How to install Fermax DUOX PLUS: complete guide 2026
More and more communities and homes need to upgrade from their old 4+N door entry system to a modern system with video, connectivity, and mobile call forwarding. The problem is that many installers hesitate: do new cables need to be run? Can any of the existing wiring be reused? Is it worth it, or is it better to patch things up?
The short answer is that Fermax's DUOX PLUS is designed precisely for this scenario. It's a completely digital system that works with just two non-polarized wires and, in most cases, allows the reuse of existing 4+N wiring. This means you can upgrade from an audio-only intercom to a full video door entry system with WiFi and 4G connectivity without chiseling walls or running new cables.
In this guide, we will cover the entire process: from how to assess the existing installation to the exact list of materials, including the step-by-step migration and errors to avoid.
Why Migrate from 4+N to DUOX PLUS
Limitations of the 4+N System
The 4+N system was the standard for intercoms in Spain for decades. Its name describes its wiring: 4 common wires (audio, ground, door opener, and call) plus an additional wire for each dwelling (N). This means a 20-apartment building needs 24 wires between the outdoor panel and the handsets.
The 4+N served its purpose, but it carries limitations that are hard to justify today. It does not natively support video — adapters exist, but quality is limited. It's not possible to forward calls to mobile. Programming is rudimentary (via physical micro-switches). And as components age, finding spare parts becomes more difficult because Fermax has focused all its current production on DUOX PLUS.
Advantages of DUOX PLUS over 4+N
DUOX PLUS solves all the above with a radically simpler approach. It only needs two non-polarized wires to transmit audio, video, data, and power. It doesn't matter what order they are connected in — there's no polarity, no wiring errors.
But the advantages go beyond installation:
- Integrated HD video on all monitors, with color night vision.
- WiFi connectivity on VEO-XS and VEO-XL monitors, with call forwarding to mobile via the Fermax Blue app.
- 4G connectivity with the CORA CONNECT panel, which does not depend on the building's WiFi.
- Digital programming of each terminal, with remote reprogramming capability via MyCONNECT.
- Up to 3 terminals per dwelling (e.g., a monitor in the living room and a phone in the kitchen).
- Compatibility with home automation and integrated RFID/NFC access control systems.
Existing Wiring Compatibility
This is the point that worries installers the most, and also the best news of the entire migration. DUOX PLUS is compatible with existing wiring in the vast majority of 4+N installations.
What Can Be Reused
According to Fermax's technical documentation, DUOX PLUS works with:
- Parallel cable (most common in old 4+N installations)
- Twisted pair
- UTP CAT5
- 5-wire cable (reusing two of them)
- 2-wire doorbell cable
- The 4+N cable itself (using two of the available wires)
In a typical 4+N installation, the wiring from the outdoor panel to each dwelling has at least 5 wires. For DUOX PLUS, you only need two. This means there are plenty of wires, and you can choose those in the best condition.
What to Verify Before Reusing
Not everything is usable without checking. Before confirming the existing wiring:
- Measure the continuity of the two wires you plan to use, from end to end. A cable with a ground fault or partial short circuit will cause video problems.
- Check the minimum cross-section: 1 mm² is recommended for distances up to 100 meters. For very thin old cables (0.5 mm²), the maximum distance is reduced.
- Verify the insulation condition, especially in junction boxes and conduits where humidity may have deteriorated the cables.
- Calculate the total distance between the panel and the furthest terminal. DUOX PLUS works perfectly up to 100 meters with 1 mm² cable. For longer distances, an amplifier distributor can be used.
If the wiring passes these checks, you can reuse it without issue. If not, the good news is that you only need to run two new wires (compared to the original 4+N), which is much less work.
