting isolated or in test mode.

Wiring a Non-Maintained Fitting

The procedure is largely the same, except there is no switched live to run:

1. Isolate and verify the supply is dead, as above.
2. Mount the fitting.
3. Connect the permanent live to the fitting's live terminal -- the only live conductor needed, since the lamp is not controlled by the room's light switch.
4. Connect the neutral and earth as above.
5. Wire the key-switch test facility, if separate from the fitting.
6. Restore power. The lamp should stay off under normal conditions.
7. Test using the key switch and confirm the lamp lights on simulated failure, then goes off again once the failure clears and charging resumes.

Key-Switch Test Circuits

A key-operated test switch lets you simulate a mains failure at a single fitting (or a group on the same test loop) without switching off the building's actual lighting circuit. Turning the key interrupts the permanent live feed to the fitting being tested, triggering the same failure-detection response as a real power cut -- the lamp switches to battery power. Releasing the key restores the permanent live and the fitting reverts to normal charging.

This matters for periodic testing under BS 5266-8 and EN 50172, which call for regular function tests (commonly monthly) and a full-duration discharge test (commonly annual) to confirm the battery still holds enough charge to meet its rated duration. Without a test switch, verifying a fitting's battery performance would mean isolating the whole lighting circuit -- disruptive in an occupied building. Key-switch loops are typically wired so one switch tests several fittings on the same permanent live run, though large installations often stagger test loops so an entire floor is not thrown into test mode at once.

Label any key-switch test facility clearly at the switch location and note which fittings it tests -- an unlabeled test switch is easy to mistake for a normal light switch, and flipping it accidentally discharges the battery unnecessarily and can mask a real fault during the next scheduled test.

Safety Warnings

• Isolate the correct circuit before starting. Emergency lighting is often fed from a separate, always-on circuit from the room's normal lighting -- isolating only the room's light switch will not make the permanent live safe to touch. Identify and isolate both feeds.
• Verify dead with a tester, not by assumption, every time -- even on a circuit you isolated minutes earlier.
• Working at height. Most emergency lighting is ceiling-mounted. Use a ladder or platform rated for the task, especially in stairwells where fittings often sit over a drop.
• Battery handling and disposal. Emergency light batteries are typically sealed lead-acid or NiCd/NiMH types. Do not puncture, short-circuit, or bin them in general waste -- follow local battery-recycling regulations and handle a leaking or swollen battery with care, since the electrolyte can be corrosive.
• Never leave a fitting disabled after testing. Reinstate normal operation before you leave the site -- a fitting left disabled provides no protection during a real emergency and is easy to forget about.
• Central battery systems carry far more stored energy than a self-contained fitting's small internal battery. Treat the battery room and its distribution cabling as a job for someone trained on that specific system.

Common Mistakes and Troubleshooting

The most frequent wiring error is running only a single live conductor to a maintained fitting -- without a dedicated switched live, the lamp cannot follow the room's light switch and stays permanently on or off, depending on how the remaining conductor is wired. The second most common mistake is taking the permanent live from a switched circuit rather than a genuinely unswitched source: the battery stops charging every time someone turns off the room lights, and the fitting quietly loses backup capacity without anyone noticing until a real power failure exposes it.

Key Takeaways

• Non-maintained fittings light up only on mains failure; maintained fittings run continuously and switch to battery on failure; sustained fittings combine both in one unit.
• A key-switch test circuit simulates mains failure at a fitting so you can test the battery and lamp without isolating the whole lighting circuit -- relevant to periodic testing under BS 5266-8 and EN 50172.
• BS 5266 (UK) typically calls for 1-hour or 3-hour duration ratings depending on the evacuation strategy; NFPA 101 and NEC Article 700 (US) generally call for around 1.5 hours minimum duration and a dedicated, protected emergency circuit -- confirm exact figures against the current adopted code.
• Maintained fittings need 3-core-and-earth cable (permanent live, switched live, neutral, earth); non-maintained fittings typically only need 2-core-and-earth (permanent live, neutral, earth).
• Self-contained fittings carry their own battery and charger; central battery systems feed many luminaires from one plant-room battery over fire-rated cable and are a specialist installation.
• Always isolate both the permanent live feed and the local lighting circuit, verify dead, and never leave a fitting disabled after testing.
• The most common wiring fault is taking the permanent live from a switched source instead of a genuinely unswitched one, which silently stops the battery from charging.

Frequently asked questions

What is the difference between maintained and non-maintained emergency lighting?

A maintained fitting keeps its lamp lit all the time, powered by the mains under normal conditions and switching to battery on failure -- typical for exit signs. A non-maintained fitting stays off during normal operation and only lights when it detects a mains failure, which is typical for corridors, stairwells, and open escape routes.

What wires does a maintained emergency light need?

A maintained fitting needs 3-core-and-earth cable: a permanent live to keep the battery charging continuously, a switched live that controls the lamp alongside the room's normal light switch, a neutral, and an earth. Non-maintained fittings typically only need 2-core-and-earth, since there is no switched live to carry.

What does a key-switch test do on an emergency light?

A key-operated test switch interrupts the permanent live to a fitting, simulating a mains failure so you can confirm the battery and lamp work without isolating the entire lighting circuit. This supports periodic testing schedules -- commonly monthly function tests and an annual full-duration discharge test -- required for ongoing emergency lighting compliance.

How long should emergency lights last on battery power?

Under BS 5266 in the UK, fittings are commonly rated for either 1 hour or 3 hours of battery operation, depending on the building's evacuation strategy, with 3 hours being more typical. In the US, NFPA 101 commonly cites a minimum duration of around 1.5 hours. Always confirm exact figures against the current adopted code.

What is a central battery emergency lighting system?

A central battery system uses one large battery and charger, usually in a plant room, to feed multiple emergency luminaires through fire-rated distribution cable, rather than each fitting holding its own battery. It centralizes maintenance and monitoring but is a specialist installation, typically suited to larger buildings rather than small premises.

Why is my emergency light staying on all the time?

This usually means the switched live is missing or has been miswired directly to the permanent live, so the lamp never turns off with the room lights. It can also happen on a non-maintained fitting if the lamp circuit is bridged to the permanent live instead of only energizing on loss of supply. Recheck the switched live connection.

Interactive diagrams for this guide

• Emergency Light Wiring Diagram
• Emergency Light Circuit Diagram
• Emergency Light Diagram
• Rechargeable Emergency Light Circuit Diagram
• 4v Rechargeable Emergency Light Circuit Diagram
• Key Switch Wiring Diagram
• Key Switch Diagram
• 4 Wire Key Switch Diagram

Related guides

• How to Wire Lights in Parallel: Complete Guide
• Two Lights One Switch Wiring Diagram