The Siemens 3NJ6900-4HG11 is a moving-iron analogue panel ammeter for the SENTRON 3NJ6 series of in-line switch disconnectors with fuses. It provides true RMS current indication on a 250 A scale via a 250/1 A current transformer input — the highest current rating available in the 3NJ6900 pluggable ammeter family.

250 A: The Top of the 3NJ6900 Range

At 250 A, this ammeter serves the largest fused-switch feeders in low-voltage distribution — main incomers for small-to-medium installations, large sub-distribution panels, and dedicated supplies for major equipment such as chillers, compressors, and industrial machinery lines. The 250 A scale with Class 1 accuracy provides ±2.5 A resolution at full scale — sufficient for operational monitoring of load balance, demand trends, and overload verification. The 1 A secondary is the natural choice at this current level, where the feeder CT is typically located in a cable compartment or busbar chamber at some distance from the instrumentation panel.

Decision Parameters