The Siemens 3NJ6900-4HD11 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 100 A scale via a 100/1 A current transformer input — the higher-current counterpart to the 50 A 4HB11, sharing the same moving-iron measurement principle, Class 1 accuracy, and 0.6 VA burden.

100 A Rating for Main Feeders and Sub-Distribution

The 100 A scale serves a common rating in low-voltage distribution: sub-main feeders, larger motor circuits, HVAC equipment supplies, and lighting distribution boards. This ammeter plugs directly into the 3NJ6 switch disconnector body, providing local current indication without the cost or complexity of a digital meter — a practical choice when the operator simply needs to verify that the feeder current is within normal range.

1 A Secondary for Extended Wiring Runs

The 1 A secondary input reduces resistive losses in the CT secondary loop to 4% of what a 5 A circuit would produce at the same wire gauge (P = I²R). This matters in larger installations where the switch disconnector may be in a remote feeder pillar and the instrument is in a centralized monitoring panel — the 1 A design maintains accuracy over longer cable distances.

Decision Parameters