The Siemens 3NJ6900-4HE12 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 150 A scale via a 150/1 A current transformer input, with Class 1 accuracy and 1 VA burden. The 2-fold overload capacity accommodates inrush and intermittent high-current conditions.

Bimetal at 150 A: Thermal Response for Mixed Loads

A 150 A feeder typically serves aggregated loads — multiple HVAC units, pump groups, or process equipment that cycle on and off. The bimetal mechanism integrates current over time with its inherent thermal time constant, showing the operator the sustained heating trend rather than flickering with every load change. This is the information that matters for thermal management of cables, busbars, and fuse elements.

Decision Parameters