Fuse and circuit breaker are both protection devices. Although they are used for circuit safety, there are many differences between them. Let’s take a look at the differences between these two devices.
Differences between fuse and circuit breaker
Fuse vs circuit breaker:
Fuse is an overcurrent protective device with a circuit opening fusible part that is heated and severed by the passage of overcurrent through it.
Circuit breaker is a device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating.
The independent breaking capacity of a circuit breaker is small compared to the fuse, but incorporating the cascade method with the upstream circuit breaker can increase the breaking capacity. A current limiting mechanism is required to achieve a large breaking capacity.
A mechanism with a large breaking capacity can be manufactured quite easily. The breaking test must be verified with the fuse and knife switch combination.
Adjustable trip characteristics
For all but the smallest circuit breakers, adjustable trip settings are available that can help provide optimal levels of selective coordination and arc-flash protection in a system. Electronic trip units provide the highest degree of setting flexibility. Trip characteristics of a fuse cannot be adjusted.
The entire unit of the circuit breaker is enclosed, so when switching a load current, the arc is not discharged. In addition, this type is safe as the live section is not exposed. The contact switching speed is constant regardless of the handle switching speed. The load current can be switched safely.
Overload and short-circuit current are tripped inside the fuse tube, however, with many units the arc is discharged when switching the load current. In many structures, the live section is exposed.
Phase failure protection
Even if the overcurrent flows only to one pole of the circuit breaker, all poles are simultaneously disconnected, so there is no possibility of phase failure.
If the overcurrent flows to only one pole of a fuse, only that pole blows, and a phase failure results (single-phase operation takes place). The motor, etc., could burn.
Load switching capacity
In addition to switching the rated current at the rated voltage, the circuit breaker has the ability to switch a current six times the rating 12 times or more.
Switching of the rated current at the rated voltage is limited in the fuse.
Normal use is possible in the circuit breaker, even after tripping an overload current. So, there is no need to keep a constant supply of spare parts.
The fuse must be replaced after a short-circuit accident or overload operation, so a constant supply of spare parts is required.
It is easy to reactivate the circuit breaker immediately after an overload has occurred. The circuit breaker is simply reset after the fault is corrected. No extra steps or procedures are required for recovery as with the fuse.
The fuse must be replaced after the cause of the accident is removed; thus, it takes time for recovery (the power failure will continue).
A slight change in operating characteristics after tripping a short-circuit current is permitted in the standards. However, the operating characteristics of a circuit breaker will not change with a normal overload, etc.
If a current exceeding the deterioration characteristics flows to the fuse, the fuse will deteriorate, the operating characteristics will change, and the unit may malfunction.
Remote operation of a circuit breaker is possible by operating the electricity. Elements required for automatic control, including the undervoltage trip, voltage trip, auxiliary switch and alarm switch, etc., are built-in.
A fuse cannot be operated remotely.
Protective characteristics and operating characteristics
Sufficient load protection is provided overall ranges as the circuit breaker characteristics can be checked, and there is no worry of degradation, and the tolerance in respect to load currents can be small. The characteristics are achieved with a combination of the time-delay characteristics and instantaneous characteristics. In addition, each function independently, so characteristics matching the load are achieved.
In view of deterioration, etc., the fuse’s rated current must be increased with respect to the load current. Thus, it may not be possible to protect the load in low over-current ranges. Only the thermal element of the fuse is used, so the characteristics cannot be adjusted according to the load.
When selecting a circuit breaker, an allowance of 10 to 20% in respect to the load current is given in consideration of the load equipment’s total load current variation and effect of the ambient temperature, etc.
With the fuse, there is a concern of deterioration, so the fuse rating must be approximately double the load current value.
There are various types of connections available in the circuit breaker including front surface, back surface, inserted, and embedded.
Typically, only the surface type is available in the fuse. This is inconvenient when designing panels.
Maintenance and inspection
The circuit breaker is easy to handle and does not require much maintenance or inspection. But fuses must be inspected regularly.
The trip button is a pushbutton for mechanically tripping the circuit breaker from the outside. A circuit breaker with a trip button can be easily tripped by pressing the trip button. A fuse cannot be opened from the outside.
The one-time cost of a fuse can be less expensive than a circuit breaker. And that gap rapidly widens at higher ratings!
A circuit breaker can also double as a power disconnect in many applications. Especially if you’re working with equipment that requires regular service, this can be a convenient feature. In these cases, you can even find breakers that include lockout/tagout facilities.
Most circuit breakers come equipped with a visual indicator that alerts users when they’ve tripped. This tool can reduce diagnostic time and help you get straight to the source of the electrical issue. If you find it difficult to remember to check fuses, this can be an important benefit.
A wide variety of circuit breakers are available—from relatively basic molded-case circuit breakers to the “top of the line” low-voltage power circuit breakers—with optional features that make them appropriate for nearly any application. Many of these features are not available on fusible systems without the addition of external metering equipment, relays, or other accessories.
Replacing fuses requires the door of the panel to be open. This creates a situation where potential live voltage contact is possible. To make the situation worse, some fuse clips and fuses are completely accessible from the front. What’s more, replacing a power fuse requires a trained electrician, which can delay production until one can arrive on site. Some fuse blocks require a fuse puller or a special tool for servicing, which aren’t usually provided or readily available. This can lead to a potentially dangerous situation if someone attempts to remove a fuse with an incorrect tool like a metal screwdriver. With breakers, it’s easier to make maintenance and commissioning.
Usage in DC circuits
There are increasingly more DC circuits in today’s modern panels, with the growing acceptance of alternative energy and the EV market. There’s also a trend toward changing 120 VAC controls circuit to 24 VDC for safety reasons, in case of accidental contact with live voltage. Breaker technology has improved and is now capable of handling DC circuits.
As machines deliver more feedback and information than ever before, industrial applications need circuit protection that can go the extra mile. Breaker technology is ready for these advanced applications. Fuses are losing popularity day by day.