Publish Time: 2025-12-26 Origin: Site
Cutouts are crucial in protecting power distribution lines from overloads and short circuits. Whether they are installed on overhead lines or pole-mounted transformers, they ensure reliable service continuity and reduce downtime.
In this article, we'll reveal the basics of applying and using cutouts. Understanding these is essential to enhancing electrical system performance.
A cutout fuse is a protective device that combines a fuse and a disconnect switch used to safeguard equipment such as transformers and overhead lines from faults and overloads.
The drop-out fuse cutout is a common type of cutout. It contains three key components: (1) an insulator body made from either porcelain or polymer, (2) a fuse tube, which is designed to withstand high temperatures and mechanical stress during fault interruption, and (3) the hinge which connects the fuse tube to the insulator body, allowing the tube to ‘drop out' when the fuse link melts.
The basic principles of operation are as follows:
Normal operation: During normal operations, current flows through the fuse link inside the fuse tube.
Fault or overload occurs: When there is an overload or short circuit, the fuse element heats up.
Fuse link melts: During this heat-up, the fuse link melts, creating an arc.
Dropout mechanism: After the arc is formed, the fuse tube drops out from the hinge assembly, creating a visual indication that the circuit has been interrupted.
Replacement and restoration: Once the fault has been cleared, the fuse link can be inserted into the fuse tube and closed to restore power.
Not all cutouts are built the same. However, here are some common cutouts and their applications:
Expulsion fuse cutout: This cutout has an expulsion mechanism that extinguishes the arc formed when a fuse link melts during a fault current. It is commonly installed in distribution networks for transformer protection. It is also installed in rural and urban installations for feeder line protection and in overhead distribution line isolation.
Polymer fuse cutout: This cutout uses silicone rubber or composite insulators to provide durability, reduced weight, and excellent pollution resistance. It is installed in high-humidity or coastal regions. It is also installed in polluted industrial zones and areas where frequent maintenance is difficult.
Porcelain fuse cutout: This cutout offers high mechanical strength and excellent thermal stability in high-temperature environments and heavy-duty applications. This is why it is installed in outdoor areas.
Before applying or using cutouts, ensure the operating personnel are properly trained in maintenance and safety practices. Provide them with safety glasses, hard hats, hot sticks, and rubber gloves. Ensure that only trained and authorized personnel handle cutout operations.
Regular training reduces human error and improves confidence when performing replacement or installation. It also extends the lifespan of electrical assets by following practices that comply with safety regulations.
Do not install cutouts inside enclosed spaces or directly above transformers. When a fault occurs, the fuse expulsion releases hot gases and high-velocity particles. Limiting the flow of gases with enclosed installations can cause flashovers, heat buildup, or secondary arcing, which could eventually damage equipment and personnel.
Mount cutouts in open, well-ventilated areas that allow clear dropout movement. This can prevent injury and property damage.
The fuse holder ratings must match those of the fuse link. For example, a 100-amp fuseholder should be used with a fuse link with a rating of 100 amps or less. A 200-amp fuse holder should be used with fuse links rated above 100 amps and up to 200 amps. In some specific cases, fuse links above 100 amps may fit into a 100-amp fuseholder bore, but may not operate effectively.
Furthermore, some fuse links rated 100-amp or lower may fit 200-amp fuseholders but may not clear the fault-current window within the cutout rating. Thus, ensuring the ratings match guarantees proper coordination with protective devices and safe power distribution.
Do not leave a fuseholder open for an extended period of time. An open fuseholder can lead to excess moisture ingress, which could damage the fuseholder liner. Eventually, this could cause it to swell and affect its ability to activate when there is a fault.
In all cases, the fuseholder should be removed when the cutout tap is left open. Keep it in a dry place or hang on on the pole in an upright position. Clean and check the contacts and replace contacts that are missing.
In choosing cutout ratings, look at the maximum recovery voltage, operating voltage of the system, continuous current, minimum level of basic insulation, and fault-current levels. It is important to remember that polymer cutouts can be used in high-polluted areas, whereas porcelain can be used in low-polluted areas.
Environmental pollutants may lower the performance of insulation. Regular inspection is highly essential, particularly in places with extreme contaminants, such as salt, dust, or industrial remains. Make sure that the surfaces of contacts do not have any residue.
Wipe the insulator body using a damp cloth, a soft cloth, or a mild cleaning solution to avoid flashovers and large leakage currents. Do not scratch the insulators.
The link ejector latch ensures secure placement of the fuse link and reliable dropouts during faults. When installing or replacing a fuse link, ensure the ejector latch is properly engaged and aligned. Rotate the link ejetor about its pivot until it engages with the hinge contact. An improper latch may overstress the fuse link when the fuseholder is in a closed position.
Furthermore, it may prevent the fuse link from dropping out during a fault, posing a safety risk for equipment and personnel.
