While testing the Earth Fault Loop Impedance ( EFLI ) of one of the rooms, it was observed that the EFLI value was 20.1 ohms, and the Prospective Fault Current was only 11A. The EFLI value at the Main Switchboard was also the same, which raised seriouWhen planning the construction of a building, we often rely on various consultants for Mechanical, Electrical & Plumbing, Air Conditioning, Civil, Structural, Architectural, and more. Sometimes, we might combine these responsibilities and rely on a single consultant or even a contractor. We believe that everything is safe and sound until a problem arises. In electrical projects, we usually depend on a contractor, and sometimes we may not seek a second opinion if we trust them too much. However, this may not always be sufficient.
Recently, we were invited to conduct an electrical safety audit in India at a new commercial building equipped with a 1000 KVA 11KV / 415V Transformer, a 1000 KVA DG set, and a connected load of 1.3 MW. The quality of electrical installation was commendable as it was carried out by a reputable contractor, and the overall performance was good except for one critical issue: the Earth Fault Loop Impedance (EFLI) value.
What is Earth Fault Loop Impedance?
Earth fault loop impedance is the measure of the total resistance in the electrical circuit path that allows fault current to flow during an earth fault condition. It includes the impedance of all components in the fault path, such as the power source, conductors, protective devices, and the earthing system itself. This measure is crucial for ensuring that sufficient fault current flows to trigger protective devices promptly, thereby isolating the fault and preventing hazards like electric shocks, fires, or equipment damage.
Earthing Effectiveness of the Facility
As per prevailing practice, the facility has multiple earth pits, including:
- 4 earth pits for the Transformer ( 2 for Neutral, 2 for Body )
- 2 earth pits for HT panel boards and switch gears
- 4 earth pits for the DG set
- Multiple earth pits for the field area, including 2 earth pits for the Lightning protection system
- Multiple earth pits for UPS systems, IT systems, and others
s concerns about the high loop impedance value.
The Danger of High EFLI Values
When the EFLI value is high, during an earth fault, the fault current will be low, and the protective devices will either not operate or will take more time to respond. This delay can cause significant damage to the electrical system, including fire hazards. Hence, a very low EFLI value is essential for all electrical circuits.
Immediate and Long-term Solutions
To address this critical issue, we recommended connecting all earth pits as a ring main to form a Main Earth Terminal (MET). This was initially connected in a temporary manner for testing purposes. As a result, the EFLI value dropped from 20.1 ohms to 0.3 ohms, and the fault current increased from 11 amps to 3.1 kiloamps, which is sufficient to trigger protective relays during a fault.
Learning from the case study
This case highlights the importance of conducting thorough electrical safety audits, especially for new premium properties. Relying solely on contractors may not always ensure complete safety. Advanced diagnostic techniques like thermal imaging (thermography) and periodic electrical safety audits, ( for healthcare facilities hospital electrical safety audits ) are crucial for maintaining electrical safety and compliance. With effective implementation of recommended measures, we can ensure the safety and reliability of electrical installations, preventing potential hazards and ensuring peace of mind for all occupants.
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When a load is plugged in, if the plug top or socket is getting warm, it can be due to loose connection in plug socket or top, or improper contact area of male and female contacts. During Electrical safety audits, such issues can be easily identified using Thermal imaging and exact reasons for getting heated up can be identified.