An important part of any circuit is the over current protection—fuse or circuit breaker. Over-current devices are used to prevent the conductors from overheating. Remember: when electricity passes through a resistance, heat is produced and a voltage drop occurs. As the electrical load on a circuit increases, the heat produced increases and the voltage drop increases. An electrician determines the total amperage capacity of the circuit and then installs the appropriate over-current protection. In the case of an overload or a short in the circuit, the over-current device stops the flow of electricity by opening the circuit. If the over-current device burns out or trips, the circuit has been overloaded. The load on the circuit must be reduced or the short repaired before the circuit is energized.
An additional protection device required by most codes for residential use is the Ground Fault Circuit Interrupter (GFCI). A GFCI constantly monitors the difference in the current between the hot conductor and neutral conductor. When the difference reaches 5 mA the GFCI trips and opens the circuit. This provides more protection to the user of metal cased tools and when using electrical appliances around water. Some Agricultural Engineers also recommend GFCI's be installed in circuits used around animals. This is especially true for very valuable animals.
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