The Siemens 3NJ6900-4HB11 is a moving-iron analogue panel ammeter designed as a pluggable accessory for the SENTRON 3NJ6 series of in-line switch disconnectors with fuses. It provides direct-reading current indication on a 50 A scale with Class 1 accuracy, drawing only 0.6 VA from the measurement circuit via a 50/1 A current transformer input.

Moving Iron: True RMS by Design

The moving-iron mechanism responds to the RMS value of the current directly — not the average value like a rectifier-type meter. In modern low-voltage distribution systems where harmonic currents from VSDs, LED lighting, and switch-mode power supplies distort the waveform, a moving-iron ammeter reads the true heating effect of the current without the errors that affect average-responding meters. This makes it the technically correct choice for circuits with non-linear loads.

Pluggable Design for Simple Retrofit

The 3NJ6900 ammeters plug directly into the 3NJ6 switch disconnector body — no separate wiring, no additional panel cutout, no external mounting brackets. They can be added to an existing installation at any time, converting a basic switch disconnector into an instrumented feeder monitoring point in seconds.

Decision Parameters