Understanding Extra-Low Voltage (ELV) and Low Voltage (LV)
- MTS DNC ENERGY CONSULTANTS LIMITED
- Dec 31, 2025
- 3 min read
Updated: Jan 3
🎛️ In Accordance with IS 10101
IS 10101 is the Irish National Wiring Rules for low-voltage electrical installations.Within this standard, electrical systems are classified into Extra-Low Voltage (ELV) and Low Voltage (LV) based on their nominal voltage levels.
This classification is fundamental to electrical safety, equipment selection, and protective measures.
🎛️ Why Voltage Classification Matters
Under IS 10101, the voltage level determines:
Electric shock risk
Required protective measures
Insulation and clearance requirements
Equipment ratings
Installation and maintenance practices
Correct classification ensures installations are safe, compliant, and fit for purpose.
🎛️ Extra-Low Voltage (ELV)
🔌 Definition (IS 10101)
A system is classified as Extra-Low Voltage (ELV) when both of the following conditions are met:
Nominal voltage to earth ≤ 50 V AC, and
Nominal voltage between live conductors ≤ 50 V AC
If either limit is exceeded, the system is no longer ELV.
🎛️ Types of ELV Systems
Within the ELV voltage range, IS 10101 recognises different protective arrangements:
SELV (Separated Extra-Low Voltage)– Electrically separated from higher-voltage systems– No intentional earth connection
PELV (Protective Extra-Low Voltage)– Similar to SELV– One point may be connected to earth
These are protective measures, not separate voltage bands.
🏗️ Typical ELV Applications
ELV systems are commonly used where enhanced safety is required:
Fire alarm systems
Control and automation circuits
Data and communication systems
Access control and security
Sensors and instrumentation
ELV significantly reduces the risk of electric shock.
🎛️ Low Voltage (LV)
🔌 Definition (IS 10101)
A system is classified as Low Voltage (LV) when:
50 V < nominal voltage to earth ≤ 600 V AC, and
50 V < nominal voltage between live conductors ≤ 1,000 V AC
This voltage band covers the majority of building electrical installations.
1️⃣ Three-Phase Systems Basics
Most commercial and industrial LV systems use three-phase power. A common setup is 400/230 V:
400 V → phase-to-phase voltage (voltage measured between any two of the three live conductors: L1-L2, L2-L3, L3-L1)
230 V → phase-to-neutral (or phase-to-earth) voltage (voltage measured from any live conductor to neutral or earth)
So, in a 400/230 V system:
Vphase−to−phase=400 V
Vphase−to−neutral=230 V
2️⃣ Why They Are Different
The difference is due to the geometry of a three-phase system. For a balanced three-phase system:
This is why phase-to-phase voltage is always higher than phase-to-earth voltage in a three-phase system.
🏗️ Typical LV Applications
LV systems supply:
Residential buildings (230 V)
Commercial buildings (230 / 400 V)
Lighting and socket outlets
HVAC and mechanical systems
General building services
Because LV presents a higher shock risk, protective measures such as earthing, RCDs, and coordinated protective devices are mandatory.
🎛️ Practical Examples (IS 10101 Context)
System | Phase-to-Earth | Phase-to-Phase | Classification |
Control circuit | 24 V | 24 V | ELV |
Access control PSU | 48 V | 48 V | ELV |
Single-phase supply | 230 V | — | LV |
Three-phase supply | 230 V | 400 V | LV |
🎛️ Key Design Considerations
When designing ELV and LV systems under IS 10101, engineers must consider:
Correct voltage classification
Appropriate protective measures
Separation between ELV and LV circuits
Equipment ratings and insulation
Earthing and fault protection
Misclassification can lead to non-compliance and safety risks.
🎛️ Final Thoughts
IS 10101 clearly defines ELV and LV to ensure electrical installations are designed and installed safely and consistently.
Understanding the difference between these two voltage bands helps:
Reduce risk
Improve system reliability
Ensure regulatory compliance
📍 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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