The Siemens 3NJ6900-4HB22 is a bimetal analogue panel ammeter for the SENTRON 3NJ6 series of in-line switch disconnectors with fuses. It provides thermal-response current indication on a 50 A scale via a 50/5 A current transformer input — combining the overload-tolerant bimetal mechanism with the industry-standard 5 A secondary interface.

Bimetal + 5 A: The Practical Combination for Motor Feeders

This variant pairs two practical features: the bimetal mechanism tolerates the starting inrush of motors (typically 6-8× rated current for several seconds) without needle damage or calibration drift, while the 5 A secondary is compatible with the CTs most commonly found in motor control centers and industrial distribution panels. For a 50 A motor feeder where the operator needs to see running current — not the starting spike — this is the correct instrument choice.

Within the 3NJ6900 Matrix

The 3NJ6900 family offers eight combinations across two current ratings (50 A, 100 A), two measurement principles (moving iron, bimetal), and two secondary ratings (1 A, 5 A). The 4HB22 occupies the bimetal / 50 A / 5 A position — identical in measurement principle to the 4HB12 (bimetal / 50 A / 1 A) but with the 5 A secondary interface preferred in brownfield installations with existing 5 A CTs.

Decision Parameters