Decades ago, the electrical system in homes used fuses to protect the electrical circuits and equipment from and electrical short or overload. An electrical short or overload occurs when there is a direct pathway to ground in an electrical circuit. When this occurs, large amounts of electrical current will flow in the circuit including the wiring, connections, and the electrical fixture. High current flow causes heat to increase in the circuit. Wires, switches, outlets, connections, etc will heat up. When these components pass high current, they will also begin to heat up. As they heat up, resistance in the wire or component increases. The resistance limits the amount of current that can flow. The result of all this behavior is that current will reduce as the resistance increases, but the heat generated will increase. When components get hot enough, they can ignite combustible material nearby. Due to this, an electrical short can cause a fire or can electrocute someone.

To protect electrical circuits a device needs to be installed between the electrical source and what is known as the load.  The load is the electrical device, switch, outlet, wiring, etc. The device limits the amount of current that can flow. These devices will fail or open the circuit to stop the current flow.

In modern homes, circuit breakers are used to protect equipment and components. When the current passing through a circuit breaker exceeds a specified value, the circuit breaker will trip. This action opens the circuit, stops the flow of current, and helps to protect occupants and the home.

In older homes, the electrical protection devices used were fuses or fusible links. These types of protection devices will melt an internal wire which creates an open circuit. The open circuit stops the flow of current thus protecting the circuit. 

The home shown in the video has the outside AC condenser with the fuses replaced with copper tubing. This removed the protection from the circuit. In this particular case, the main electrical panel had been updated with a newer panel at some point in the past. The protection for electrical circuits changes from fuses to breakers in the panel. The correct update would have been to removed the old fuse protection AC disconnect and install a modern disconnect that has a removable plate. This removable plate will disconnect electrical power from the outside AC unit to allow service personnel to work on the unit.

During inspections, unusual installations like this are often found . When dealing with electrical items and electrical equipment, doing it safely should always be the #1 consideration. However, the requirement or need to reduce the costs for the work, often forces corners to be cut 

In this video, I looked in the AC condenser disconnect and the fuses had been replaced by copper pipe. This is very dangerous if there is not current protection in the main electrical panel. If the fuse is smaller than required by the condenser manufacturer, you can get nuisance trips where the start up current burns the fuse. Techs would put these pipes in to prevent the fuse from burning through. Very dangerous. 

On the bright side here, a correctly sized breaker was installed in the main panel protecting the condenser. 

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