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Advantages and Disadvantages of Fused Switches


Fused Disconnects


Advantages Disadvantages
Downstream Equipment Protection Generally provide the greater protection in terms of interrupting rating and let-through, both I2t and Ipeak with the possible exception of circuit breakers with built in "limiters".
Operational

Both overload and high magnitude faults require access to the bucket by a qualified electrician to test and change fuses.

Additional downtime for fuse replacement on every low-level fault. (molded case circuit breakers (MCCBs) are re-settable on low-level faults).

No single-phase protection.
Safety

Because of fuse changing requirement for overload or fault clearing there is less likelihood of an operator re-closing into a faulted condition.

Visible blade to meet many plant safety procedures requiring observation of a "visible break" to help ensure voltage isolation is only available in industry with the fusible disconnect switch.

Due to the rejection feature of fuses, substitution of less capable fuses is impossible thus ensuring the design intentions are adhered to.
Due to fuse clip design requirements and exposed energized parts associated with visible blade disconnects there is more opportunity for contact with an energized part by individuals as well as other conducting items (tools, loose parts, etc.) Creating potential shock and fault hazards.
Cost Initial cost may be a trade-off depending upon size and type of breaker required for application.
Fuse replacement costs, particularly for low level overloads will add to the life cycle cost depending upon sizes and frequency of overload incidents.


Circuit Breakers


Advantages Disadvantages
Downstream Equipment Protection Eliminate single-phasing.
Generally provide less protection than current limiting fuses in terms of interrupting rating and let-through, both I2t and Ipeak with the possible exception of circuit breakers with built in "limiters".
Operational

Easier to diagnose trip with breaker trip indication without having to access bucket interior and testing fuses, etc. - Operator re-settable.

Common overloads and low level faults can be reset by the operator.

Safety

Far fewer exposed parts, lessen likelihood that someone or something will contact energized components.

Because of ease of resetting breakers from overload, there is less exposure required for low level faults or overload trips.


Visible blade to meet many plant safety procedures requiring observation of a "visible break" to help ensure voltage isolation is not available in molded case circuit breakers.

Because of ease of resetting breakers from overload or fault clearing, there is a greater likelihood of an operator re-closing into a faulted condition.


Circuit Breakers with Limiters


Advantages Disadvantages
Downstream Equipment Protection Generally provide equal or better protection than current limiting fuses in terms of interrupting rating and let- through, both I2t and Ipeak.
Use of limiters introduces possibility of single-phasing if re-energization occurs with one phase of the limiter blown.
Operational

Easier to diagnose trip with breaker trip indication for low level overloads without having to access bucket interior and testing fuses, etc. - Operator re-settable.

Common overloads and low level faults can be reset by the operator. Because of limiter fuses for high level faults re-closing into a high level fault is less likely.
High level faults will require fuse limiter testing and change-out by a qualified electrician.
Safety Because of ease of resetting breakers from overload there is less exposure required for low level faults or overload trips.
Visible blade to meet many plant safety procedures requiring observation of a "visible break" to help ensure voltage isolation is not available in molded case circuit breakers.



Tags: fused switches circuit breakers fused disconnects