Emergency Lighting Panel Design: DALI-2 Bus, CPS and Battery Circuits
Emergency lighting panel design must keep emergency circuits operational when the main distribution fails — requiring careful physical and electrical separation from normal lighting circuits, correctly sized backup power for the DALI controller, and commissioning that verifies every aspect of autonomous operation.
The key principle: energised at all times
The fundamental requirement for an emergency lighting distribution circuit is that it must remain energised during normal building operation AND must continue to energise the luminaire charging circuits after a main distribution fault. This single constraint drives every panel design decision that follows.
What "dedicated emergency circuit" actually means
The emergency luminaire must receive mains power continuously — not only during emergencies, but at all times during normal building operation — so that its internal battery charger can maintain the battery at full charge. A luminaire whose mains supply is interrupted by a timed schedule or occupancy sensor will find its battery partially discharged when a real emergency occurs. The dedicated emergency MCB must never be connected to a switched circuit or contactored load. It feeds directly from the incomer, before any building automation switching.
Central Power Supply vs self-contained battery
There are two fundamentally different battery architectures for emergency lighting. The choice is made at design stage and determines the entire panel topology, wiring scheme, and maintenance model.
Central Power Supply (CPS) — IEC 62386 Part 203
One central battery bank (typically 24V DC, rated for the total emergency load of all luminaires) is housed in the main distribution panel or a dedicated CPS cabinet. During a mains failure, the CPS switches all emergency luminaires to 24V DC battery feed via a dedicated low-voltage distribution circuit.
Advantages
- - Single battery to maintain and replace
- - Battery health monitoring centralised
- - Simpler DALI controller configuration
- - Well suited to very large installations (500+ luminaires)
Disadvantages
- - Complex 24V DC cabling to every luminaire
- - Cable cross-section must account for voltage drop over distance
- - CPS cabinet occupies significant panel space
- - Entire system fails if single CPS unit fails
Self-contained battery — IEC 62386 Part 202
Each luminaire contains its own NiMH or Li-ion battery inside the ECG. The 230V mains circuit feeds the luminaires normally — the ECG uses this to charge the battery continuously. On mains failure, the ECG switches to its internal battery and illuminates at rated emergency output autonomously. DALI-2 manages all ECGs for test scheduling and fault monitoring.
Advantages
- - Standard 230V cabling to each luminaire (same as normal lighting)
- - Fault tolerant — one battery failure affects one luminaire only
- - No CPS cabinet required
- - DALI-2 controller manages all batteries remotely via Part 202 queries
Disadvantages
- - Battery replacement requires access to each luminaire
- - Battery cost multiplied by luminaire count
- - Mixed battery ages across installation
Self-contained Part 202 ECGs are the standard choice for modern commercial and residential projects — easier wiring, better fault tolerance, and full DALI-2 remote management. CPS (Part 203) is used primarily in very large commercial buildings with 500+ luminaires where centralised battery maintenance is preferable.
Panel wiring layout — emergency circuit separation
IEC 60364-5-56 (Safety services) requires that emergency circuits are physically separated from normal circuits in the distribution board. This means separate cable raceways in the panel, separate terminal blocks, and clear labelling — not simply a different MCB on the same rail.
