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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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The least expensive protection for over current in low-voltage system is
Rewirable fuse
Isolator
Circuit breaker
Air-break switch
Rewirable fuse
Quick Summary: A rewirable fuse, commonly known as a kit-kat fuse, is the most cost-effective overcurrent protection device for low-voltage systems. It utilizes a simple fuse element (usually tinned copper wire) that melts when the current exceeds its rating, thereby breaking the circuit.
A rewirable fuse, commonly known as a kit-kat fuse, is the most cost-effective overcurrent protection device for low-voltage systems. It utilizes a simple fuse element (usually tinned copper wire) that melts when the current exceeds its rating, thereby breaking the circuit.
H=I2Rt — Heat generated in the fuse element
If≈k⋅d1.5 — Preece's law relating fusing current If to wire diameter d
The device operates on the principle of the thermal effect of electric current (I2Rt). When an overload or short-circuit occurs, the heat generated in the fuse element causes it to fuse or melt due to its low melting point. Once melted, the current flow is interrupted, protecting the circuit from further damage.
Most widely used in domestic and small-scale industrial low-voltage installations.
The fuse element is typically made of tin, lead, or copper wire.
Requires manual replacement of the wire once it blows.
Offers low breaking capacity compared to MCBs or HRC fuses.
Extremely low initial cost
Simple construction and easy to maintain
Readily available spare parts
Lower accuracy in breaking time
Susceptible to oxidation and aging
Cannot handle high fault levels compared to HRC fuses
Domestic lighting circuits
Small single-phase motors
Temporary distribution boards
| Feature | Rewirable Fuse | Circuit Breaker |
|---|---|---|
Cost | Very Low | High |
Reusability | Replacement required | Resettable |
Circuit breakers (Option C) provide superior protection and are resettable but have a significantly higher initial installation cost.
Isolators (Option B) are designed for manual switching only and do not provide protection against overcurrent.
A is correct — The rewirable fuse is the most economical solution for providing overcurrent protection in low-voltage distribution systems.
Always remember that while rewirable fuses are cheapest, they offer the least precision; always recommend MCBs for sensitive electronics or high-value residential loads.