Electrical Test Reliability Reliability & Maintenance Center

Choose to Fuse (And Why)

Jane Alexander | January 13, 2017

Designed as sacrificial devices in electrical systems, fuses protect costlier components in those systems from the damaging effects of overcurrent. They can also make control systems UL- and NEC-compliant.

Fuses are sacrificial devices that help protect costlier components in an electrical system from the damaging effects of overcurrent. (They can also help make control systems UL- and NEC-compliant.) To be sure, there are many other solutions for protecting electrical gear from overcurrent, including circuit breakers and protective relays. Information from Cumming, GA-based AutomationDirect (automationdirect.com), though, lists 10 reasons why end users also should consider fusing.

Safety
Overcurrent protective devices that have tripped are often reset without first investigating the cause of the fault. Electromechanical devices may not have the reserve capacity to open safely when a second or third fault occurs. When a fuse opens, it’s replaced with a new fuse, meaning the protection level is not degraded by previous faults.

Cost-effective
Fuses typically are the most cost-effective means of providing overcurrent protection. This is especially true where high fault currents exist or where small components, such as control transformers or DC power supplies, need protection.

High interrupting rating
With most low-voltage current-limiting fuses (< 600 V) having a 200,000-A interrupting rating, users are not paying a high premium for a high-interrupting capacity.

Reliability
Fuses have no moving parts to wear out or become contaminated by dust or oil.

North American standards
Tri-National Standards specify fuse performance and the maximum allowable fuse Ip and I²t let-through values. Peak let-through current (Ip) and I²t are two measures of the degree of current limitation that is provided by a fuse.

Component protection
The high current-limiting action of a fuse minimizes or eliminates component damage.

Extended protection
Overcurrent-protective devices, with low-interrupting ratings, are often rendered obsolete by service upgrades or increases in available fault current. Updated NEC and UL standards are fueling the need to install potentially expensive system upgrades to non-fused systems.

Selectivity
Fuses can be easily coordinated to provide selectivity under overload and short-circuit conditions.

Minimal maintenance
Fuses do not require periodic recalibration. That is not the case with some electromechanical overcurrent-protective devices.

Long life
As a fuse ages, the speed of response will not slow down or change. A fuse’s ability to provide protection will not be adversely affected by the passage of time.

Fuses 101

Fuses consist of a low-resistance metal or wire that is used to close a circuit. When too much current flows through the low-resistance element of the fuse, the element melts and breaks the circuit. This keeps the excessive current from continuing down the circuit to more expensive equipment.

For more information on a range of automation-related topics and solutions, including current-limiting fuses that meet UL and NEC codes, visit automationdirect.com or library.automationdirect.com.

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Jane Alexander

Jane Alexander

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