Protective conductor monitoring

Protective conductor monitoring is an inverter protection function. It detects when the grounding (PE) conductor is missing or wired incorrectly, and when that happens it disconnects the inverter from the utility grid. On SMA inverters this condition shows up as event 9 or event 901. To troubleshoot, inspect all of the AC cabling, especially N and PE. Look for loose terminals and confirm the conductors are landed on the correct terminals. Measure the N-PE voltage at the inverter and at the sub-distribution. It must be below 0.3 V on TN-C grids and below 30 V on TT grids. On other grid types it can also be deactivated to stop false trips, but only after consulting the local grid operator. A second protective conductor may then be needed as well. During SMA commissioning, check that the grounding conductor is connected to ground, for example at a grounding busbar or a foundation ground electrode. On TN systems, also measure to confirm a conductive connection between neutral and the grounding conductor. If the event keeps appearing after the AC installation has been checked, contact SMA Service. Have ready the device type and serial number, the grid type, the N-PE readings, and whether the monitoring is switched on or off.