What it is and what it fits
The 3VM9403-0JJ23 is a SENTRON TA2.4 circular conductor terminal — a wire connector designed as an accessory for Siemens 3VM molded-case circuit breakers in the 400 A and 630 A frame sizes. It handles two cables per terminal, each 70–300 mm², and accepts copper or aluminum conductors from 2/0 AWG up to 600 kcmil — covering the full range of feeder and distribution cable sizes you'd land on a 400–630 A breaker. Stripped length is 1.2 in for the smaller cable range and 2.3 in for the larger — that's the bare conductor length you need before insertion.
Integration note
This is a lug-style terminal that bolts onto the breaker's line or load side — no DIN-rail mounting, no panel cutout. The 3VM breaker itself snaps onto a mounting plate or DIN rail; the terminal is an add-on for cable termination. No control-wire tap on this version — it's a straight power connector. If you need a tap for auxiliary wiring, that's a different TA variant.