TNC TNS TNCS are all TN systems, which are our commonly used civil building lighting power systems.
The first T represents the power terminal grounded. The second N represents the N line, that is, the equipment end is grounded through the power supply.
TNC is a three-phase four-wire system. The neutral line N and the protection line PE are combined into one, and the equipment is terminated with the N line.
TNS is a three-phase five limiter, that is, the N line is separated from the PE line, and the equipment terminal is connected to the PE line for grounding.
TNCS combines PNC and PNS, leads out the PEN line, separates the N line and PE line at the equipment end, and connects the equipment to the PE line for grounding.
There are also IT and TT systems. The first I represents that the power supply is not grounded, and the second T represents that the equipment itself is grounded.