How an EPABX Is Wired: MDF Box, Rosettes and Telephone Cable

Short answer: an EPABX is wired as a star. Every phone gets its own run of telephone cable back to the exchange, the cable ends in a rosette (wall socket) next to the phone, and in bigger setups all the cables first land on an MDF box beside the exchange so they can be tested and re-patched. For a typical 8-phone office the main cabling parts come to ₹4,846 on our store; prices include GST and delivery across India is free.

This guide is about the wiring only. If you are still choosing the exchange, start with the EPABX intercom system guide or the EPABX price list, then come back here before your electrician starts cutting walls.

What are the parts of an EPABX wiring job?

There are only five things between the exchange and the phone on a desk.

• The exchange (EPABX). It has LINE or CO ports for outside telephone lines and EXT ports, one per extension. A 108 has 1 line port and 8 extension ports.
• Telephone cable. Thin multi-pair copper cable. Each extension needs one pair (two wires). A 2-pair cable gives you one working pair and one spare.
• MDF box. MDF stands for main distribution frame. It is a wall box with terminal strips where every room cable ends near the exchange. Short jumpers then connect each room to an EXT port.
• Rosette. A small socket box fixed on the wall at each phone point. The cable from the wall is screwed into it, and the phone plugs into its RJ11 socket.
• RJ11 cords. The short patch leads with the small clear plug. They join the rosette to the phone, or the exchange port to the MDF.

How does the wiring layout work?

Think of the exchange as the centre of a wheel. Each phone is at the end of its own spoke. You cannot loop one cable from room to room and tap phones off it, the way you would with an electrical circuit. Each extension number belongs to one EXT port, so it needs its own pair all the way back.

The outside line works the other way round. The landline from your telephone provider comes into the building once and goes to the LINE port. If you also use broadband on that line, a splitter at the entry point separates the internet signal before it reaches the exchange.

When do you need an MDF box?

For two to four phones close to the exchange you can run each cable straight into the EXT port. Once you cross about eight phones, the CCL installation notes on our EPABX listings recommend an MDF box, and it makes sense: eight or more cables arriving at one small exchange become hard to trace. Our 10-pair MDF distribution box is a mild steel, vertical wall-mount box listed for landline telecom distribution. Ten pairs cover an 8-extension exchange with two spare. For 16 extensions or more, plan for two boxes side by side.

How to wire an EPABX, step by step

1. Mark every phone point. Walk the building and list each desk, room, gate cabin and store. That count is your extension number, and it decides the exchange size.
2. Fix the exchange location. A dry, ventilated indoor wall near the incoming landline and a power socket, as the CCL listings advise. Fix the MDF box right next to it.
3. Measure each run. Measure from the MDF to every phone point along the route the cable will actually take, through conduit or along the ceiling. Add a couple of metres at each end. Add the runs up to know how many rolls of cable you need.
4. Pull one cable per phone. Use 2-core or 2-pair telephone cable, never mains wire. CCL's notes ask for a gap of about 30 cm from mains wiring. Run it in its own conduit where you can.
5. Label both ends. Write the room name or extension number on the cable at the MDF end and at the rosette end. This one habit saves hours later.
6. Terminate the rosettes. Screw the working pair into the rosette terminals. Fold the spare pair back neatly inside so it can be used if the first pair ever fails.
7. Terminate at the MDF. Punch or screw each room cable onto the MDF strip in order: room 1, room 2 and so on, matching your label list.
8. Patch to the exchange. Connect each MDF position to the matching EXT port with jumper wire or RJ11 leads. Connect the landline to the LINE port.
9. Test before you programme. Plug a phone into each rosette. Check dial tone, call another extension, then make one outside call. Only after every point works, set extension numbers and call restrictions as the exchange manual explains.

Have a trained electrician do the cable pulling and termination. Our team will guide you on WhatsApp through the patching and programming at no charge.

How much cable do you need?