Carefully wind the fuse link cable in a clockwise direction around the threaded stud. Ensure the smaller cables are wound close to the stud base so that they are not severed when the nut is tightened. Cut off any excess to prevent flashover and keep the fuseholder in place.
Use only non-abrasive tools to avoid damaging the fuse link insulation. Do not tighten the nut above 175 in.-lb. This ensures a stable electrical connection, preventing contact resistance buildup over time.
Every time you re-fuse a fuse tube, check it for signs of burning, deformation, or arcing. Always replace the fuseholder if it shows excessive erosion or if the fiber liner wall is cracked. A damaged fuse tube can cause dielectric failure under voltage stress.
Clean the surface and ensure the venting mechanism. Follow the manufacturer's guidelines to replace the fuse tube when and as necessary, such as when there is carbonization or structural damage.
When replacing components, always use approved replacement parts. Substituting with unauthorized parts can change the mechanical fit and compromise fault interruption capacity. For example, replacing a fuseholder cap that has an arc-shortening rod with a cap that does not have one will reduce the fault interrupting capacity.
Always check for signs of venting or cracking, and replace immediately if any are detected. Before replacement, confirm part compatibility with the model number on the cutout's nameplate or consult the manufacturer's data.
Do not open a non-load-break cutout to interrupt load current. Doing so can cause injury or equipment damage. Use cutouts designed to break the load current or use loadbreak devices. For linkbreak cutouts, use fuse links requiring less than 1 inch of elongation before breaking. Using fuse links requiring more than 1 inch can cause the fuseholder to drop out while still carrying current.
Therefore, ensure proper rating to prevent flashovers, injury, or severe arcing. This will improve the safety of personnel and equipment while enabling safe disconnection under fault.
During interruption, hot gases and particles are typically forced out of a fuseholder. This may cause severe damage. Thus, stay away from the vented end and exhaust path of the cutout.
Rotate the fuseholder to an intermediate position, looking away from the cutout. Slide the fuseholder, quickly and firmly, to the closed position, and take care not to damage the reinforcing material of the ring when taking off the disconnect stick.
Installation of a fuse link should be done carefully to avoid twists or abrasions. In accordance with ANSI requirements, fuse links are expected to resist up to 10 pounds of stress. Any pulling force in excess of 10 pounds may damage the element. Therefore, do not stretch or overtighten the link.
Ensure that the tension spring and contact points are placed correctly, and then close the fuse tube. Correct installation provides proper fault interruption and minimal downtime.
The small auxiliary tube of the fuse link is not part of the packaging. Do not remove it as it serves a critical function. It is used to clear low fault currents that the main element alone cannot interrupt. Removing or damaging it can compromise the cutout's ability to interrupt a fault.
Always leave it intact and place it in the right position as supplied by the manufacturer. During inspection, verify its secure attachment before reinstallation.
Follow the manufacturer's loadbreak instructions when using loadbreak tools. Each model has specific procedures to ensure proper arc suppression. Ignoring these instructions can lead to incomplete fault interruption or equipment damage.
If the fuse link blows frequently, this could be caused by incorrect fuse rating, short-circuiting, or transformer inrush current exceeding the fuse's time-current curve. This can be solved by verifying the system ratings and replacing the fuse link with the appropriate rated type.
Carbonization could be caused by repeated arcing due to partial discharge or moisture ingress. Replace the affected fuse tube. Inspect the terminals to prevent moisture ingress and clean the surrounding hardware to reduce pollution buildup.
If the dropout mechanism fails to activate, this could be caused by mechanical wear or incorrect installation. Clean and lubricate the contact points. Verify alignment and replace damaged metal fittings.
Corrosion could be caused by high pollution, salt fog, or chemical exposure. For the porcelain cutout, clean the surface with a mild cleaning solution. For the polymer cutout, use clean water and inspect for loss of moisture.
Applying and using cutouts requires proper training, safety practices, and adherence to the manufacturer's specifications. However, this will guarantee reliable performance and extended lifespan of your electrical system.
Contact Haivol Electrical for premium cutout fuses and expert guidance.
Some of the basic factors to consider include normal operating current, operating voltage, interrupting rating, inrush currents, the physical size, and mounting.
The difference between a fuse and a cutout is in their function. A fuse is a component that melts to break a circuit during an overcurrent. A cutout is a device that houses the fuse link and includes a switch that can be opened during a fault.
Cutouts should be inspected regularly, at least monthly, and a deeper inspection should be done annually. However, the frequency of inspection depends on the type of cutout, its environment, and its usage.
To choose the right cutout, match the system's voltage and current. Consider the environmental factors, material, and application type.
Home Products Solutions Technical Resources News Sustainability About Us Contact
Surge Arrester Insulator Fuse Break Swtich Overhead Line Hardware Fittings Cable Accessories