In a TN-C-S earthing system, what is the PEN conductor?

• A. It is a dedicated earth conductor only from the source
• B. It is a combined protective earth and neutral conductor used in part of the system
• C. It is a local earth electrode only at the consumer
• D. It is a separate live conductor used for protection

Answer: (B)

In a TN-C-S earthing arrangement, one conductor carries both protective earth and neutral functions for part of the installation. This combined conductor is called the PEN conductor. It provides the neutral return path and an earth path for faults up to the point where the installation splits into separate protective-earth (PE) and neutral (N) conductors. After that split, the PE and N run separately to carry their respective roles safely. It’s not just an earth path, and it isn’t a separate live protective conductor; its job is to serve both earth and neutral in the portion of the system before the split.