Correct Answer

Concept & PrincipleElectricalPower System

Option C

Increases

Quick Summary: A loose connection in an earthing circuit increases the contact resistance at the joint, which directly adds to the total resistance to earth. According to Ohm's law, an increase in resistance at any point in the conductive path between the equipment and the earth electrode results in a higher overall resistance for the earthing system.

💡 Explanation

A loose connection in an earthing circuit increases the contact resistance at the joint, which directly adds to the total resistance to earth. According to Ohm's law, an increase in resistance at any point in the conductive path between the equipment and the earth electrode results in a higher overall resistance for the earthing system.

🔢 Key Formulas

$R_{total} = R_{c} + R_{e}$ — where $R_c$ is the contact resistance and $R_e$ is the earth electrode resistance

$V_{touch} = I_{f} \times R_{e}$ — demonstrating that higher $R_e$ increases touch voltage during faults

⚙️ Working Principle

Earthing resistance ( $R_e$ ) is the sum of electrode resistance, soil resistance, and the contact resistance of all joints in the path ( $R_{total} = R_{electrode} + R_{joints} + R_{soil}$ ). When a connection is loose, the effective contact area between the conductors is significantly reduced, creating high-resistance localized junctions. This creates a bottleneck for fault current flow, thereby increasing the total path impedance.

📌 Key Points

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Loose connections are a primary cause of high resistance measurements in routine maintenance audits.
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High earthing resistance prevents protective relays and MCBs from operating correctly during a ground fault.
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Loose joints are prone to sparking and localized heating under high fault current conditions.
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Periodic checking of all earthing terminal tightness is mandatory as per electrical safety standards.

✅ Advantages

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Ensures low-impedance path for fault currents
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Minimizes step and touch potential

❌ Disadvantages / Limitations

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Increased risk of electric shock
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Potential for equipment damage due to voltage spikes

🛠️ Applications / Uses

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Industrial earthing systems
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Lightning protection systems
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Telecommunication grounding grids

📄 Additional Information

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Standard requirements often specify that earthing resistance should be as low as possible, typically below 1 Ohm for major stations.
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Option A is incorrect because resistance is directly dependent on the integrity of the conduction path.
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Option B is physically impossible as a loose connection increases the barrier to electron flow rather than reducing it.

📊 Diagram / Illustration

✅

C is correct — A loose connection decreases the contact surface area, leading to an increase in the electrical resistance of the grounding path.

Core Concepts Used

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Contact Resistance Earthing System Integrity Ohm's Law

💡 EXAM TIP

When troubleshooting earthing resistance, always inspect physical connections (nut-bolt tightness) before assuming the soil resistivity has changed due to environmental factors.

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