What Must Always Be Replaced
Regardless of the cable condition, these elements are changed in every migration:
- The complete outdoor panel (the 4+N panel is not compatible with DUOX PLUS)
- All handsets/monitors (4+N terminals do not work on the DUOX PLUS bus)
- The power supply (DUOX PLUS requires its own 24V DC power supply)
- The door opener, if the existing one is not 12-24V compatible (check model)
Materials Needed for Migration
This is a typical shopping list for a standard residential community. The linked products are available at Profermax with professional pricing and 24-hour shipping.
Basic Configuration (building up to 20 dwellings, 1 entrance)
| Component | Fermax Reference | Qty. | Notes |
|---|---|---|---|
| DUOX PLUS Outdoor Panel | CORA CONNECT (ref. 7700) or Cityline depending on aesthetics | 1 | CORA includes integrated 4G |
| Flush-mounted box for panel | According to series (CORA: ref. 7703) | 1 | If existing box is compatible, reuse it |
| DUOX PLUS Monitor | VEO-XS WiFi (ref. 9449) or VEO (ref. 9445) | 1 per dwelling | VEO-XS includes WiFi for Blue app |
| DUOX PLUS Connector | Ref. 9447 | 1 per monitor | Quick connection of monitor to bus |
| DUOX PLUS Power Supply | Ref. 4860 (building) or ref. 4825 (single-family) | 1 | The 4860 for more than 4 dwellings |
| DUOX Distributor | Ref. 4845 | According to installation | Required when there is more than one branch or the distance is long |
Premium Configuration (with access control)
Add to the above list:
| Component | Fermax Reference | Notes |
|---|---|---|
| Memokey Kit (numeric keypad) | Ref. 5194 | Allows opening with a PIN code |
| RFID Proximity Reader | According to panel | For opening with proximity key |
| Proximity Keys | Ref. according to type | In packs of 10 units |
Step-by-Step Migration Process
1. Preliminary Assessment (in office)
Before going to the site, gather this information:
- Exact number of dwellings and their distribution by floor
- Number of entrances (main portal, garage, back door)
- Approximate distance between the panel and the furthest dwelling
- Type of existing wiring (if the client knows; if not, verify on-site)
- If they want a monitor with WiFi (VEO-XS / VEO-XL) or without WiFi (basic VEO)
- If they need access control (Memokey, RFID, both)
With this data, you can place the complete order at Profermax and request that the monitors be sent pre-programmed with the addresses of each dwelling — this is a free service that saves time on site.
2. Disconnecting the 4+N System
- Cut power to the old system.
- Disconnect the terminals in each dwelling (note which wire went to each, in case you need to map later).
- Remove the old outdoor panel.
- Remove the old power supply.
3. Wiring Verification
With the system disconnected:
- Identify two wires that run continuously from the panel's location to each dwelling.
- Measure continuity with a multimeter.
- Measure insulation resistance between the two wires and between each wire and ground. A low value indicates deteriorated cable.
- Mark the two selected wires for DUOX PLUS connection.
4. Installing the New System
- Mount the new outdoor panel in the existing location (use the new flush-mounted box if the old one is not compatible).
- Install the DUOX PLUS power supply in the telecommunications cabinet or on the ground floor distribution box.
- Connect the two wires between the panel, the power supply, and the risers to the dwellings.
- In each dwelling, connect the DUOX PLUS monitor using the quick connector ref. 9447.
Remember: the wires are not polarized. The connection order does not matter.
5. Programming
If the monitors are not pre-programmed, the address of each dwelling must be assigned:
- Manual method: Using the micro-switches on connector 9447, a binary number is assigned to each monitor. This is the classic method but prone to errors in large buildings.
- Programmer method: The DUOX Plus programmer (ref. 1495) allows assigning addresses from the panel, much faster and without going up to each dwelling.
- From the CORA panel: CORA panels with a screen allow direct programming from the installer menu.
Practical tip: If you place the order at Profermax, indicate the dwelling distribution when ordering. Your materials will be sent pre-programmed, ready to connect and operate.
6. Final Verification
Before closing conduits and considering the job finished:
- Check that each monitor receives calls correctly from the panel.
