BT Telephone Master Outlet - Matt Black Rounded Edge

The Knightsbridge CL73MB is a BT telephone master outlet in matt black 304 stainless steel with a rounded edge profile. This is the primary socket in a telephone wiring installation, connecting the incoming BT line to the building's internal telephone wiring. It includes an integrated surge arrestor and R/C filter to protect against voltage spikes on the line and provide a stable connection for line testing by service providers.

Installed at the first connection point where the external telephone line enters the property, the master outlet allows BT engineers to test the line up to this socket without needing to access internal wiring. The socket accepts a standard BT plug and uses screw terminals on the rear for wiring connection. The 25mm minimum mounting box depth requirement makes it compatible with standard UK single-gang back boxes.

The rounded edge design incorporates a built-in gasket that sits between the faceplate and the wall surface, reducing dust ingress around the socket edges. The matt black finish is applied to 304 stainless steel, giving a durable low-sheen surface that resists fingerprints and minor scratches better than painted alternatives. The 87.75mm square faceplate matches the standard UK single-gang socket footprint, allowing the telephone outlet to sit alongside other wiring accessories in a consistent grid layout.

Product Specification Sheet

What is a master outlet and do I need one?

A master outlet is the primary telephone socket where the external BT line enters your property. It contains a surge arrestor and filter that protect your internal wiring and allow BT engineers to test the line. If you have an existing master socket and are replacing it, this is the correct type. If you need additional telephone sockets elsewhere in the property, those would be secondary sockets without the master components.

What back box depth is required?

A 25mm minimum back box depth is needed. The socket projects 7.5mm from the wall once fitted, giving a total depth of approximately 30mm from the wall surface to the rear of the mounting box.

Can this be used for broadband as well as voice calls?

Yes. ADSL and VDSL broadband signals travel over the same telephone line as voice calls. A microfilter is typically plugged into this socket to separate the broadband signal from the voice signal, or the microfilter may be built into the ADSL router plug.

What other finishes are available in this range?

Knightsbridge produces the rounded edge telephone master outlet in multiple finishes including polished chrome, brushed chrome, polished brass, antique brass and white. Use the search function to find other variants in stock at Niori.