3RT1975-6A New Original Siemens 3RT19756A Switchpieces Contact Piece

Part Number: 3RT1975-6A

Manufacturer: Siemens AG (Germany)

Product Type: Replacement Contact Kit (Spare Part)

Product Range: SIRIUS (3RT1 Series)

The 3RT1975-6A is the Siemens OEM replacement contact kit for the SIRIUS 3RT1075 power contactor. It contains everything needed to restore the main contact assembly of one 3RT1075: three movable contact bridges, six fixed contact pieces, and the associated mounting hardware.

The kit replaces all six contact surfaces across the three main poles simultaneously—restoring the contactor to its original contact resistance, voltage drop, and current-carrying capacity.

The 3RT1075 is Siemens' size S12 power contactor, the largest standard frame in the SIRIUS 3RT1 range. Rated at 400A AC-3, it switches three-phase AC motors up to 200kW on 400V networks, 150hp on 480V, and 400hp on 600V supplies.

At these power levels, the 3RT1075 handles some of the highest continuous currents in the SIRIUS product line. It appears in large motor control centres, main drive panels for industrial fans and compressors, central pump drives in water treatment, and heavy marine and process applications.

The contacts take significant wear—making the 3RT1975-6A one of the most important servicing spares for any site running these machines.

SIRIUS design philosophy keeps contact replacement practical. The 3RT19 kit series allows maintenance without removing the contactor from the panel in many installation types—the modular body gives direct access to the contact assembly. That means less downtime, fewer disconnections, and a faster return to service.

Each time the 3RT1075 opens under load, an arc forms between the separating contacts. The arc lasts a fraction of a millisecond—but at 400A, the energy in that interval is significant. It erodes a tiny amount of contact material with every operation.

The eroded material deposits as black carbonised residue on the contact surfaces. Over hundreds or thousands of switching cycles, this erosion accumulates. Contact thickness decreases. The contact pressure spring deflects less. Surface geometry changes from flat and smooth to pitted and irregular.

These changes drive up contact resistance. Higher contact resistance means more heat generated at the contact joint—which accelerates erosion.

The warning signs are clear: elevated temperature at the main terminals, visible pitting, the smell of heated metal during heavy switching, and in advanced cases, the sound of a harder-than-usual arc on closing.

Left unaddressed, worn contacts eventually weld—the softened silver-alloy surfaces fuse during an interruption event. A welded contactor cannot open under fault conditions and presents a safety hazard. Regular inspection and timely kit replacement with the 3RT1975-6A prevents this outcome.

A common cost-cutting instinct is to replace only the most worn pole. It is the wrong call. When one pole reaches the wear threshold, the other two are close behind—at 200kW and above, all three phases carry nearly equal current and experience nearly equal arc energy per cycle.

Replacing only one pole means the remaining two will need replacement soon, requiring a second shutdown and a second maintenance event.

Full kit replacement with the 3RT1975-6A takes the contactor back to a uniform baseline across all poles. The next maintenance interval is predictable and consistent. The total labour cost is lower—one intervention instead of two.

The 3RT1975-6A fits within Siemens' structured SIRIUS spare parts programme. The 3RT19 contact kit product line covers most SIRIUS 3RT1 contactor frame sizes, with specific kit part numbers for each frame size and current rating.

Alongside the contact kit, Siemens offers coil replacement kits (3RT1975-5AB series for various coil voltages) and arc chute replacement options, making the 3RT1075 a fully serviceable unit rather than a throw-away device at end of contact life.