Our TW-2P telephone wire comes as a 90 metre, 2-pair roll with PVC insulation and single-strand copper conductors. It is listed for intercom, EPABX and fax use. As a rough planning rule: average run length multiplied by number of phones, plus about 10 percent for bends and wastage, divided by 90 gives the number of rolls.

Example: an office with 8 phones and an average run of 15 m needs about 132 m of cable, so two rolls. A 16-room guest house with 20 m average runs needs about 352 m, so four rolls. CCL also states that each extension should stay under 600 ohms loop resistance, which on good telephone cable allows runs of hundreds of metres, so distance is rarely the problem in a home, shop or office.

Wiring parts on our store

Part	What the listing says	Use it for	Price
TW-2P telephone wire	90 m roll, 2 pair, PVC, single-strand copper	Runs from MDF or exchange to each phone	₹1,799
ROS-11 rosette box	Single-line rosette, pack of 10	Wall socket at every phone point	₹349
MDF distribution box	10 pair, mild steel, vertical wall mount	Termination point beside the exchange, 8+ phones	₹899
RJ11 cords, set of 10	1.5 m, RJ11 both ends, 26AWG 4-core, flat cable	Rosette to phone, port to MDF patching	₹449
RJ11 cords, set of 20	1.5 m, RJ11 both ends	Larger jobs, 16 extensions and up	₹849
TSPL-12 ADSL/VDSL splitter	Splits one line into phone and broadband modem	Landline that also carries internet	₹160

Worked example: cabling for an 8-phone office

Item	Qty assumed	Amount
TW-2P telephone wire, 90 m	2 rolls (8 runs of about 15 m)	₹3,598
ROS-11 rosettes, pack of 10	1 pack (8 used, 2 spare)	₹349
10-pair MDF box	1	₹899
Total cabling material		₹4,846

Add the exchange and phones on top. For a 1-line, 8-extension office that could be the CCL 108 at ₹3,799, whose listing says it ships with 9 RJ11 leads, or the plainer CCL 108B at ₹3,200. Electrician labour is extra and depends on your city and the building.

Common wiring mistakes

• Looping one cable through several rooms. Each extension needs its own pair back to the exchange.
• Sharing conduit with mains. It causes hum on calls. Keep telephone cable in its own pipe.
• No labels. Without them, a single fault means testing every cable.
• Loose patch cords. Check the RJ11 plug before blaming the exchange.
• Exact-fit sizing. Pull one or two extra cables to likely future points while the walls are open.

Browse all cabling parts in EPABX gateways and accessories and cables and wires, and exchanges in EPABX systems. Planning an office or shop with locks and alarms as well? The security system builder puts it all in one list. For calling over a network instead of telephone cable, read the IP-PBX vs EPABX guide.

FAQ

Which cable is used for EPABX wiring?

Standard 2-core or 2-pair telephone cable with copper conductors. One pair carries one extension; the second pair of a 2-pair cable is a spare. Do not use mains or speaker wire.

Is an MDF box necessary for an EPABX?

Not for two to four phones near the exchange. From about eight phones upward it is strongly recommended, because it gives you one neat place to terminate, test and re-patch every room cable.

Can two phones share one cable from the EPABX?

Two phones on the same pair will act as one extension and ring together. If you want separate extension numbers, each phone needs its own pair running back to its own EXT port.

How far can an extension phone be from the EPABX?

CCL specifies under 600 ohms loop resistance per extension, which allows runs of hundreds of metres on good telephone cable. For runs between buildings, use cable in conduit and protect it from water.

What is a rosette in telephone wiring?

A rosette is the small wall socket at the phone point. The telephone cable is screwed into its terminals, and the phone plugs into its RJ11 socket with a short cord.

Do I need a splitter for the EPABX landline?

Only if the same landline also gives you broadband. Fit the splitter where the line enters, send the phone side to the EPABX LINE port and the modem side to your router.

Prices are NavKar Systems website prices on 27 October 2026, inclusive of GST, and may change.