RJ11 or RJ45: Which Wall Socket Does Your Job Need? | TEO
An electrician wiring a home office in a new-build in Reading fitted a telephone outlet where the client wanted to plug in a wired router. Two visibly identical sockets, two completely different connectors underneath, and a second callout that should never have been needed.
Quick Answer
RJ11 sockets carry analogue telephone lines, using 2 or 4 of 6 contacts. RJ45 sockets carry Ethernet data, using all 8 contacts, wired to Cat5e or Cat6 for network speed. They look similar but aren't interchangeable: an RJ45 plug won't reliably seat in an RJ11 socket, and fitting the wrong one means a return visit.
What's Actually Different Between RJ11 and RJ45?
Both are registered jack connectors, and both look like a slightly smaller version of the other at a glance, which is exactly where the confusion starts. RJ11 is a 6-position connector, though most telephone wiring only uses 2 or 4 of those positions, and it carries a standard analogue phone line. RJ45 is an 8-position, 8-contact connector, physically larger, and it carries structured network cabling wired to Cat5e or Cat6 standard for Ethernet data.
An RJ45 plug is wider than an RJ11 socket opening, so it generally won't force home. An RJ11 plug can sometimes squeeze into an RJ45 socket and appear to click, but the pin alignment is wrong and it won't carry a working connection. Neither substitution is a reliable fix.
Master Socket, Secondary Socket or Data Point: Which Does the Job Need?
| Socket Type | What It's For | Where It Goes |
|---|---|---|
| RJ11 Master Telephone Socket | The primary incoming BT line, with the line's test socket and filter | Where the phone line enters the property, usually the hallway or under stairs |
| RJ11 Secondary Telephone Outlet | Extension wiring from the master socket to other rooms | Study, bedroom, kitchen, anywhere needing a second phone point |
| RJ45 Cat6 Data Outlet | Wired Ethernet network point, fed from a router or network switch | Home office, media cabinet, anywhere needing a reliable wired connection |
This is a genuine trade opinion rather than a spec sheet fact: for a home office or study, spec the RJ45 data outlet even if the client only mentions wanting a phone line. Most home workers end up wanting a wired network point for a desktop or a reliable video call connection within the first year, and running the cable once during a rewire is far cheaper than opening the wall again later.
Speccing a full room to match? Browse the finish ranges to keep telephone and data outlets consistent with the rest of the switches and sockets.
Browse BG Evolve →Does the Cable Behind the Socket Actually Matter?
Yes, more than the faceplate does. A Cat5e cable supports Gigabit Ethernet over short domestic runs, while Cat6 gives more headroom for higher speeds and longer runs without signal degradation. Fitting a Cat6-rated RJ45 socket onto cheap Cat5 cable, or vice versa, means the installation only performs to the standard of its weakest link, not its best component.
Trade Note: Label the cable run at both ends during first fix, socket location and cable category. On a job with multiple RJ45 points, this is the single easiest thing to skip and the single most annoying thing to work out later when nobody remembers which cable goes where.
Is This Notifiable Work Under Part P?
No. Telephone and data cabling runs at extra-low voltage and falls outside the scope of Building Regulations Part P and the BS 7671 notifiable work rules, which apply to fixed mains wiring. That said, if you're running new cable through a wall alongside a new mains socket or circuit on the same job, the mains side of that work still needs to be assessed and, where applicable, certified in the normal way. The two are simply assessed separately. If USB charging points are also going in on the same room spec, we've covered that decision separately: USB-A or USB-C Wall Socket: Which Should You Spec? Both sit within the wider British General range if you're matching the rest of the room.
Frequently Asked Questions
No. An RJ45 plug is physically wider than an RJ11 socket opening and generally won't seat properly. Even where it appears to force in, the pin alignment doesn't match and won't carry a working connection.
No. Only one master telephone socket is needed per property, at the point the BT line enters the building. Every other phone point in the property is a secondary telephone outlet, wired as an extension from the master.
No. Data and telephone cabling runs at extra-low voltage and sits outside Part P and BS 7671 notifiable work rules, which apply to fixed mains wiring specifically.
Cat6 gives more headroom for higher speeds and longer cable runs without degradation, and the cost difference over Cat5e is small on a typical domestic job. Spec Cat6 as the default unless there's a specific reason not to.
Most home workers end up wanting a wired Ethernet connection within the first year for a desktop or reliable video calls. Running the cable during the same first fix as the phone line is far cheaper than opening the wall again later.
No. The faceplate finish is purely cosmetic. Performance depends entirely on the cable category behind the socket and the quality of the termination, not which BG range the faceplate belongs to.
Fit the Right Connector the First Time
RJ11 and RJ45 telephone and data outlets across BG Evolve and Nexus, trade priced and in stock.
Browse Telephone & Data Outlets →Related News
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