DELTA Cat 3 junction box — two universal RJ11/12/45 ports. Each accepts the full range of registered-jack plugs without an adapter: RJ11 (6P4C, single-line phone), RJ12 (6P6C, two-line phone or ISDN So bus), and RJ45 (8P8C, ISDN, DSL, or 10BASE-T Ethernet).

When is Cat 3 still the right choice in 2026?

Two scenarios: (1) the building already has Cat 3 cable in the walls and you are replacing broken outlets, not rewiring — the socket must match the cable class; (2) the drop is a dedicated voice/DSL line where higher categories add cost without benefit — a fax line, an elevator emergency phone, a DSL modem jack, or a POTS connection to a legacy BMS dial-out modem. In these cases, Cat 3 is not a compromise — it is the correct specification.

Why an RJ45-sized socket for a phone line?

The UAE (Universal Anschluss Einheit) standard used in German electrical installation deliberately uses an 8-pole form factor for telecom sockets. This means an RJ45 Ethernet cable can be plugged in for DSL or ISDN — but the wiring behind the socket (only 2 or 4 wires terminated per port, not all 8) is what limits the speed. The socket itself does not reject Ethernet plugs; the Cat 3 wiring behind it is the bottleneck.

Can I use this for Ethernet?

Only 10BASE-T (10Mbit/s). Cat 3 is rated for 16MHz — insufficient for 100BASE-TX (requires Cat 5, 100MHz). If you plug a Gigabit Ethernet device into this socket, the link will either negotiate down to 10Mbit/s or fail to establish a link at all, depending on the switch. For Ethernet at any speed above 10Mbit/s, use a Cat 6E junction box (5TG2026-1 or 5TG2026-2) instead.

Claw-and-screw fixing vs. screw-only fixing

This insert supports both mounting methods. Screw fixing is standard for solid masonry walls with flush boxes. Claw fixing (Krallenbefestigung) grips the inside of the flush box when screw holes are stripped or when retrofitting into older boxes without matching screw positions. The combination means this insert installs in practically any DIN 60mm flush box ever made.