What part of a metal water pipe entering the building is permitted to serve as part of the grounding electrode?

The grounding electrode system is a critical component in ensuring safety and proper grounding in electrical systems. When it comes to metal water pipes entering a building, the National Electrical Code (NEC) specifies requirements for how these pipes can function as grounding electrodes.

The correct answer indicates that the first 5 feet of a metal water pipe can be used as part of the grounding electrode system. This provision encourages effective grounding by utilizing the metal water pipe, which is often in contact with the earth, thus providing a low-resistance path for fault current.

Using the first 5 feet of the pipe allows for a reliable grounding point while also ensuring that any potential corrosive materials or damage that may occur further in the line does not impact the effectiveness of the grounding. It should be noted that grounding electrode conductors should be connected to this portion if continuous grounding is desired.

The other options suggest longer lengths of pipe could serve as grounding, which exceeds the NEC guidelines. The specific limit set by the NEC not only addresses safety and functionality but also reflects best practices to minimize the chances of corrosion and maintain effective grounding.