- Verify the video image — it should be clear, without lines or interruptions.
- Test door opening from each monitor.
- Measure voltage on the bus: it should be between 18V and 34V DC at rest.
- If there are WiFi monitors, verify that they connect to the network and that the Blue app works.
Common Mistakes and How to Avoid Them
Accumulated experience from hundreds of migrations has shown us what fails most often. Here are the mistakes to keep in mind:
Deteriorated cable that passes the continuity test but fails with signal. Continuity only measures if there's a circuit, not the cable's quality. A cable with degraded insulation can show continuity but generate interference when the digital signal passes through. If in doubt, measure insulation resistance (should be >1 MΩ).
Two monitors with the same address. This is a classic. In a 20-dwelling building, a programming error causes two apartments to share an address. Result: both ring when one is called. The solution is to verify each address before finishing, or better yet, entrust the programming to Profermax.
Undersized power supply. A power supply designed for a single-family home (ref. 4825) is insufficient for a 15-dwelling building. Each monitor consumes approximately 490 mA during conversation. For more than 4-5 dwellings, always use the building power supply (ref. 4860).
Mixing different cable cross-sections in the same stretch. If one branch has 1 mm² cable and another has 0.5 mm², the voltage drop will be uneven, and the furthest monitors may experience image problems or not turn on.
Not updating the door opener. The 4+N system's door opener may operate at 12V AC, while the DUOX PLUS system provides 12V DC. Some door openers are not compatible. Always check the door opener model and replace it if necessary.
Cost of Migrating from 4+N to DUOX PLUS
The cost primarily depends on the number of dwellings and the type of monitor chosen. As a rough guide for materials (excluding labor):
| Building | Basic Monitor (VEO) | WiFi Monitor (VEO-XS) |
|---|---|---|
| 8 dwellings, 1 entrance | ~€1,200-€1,600 | ~€1,600-€2,000 |
| 16 dwellings, 1 entrance | ~€2,000-€2,800 | ~€2,800-€3,600 |
| 24 dwellings, 2 entrances | ~€3,200-€4,500 | ~€4,500-€6,000 |
These ranges include the panel, monitors, power supply, connectors, and distributors. They do not include access control (Memokey/RFID) or labor.
To get an exact quote tailored to your project, you can contact our technical team indicating the number of dwellings, entrances, and preferred monitor type. We will send you a detailed quote within 24 hours.
Frequently Asked Questions
Can I reuse 4+N wiring for DUOX PLUS?
Yes, in the vast majority of cases. The DUOX PLUS system works with only 2 non-polarized wires and is compatible with existing 4+N wiring, provided the cable is in good condition and has a minimum cross-section of 1 mm² for distances up to 100 meters.
How much does it cost to migrate a community of 20 residents from 4+N to DUOX PLUS?
The average material cost ranges from €2,500 to €4,500, depending on the chosen monitors (with or without WiFi) and the number of entrances, excluding installer labor. At Profermax, we offer professional prices with a discount on the RRP.
Is it necessary to reprogram all terminals after migration?
Yes, all DUOX PLUS monitors require individual programming to assign them their dwelling's address. However, Profermax offers a free pre-programming service: if you indicate the dwelling distribution when placing your order, we will send you the monitors ready to install.
Can residents continue to use their old handset while the migration is underway?
No. 4+N terminals are not compatible with the DUOX PLUS bus. Migration involves replacing all dwelling terminals. However, the installation can be planned to minimize service downtime — it usually completes in a single workday for buildings with up to 20 dwellings.
Can I perform the migration in phases (some dwellings first, then others)?
It is not recommended. DUOX PLUS and 4+N are incompatible systems that cannot coexist in the same installation. The migration must be done all at once: the entire 4+N system is removed, and the complete DUOX PLUS is installed. What can be done is to initially install basic monitors (VEO) and later replace them with WiFi monitors (VEO-XS) without touching the rest of the installation.