PEN Conductor Break (Elevated Potential, TN-C-S)

A fault condition in the TN-C section of a TN-C-S network (for example an underground or overhead distribution cable using a combined neutral-earth conductor) in which the PEN conductor is interrupted between the transformer and the point where it splits into the installation, for example due to corrosion, excavation damage or a poor connection. Because both PE and N are derived from the PEN conductor after the split point, a PEN break not only causes the neutral conductor to lose its earth reference, but also raises all earthed metal parts (enclosures, conduit, PE cores) of the connected installations to a potential equal to the load imbalance in the network — in severe cases nearly the full phase voltage, with direct electrocution risk on touching normally earthed parts. This risk is a key reason why, in the Netherlands, new installations preferably use TN-S from the connection point onward, and why PEN conductors in distribution networks must be more heavily dimensioned and better monitored than an ordinary N conductor.