Safety Services: Sources of Supply and Changeover Time Classification
- MTS DNC ENERGY CONSULTANTS LIMITED
- Jan 1
- 3 min read
Updated: Jan 3
Electrical safety services are designed to ensure that critical systems continue to operate, or are restored within a defined time, following the failure of the normal electrical supply. These services are essential for life safety, fire protection, evacuation, and critical operations.
This article explains the recognised sources of supply for safety services, where each is typically used, their advantages, and how safety supplies are classified based on automation and changeover time.
🔌 Recognised Sources for Safety Services
Standards such as IS 10101 recognise the following sources as acceptable for safety services, provided they meet independence and reliability requirements.
🔋 1. Storage Batteries
Where They Are Used
Storage batteries are widely used where immediate continuity of supply is required:
Emergency lighting
Fire alarm and detection systems
UPS systems for IT and control panels
Security and access control systems
Medical and life-safety equipment
Advantages
No interruption in supply
Instant response (milliseconds)
Independent of mechanical systems
Silent operation
Ideal for bridging generator start-up time
Typical Limitation
Limited autonomy
Requires routine testing and periodic replacement
🔋 2. Primary Cells (Non-Rechargeable Batteries)
Where They Are Used
Primary cells are used for low-power, long-duration safety functions:
Fire alarm backup supplies
Standalone emergency luminaires
Emergency communication systems
Remote sensors and monitoring devices
Advantages
Long shelf life
High reliability for small loads
No charging system required
Simple installation
Typical Limitation
Not suitable for high loads
Must be replaced once discharged
⚙️ 3. Generator Sets Independent of the Normal Supply
Where They Are Used
Generator sets are used to supply medium to high power safety and essential services:
Hospitals and healthcare facilities
High-rise residential buildings
Commercial buildings and offices
Industrial facilities
Firefighting lifts and smoke control systems
Advantages
Capable of supplying large loads
Long operating duration with fuel replenishment
Suitable for prolonged power outages
Can support multiple safety services simultaneously
Typical Limitation
Start-up delay
Requires maintenance, fuel storage, and testing
Mechanical components introduce failure risk
🔌 4. Separate Feeder from the Supply Network (Independent Feeder)
Where They Are Used
A separate feeder is an alternative supply route from the utility network that is effectively independent of the normal feeder:
Hospitals
Transport hubs
Data centres
Large commercial or mixed-use developments
Advantages
No on-site generation required
High reliability if true independence is achieved
Continuous supply during single network faults
Low operational maintenance for the building owner
Typical Limitation
Dependent on utility provider availability
Independence must be demonstrable
Higher connection and standing charges
🔄 Classification of Safety Supplies by Mode of Operation
Safety supplies are classified based on how they are started.
🔹 Non-Automatic Safety Supply
Starting is initiated by an operator
Examples:
Manually started generators
Manual changeover switches
⚠️ These supplies are generally not acceptable for life-safety systems, as they rely on human intervention and introduce delays.
🔹 Automatic Safety Supply
Starting is independent of an operator
Mandatory for life-safety and fire protection systems
Further classified by changeover time
⏱️ Automatic Safety Supply Classification by Changeover Time
Classification | Maximum Changeover Time | Typical Applications |
No break | 0 s | UPS systems, control systems, data centres |
Very short break | ≤ 0.15 s | Emergency lighting (electronic control) |
Short break | ≤ 0.5 s | Fire alarm systems, security systems |
Average break | ≤ 5 s | Smoke extract systems, firefighting lifts |
Medium break | ≤ 15 s | Emergency generators for essential services |
Long break | > 15 s | Non-critical essential loads |
🧠 Key Design Considerations
When designing safety services, engineers must consider:
Acceptable changeover time for each system
Load criticality and classification
Required autonomy duration
Independence from the normal supply
Testing and maintenance requirements
Compliance with IS 10101 and fire safety regulations
In many installations, multiple safety sources are combined, such as batteries providing no-break supply while generators provide long-term backup.
✅ Final Thoughts
Safety services are not optional design features — they are critical systems that protect life and property.
Correct selection of the safety supply source and changeover classification ensures:
Continuous operation of life-safety systems
Regulatory compliance
Reduced operational and legal risk
Improved resilience during power failures
A robust safety services strategy always aligns the source of supply with the required changeover time and the criticality of the load.
📍 Disclaimer
The content shared in these posts is intended for informational purposes only and should not be interpreted as design advice, specifications, or a calculation template. For professional guidance or design services, please contact us through our contact form.
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