Panel layout — emergency circuit zone (text diagram)
┌─────────────────────────────────────────────────────────────┐ │ MAIN DISTRIBUTION BOARD │ │ │ │ ┌─────────────────────────┐ ┌─────────────────────────┐ │ │ │ NORMAL LIGHTING ZONE │ │ EMERGENCY ZONE [RED] │ │ │ │ │ │ │ │ │ │ MCB L1 — Floor 1 │ │ MCB E1 — Escape Fl.1 │ │ │ │ MCB L2 — Floor 2 │ │ MCB E2 — Escape Fl.2 │ │ │ │ MCB L3 — Floor 3 │ │ MCB E3 — Stairwell │ │ │ │ DALI Bus (normal) │ │ MCB E4 — Controller │ │ │ │ Helvar Router (std) │ │ UPS → DALI Controller │ │ │ │ │ │ Helvar Router 950 │ │ │ │ │ │ DALI Bus (emergency) │ │ │ └─────────────────────────┘ └─────────────────────────┘ │ │ │ │ Separate cable raceways — NO shared conduit │ │ Separate neutral terminal blocks per zone │ │ Emergency zone labelled RED: "EMERGENCY — DO NOT SWITCH" │ └─────────────────────────────────────────────────────────────┘
Separate MCB for every emergency circuit
Each emergency circuit gets its own MCB — not shared with any normal lighting circuit. MCB type: C6 or C10 depending on luminaire count. MCBs must be clearly labelled with red markers and 'EMERGENCY CIRCUIT — DO NOT SWITCH' labels. In some jurisdictions (DE, AT) MCBs must be padlocked or covered to prevent accidental isolation.
Physical separation of cable raceways
Emergency circuit cables must run in dedicated conduit or cable trunking, physically separate from normal circuit cables. Where separation is impractical (e.g. rising main shaft), emergency cables must be in a separate conduit within the same shaft. The separation prevents simultaneous damage to both normal and emergency circuits from a single mechanical fault.
Separate neutral terminal blocks
Emergency circuit neutrals must terminate on dedicated neutral terminal blocks, clearly labelled and physically separated from normal circuit neutral blocks. Shared neutrals are prohibited — a fault current on a normal circuit neutral could affect emergency circuit operation.
Dedicated PE conductor
Emergency luminaires require their own protective earth conductors back to the earth bar. The earth bar is shared (one main earth bar per distribution board), but the PE conductors from emergency luminaires must not share a conduit with normal circuit conductors.
Red labelling and documentation
Emergency circuit MCBs, terminal blocks, and cable ends must be labelled red. The distribution board legend must clearly identify all emergency circuits. Panel documentation (as-built diagram) must show the physical layout of the emergency zone and be retained for the life of the building.
3-hour battery requirement
EN 50172 requires that emergency luminaires operate at their rated emergency output for a minimum of 3 hours (180 minutes). This duration is verified by the DALI-2 Part 202 annual duration test. The 3-hour requirement applies to the battery within each luminaire ECG — the luminaire must sustain 100% rated emergency lumen output throughout this period.
| Battery technology | Typical service life | Replacement trigger | Charge time after ADT | Notes |
|---|---|---|---|---|
| NiMH (Nickel Metal Hydride) | 4–6 years | ADT result < 162 min (90% of 180 min rated) | 18–24 hours | Most common in budget-to-mid ECGs. More temperature-sensitive — avoid unventilated areas > 40°C. |
| Li-ion (Lithium-ion) | 8–10 years | ADT result < 162 min or capacity < 80% rated | 6–12 hours | Premium ECGs (Tridonic, Osram DALI-2 EM). Better cycle life and faster recharge. Slightly higher ECG cost. |
| LiFePO4 (Lithium Iron Phosphate) | 10–15 years | ADT result < 162 min | 8–14 hours | Emerging in high-specification ECGs. Safest lithium chemistry. Best for sealed luminaires in difficult-access areas. |
DALI controller backup power — UPS specification
The Helvar Router 950 or Tridonic DALI-2 controller must remain powered during a mains failure. Without power, it cannot continue test logging, cannot receive the battery fault events generated when individual ECGs detect problems during an actual emergency, and cannot communicate via KNX to trigger building management alerts.
Recommended UPS specification for DALI controller
Note that UPS backup of the DALI controller does not substitute for the self-contained battery in each luminaire. Even without the controller, Part 202 ECGs illuminate autonomously on mains failure. The UPS enables the controller to continue its monitoring and logging function — required for full EN 50172 audit trail — during the mains failure event.
