The Main Duties of a Cutout
The Three Important Duties of a Fused Cutout
By Michael Murphy
If you look up at the electrical distribution lines overhead, you are likely to see a fused cutout. That little device has been modified and improved over the last 80 years to become the product electric utilities all around the world use today. This product has become widely used because the fused cutout has three main jobs which this article will explain.
Duty 1: Fused protection for a line asset (often a transformer)
A fuse can be installed inside of the fuse holder, also called a fuse tube. Like the breakers in your home, a fuse installed before a transformer will protect it from over current conditions. For example, a 30A fuse link can be installed in the cutout fuse holder. Then if the transformer draws 40 amps for any more than a few seconds the fuse will operated, effectively disconnecting the transformer from the electric line and protecting the transformer from harm. After this happens the fuse holder will fall open. The open fuse holder provides an easy to see visual indication that the fuse had operated. That means a linemen can quickly find and replace the fuse.
Duty 2: Ground fault current protection.
The cutout will also operate and open the circuit in the case of a downstream ground fault. For example, if a tree falls on a power line, this would cause a ground fault. All the available energy will try to rush to the ground. This is dangerous and the circuit must quickly be opened. The current that will try to rush through the cutout and to ground can be more than 10,000amps. The cutout stops the flow of energy by quickly extinguishing an arc which is generated inside the fuse holder. After the arc is extinguished the fuse holder will fall open. Again, the open fuse holder provides a visual indication that the fuse had operated and must be replaced.
Duty 3: Visual indication of an open circuit
Regardless of the cause if the fuse cutout operates the fuse holder will hang open signaling to the linemen that the line must be serviced. This seemingly simple duty is one of the most important jobs of the cutout.
As you can see the fused cutouts found overhead preform valuable duties all of us. These little devices save electric utilities millions of dollars a year by preventing damage to transformers and other line assets. Also the cutout saves utilities thousands of hours a year by making it easy to see where a line needs to be serviced. This also means in the case of a power outage electricity can be restored more quickly. The humble fused cutout keeps the light on and saves us all money.