CBS & Emergency Lighting
Follow the power. Size the backup. Test the complete system.
01 · Follow the power
Do not confuse central input failure with local circuit failure
A building can retain power at the CBS while a local normal-lighting circuit loses supply. The approved sensing and control arrangement must still initiate the required emergency operation in that area.
02 · System types & equipment
Central battery system
A common battery bank supplies compatible emergency loads through monitored circuits. Confirm the actual output voltage, AC/DC compatibility, driver characteristics and circuit-control arrangement.
Inspect the charger, battery isolation, protection, battery cabinet, outgoing modules and monitoring controller. A general-purpose UPS is not automatically an approved substitute.
Monitored self-contained system
Each fitting has its own battery and charger. A monitoring network reports tests and faults. Loss of communication must be assessed separately from loss of emergency illumination.
Check permanent supply, local failure sensing, addressing, battery replacement access and reporting.
Maintained / non-maintained
Maintained: the designated light operates during normal conditions and continues in emergency mode.
Non-maintained: the designated emergency lamp normally stays off and illuminates when the relevant normal supply fails.
Exit-sign operation and switched-maintained arrangements follow the approved design.
Installation walk-through
Check access, environmental limits, cabinet clearances, battery support and ventilation against the selected equipment. Verify circuit identification, segregation, cable support, fire performance where specified and compatible terminations.
Record battery type, date, block identification, torque requirements, monitoring address and circuit assignment.
Reference basis
These are subject references, not an automatic compliance verdict. Confirm adopted editions and amendments.
- BS EN 50171: central safety power supply systems.
- IEC 62034: automatic testing of battery-powered emergency lighting.
- Emergency illumination and system application: adopted EN 1838, EN 50172 / BS 5266-1, or AS/NZS 2293 as applicable.
- UAE: approved fire strategy, applicable UAE Fire and Life Safety Code and relevant Civil Defence requirements.
03 · Build the emergency load
Use emergency-mode input watts from the selected driver, not normal-mode wattage or light output in lumens.
| Area / circuit | Quantity | Emergency W each | Total W |
|---|
Allowance is an explicit project choice. It is not a universal standard requirement. AC-output drivers may have different power factors and starting characteristics.
04 · Battery & charger sizing
Energy-based preliminary screen
Charger recovery screen
This is a charge-balance estimate. Confirm battery charging limits, charging profile, selected charger output and the project recharge requirement. Standing load must be entered as battery-side DC watts.
05 · Circuit loading & voltage drop
Single-phase AC or two-wire DC. Choose end load, uniform load or individual points below. AC resistance-only approximation excludes reactance and nonlinear driver behaviour. Constant-power loads use source-voltage current estimates; iterate with manufacturer data where drops are significant.
Use the lowest relevant source voltage when checking emergency operation. Confirm ampacity, protection, disconnection, fault withstand, approved cable fire performance and the actual driver input range separately.
06 · Escape-route layout trainer
Teaching model: every fitting has the same entered candela at every angle, no reflections or obstructions. This is not an IES/LDT photometric calculation. The reported minimum is only across a sampled three-line grid, not a proven minimum throughout the route.
Position fittings for exits, stairs, changes of direction or level, and other required locations. A passing sampled result here does not certify a layout. Use selected luminaire photometry and the adopted criteria for final design.
07 · Fault detective
Quick knowledge check
08 · Submittal & installation review
Record evidence before selecting Verified. This checklist records your review, not certification by the lab.
| Review item | Status | Document / page reference | Engineer’s comment |
|---|
Comments requiring follow-up
09 · Testing & commissioning records
The duration and lux defaults are examples. Replace them with the approved criteria. Do not carry out live discharge or fault tests without an authorised procedure and arrangements to maintain life-safety coverage.
Autonomy readings
| Elapsed min | System V | Battery current A | Battery temp °C | Lowest lux | Alarm / observation |
|---|
Witnessing and handover
10 · Formulas & worked example
Load and battery
P = Σ(quantity × emergency watts) × (1 + spare/100) + auxiliary watts.
Energy = P × autonomy hours. Battery-side power = P / conversion efficiency.
Estimated nominal Ah = P × hours × ageing factor / (battery voltage × efficiency × usable discharge fraction × temperature capacity factor).
Example: 500 W for 3 h, 24 V, efficiency 0.85, usable fraction 0.8, ageing 1.25 and temperature factor 1.0 gives approximately 114.89 Ah. This is an energy estimate, not a manufacturer-approved battery selection.
Charger
Recovery current = selected Ah × fraction to restore / (recharge hours × charge efficiency). Add standing DC load / battery voltage.
Two-wire circuit
Copper resistivity at temperature T: ρ = 0.0175 × [1 + 0.00393 × (T − 20)] Ω·mm²/m.
DC current = watts / volts. AC current = watts / (volts × power factor).
Loop resistance = 2 × one-way length × ρ / conductor area. DC drop = current × loop resistance. Approximate AC resistive drop = current × loop resistance × power factor.
For 100 W, 24 V DC, 50 m one-way and 2.5 mm² copper at 20°C: current 4.167 A, loop resistance 0.7 Ω and drop 2.917 V (12.15%).
Layout teaching model
At a floor sample: E = Σ[I × h / (h² + horizontal-distance²)^(3/2)] × maintenance factor. I is the assumed angular intensity in candela; h is mounting height above the floor.
Real intensity varies with direction and the selected fitting. Spacing, obstructions, uniformity, response time, signs and all adopted requirements need separate verification.
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11 · Fault protection & discrimination
A current-limited inverter may shut down before a conventional breaker clears. Check battery mode and normal/bypass mode separately.
Time comparison at one entered current is a screening check only. It does not establish selectivity over the complete fault range. Check current-limiting behaviour, I²t, breaking capacity, cable thermal withstand, earth faults and tested manufacturer combinations separately.