Siemens 3RT5956-1CD00 is a SIRIUS RC-element surge suppressor. It handles DC 150 to 250 V and AC 127 to 240 V at 50 Hz, or 240 to 127 V at 60 Hz.
The DC voltage range of 150 to 250 V is the critical selection parameter: this suppressor is intended for contactor coils with a rated control voltage falling within that band. If your coil is 24 VDC, this part will not suppress — the RC element won't conduct enough to clamp the transient. The AC range covers 127 to 240 V at 50 Hz and 240 to 127 V at 60 Hz, which maps to common global line voltages (127 V line-to-neutral in some markets, 240 V line-to-line in others). The AC/DC type of voltage means the same unit works on either supply, but the DC range is the tighter constraint. Storage range of -40 to +80 °C is broader, governing shelf life before installation. The part is rated for 50 Hz and 60 Hz operation, so it works on either mains frequency without derating.
As a snap-on accessory for SIRIUS contactors, this RC suppressor mounts directly onto the coil terminals of the matching contactor — no additional wiring or DIN-rail space required. It adds negligible depth to the contactor assembly, so fill factor in the enclosure stays unchanged. Verify the contactor frame size: the 3RT5956-1CD00 is designed for the SIRIUS range; check that the contactor's coil voltage falls within the suppressor's DC or AC range before ordering.