Inhibit time windows — EN 50172 Section 4.3.2
The DALI-2 inhibit command suppresses pending tests during occupied hours. This prevents non-maintained luminaires from briefly illuminating (and startling occupants) when a scheduled test triggers during the working day. However, EN 50172 Section 4.3.2 imposes a strict maximum: inhibit must not be maintained for more than 24 consecutive hours.
Hotel configuration
Send Inhibit every 14 minutes from 08:00 to 22:00 (14 hours per day). Non-inhabited period 22:00–08:00 allows 8 hours of test window. Monthly test scheduled for 03:00 in the available window. Inhibit duration: 14 hours continuous — well within the 24-hour limit.
Office configuration
Send Inhibit from 07:00 to 19:00 (12 hours per day). Test window 19:00–07:00. Monthly test at 02:00. Annual duration test requires the building to be unoccupied for at least 3 hours plus recharging buffer — August weeknight at 01:00 is the standard slot for office buildings.
24-hour limit enforcement
If the controller fails to end inhibit (e.g. controller software bug or network fault), the ECG's internal 24-hour inhibit timer expires automatically and the ECG schedules its own test at the next available opportunity. This autonomous override is a Part 202 requirement — the ECG must not allow indefinite test suppression regardless of controller state.
Commissioning requirement
The inhibit schedule must be configured before building handover and verified during commissioning: check that the Inhibit command appears on the DALI bus analyser during business hours, and that no Inhibit is sent during the scheduled test window. Helvar Designer shows the configured inhibit schedule in the emergency controller properties panel.
Commissioning checklist
Emergency lighting commissioning must be documented and retained as part of the building handover package. The following 7-step sequence covers the minimum required verification for a DALI-2 Part 202 installation.
Emergency DALI-2 commissioning — 7-step checklist
1. DALI COMMISSION Run DALI scan on emergency segment via Helvar Designer. Verify all expected ECG devices are detected (count must match the emergency luminaire schedule from design). Confirm no unaddressed ECGs remain (short address = 255). 2. SET SHORT ADDRESSES Assign sequential short addresses (0–63) to each ECG. Document the address-to-luminaire mapping in the as-built schedule: Address 00 = Floor 1 Stairwell North, etc. This mapping is essential for fault location during operation. 3. CONFIGURE EMERGENCY PROFILE For each ECG: set emergency mode (non-maintained/maintained), set emergency level (100% rated output — do not reduce), set rest mode level (1% after duration test), set rated duration (180 minutes for EN 50172 3-hour requirement). 4. SET TEST SCHEDULE Configure monthly function test: first Sunday, 03:00. Configure annual duration test: August, first weeknight, 01:00. Configure inhibit schedule: business hours as agreed with client. Verify inhibit period does not exceed 24 consecutive hours. 5. PERFORM MANUAL FUNCTION TEST Send Start Function Test to all ECGs. Verify all ECGs run on battery and return PASS result. Check Router 950 database for logged results — confirm timestamp, pass/fail, and measured duration for each ECG. Address any FAIL results before sign-off. 6. VERIFY LOG OUTPUT Generate PDF report from Router 950 / Helvar Designer. Confirm report includes: building address, installation date, all ECG addresses, test type, test date, result, duration. Confirm report format is acceptable to client's insurer/fire authority. Export report and include in building handover documentation. 7. CHECK INHIBIT TIME WINDOWS Connect DALI bus analyser (e.g. Lunatone DALI Cockpit USB) to emergency segment. Verify Inhibit command is transmitted during configured business hours at ≤14-minute intervals. Verify NO Inhibit is transmitted during the scheduled test window. Verify ECG autonomous test override: disconnect controller power for 25 hours → ECG should self-test and store result independently.
Emergency lighting in your panel
PanelCraft designs panels with dedicated DALI-2 emergency circuits, physically separated from standard lighting, pre-commissioned and tested before delivery — with EN 50172 documentation package included.
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