The Siemens 3RH7140-1AP00 is a SIRIUS contactor relay in the S00 frame size, carrying 4 normally open auxiliary contacts and an AC-operated coil. It's the switching element you add when a main contactor's built-in aux stack runs out — or when you need a standalone relay for signal interlocking, PLC input isolation, or pilot-duty control circuits. Rated for 6 A at 24 V, 230 V, and 400 V, and 1 A at 110 V and 690 V, the contact reliability is specified for PLC-level loads — 17 V, 5 mA — so it's comfortable switching low-energy signals without the oxide-film problems that plague power contacts on dry circuits. The coil pulls 27 VA on pickup and holds at 5.4 VA, AC supply only. Surge voltage resistance is 11 kV, and insulation is rated 690 V at pollution degree 3 — standard for industrial panel environments.
The S00 footprint is 45 mm wide, 57.5 mm tall, 72 mm deep — tight enough to pack several in a row on a DIN rail without crowding the gland plate. That helps when you're squeezing relays into a shallow enclosure or a swing-frame panel. Screw-type terminals accept 2x 0.5–1.5 mm² solid or stranded, 2x 0.75–2.5 mm², or 2x 4 mm². Finely stranded wire with ferrule is supported in the same ranges. Strip and torque per the terminal markings — no special tools beyond a standard screwdriver.
The 40 E switching-element code (4 NO) is a common configuration; if your design needs NO/NC mix, check the 3RH7140 family for variants with different contact arrangements.