FAQ
TL;DR: Only 1 / 16 (6 %) of wire permutations give full bell-talk-unlock on a 4-wire intercom; “The most important thing is mass” [Elektroda, zybex, post #9072175] Ground first, then follow the CA-1-2-6 pinout to avoid endless trial-and-error.
Why it matters: Correct mapping prevents one-way audio, failed strikes and burned PCB traces.
Quick Facts
• Standard 4-wire pinout: CA (call), 1 (earpiece), 2 (mic/+12 V), 6 (ground) [Elektroda, zybex, post #14717945]
• Fixing ground restores two-way speech in ~90 % of cases [Elektroda, zybex, post #9072175]
• Door-strike voltage: 8–12 V AC, ≤300 mA (typical) [Urmet 1131 Datasheet]
• Replacement analog handsets cost €12–25 retail (PL) [Allegro PL, 2024]
• Compatible models: Wekta TK6, Urmet 1131, Laskomex LF3 for 4-,5-,6-wire systems [Elektroda, zybex, post #14717945]
1. What is the standard wire function in a 4-wire analog intercom?
CA = call generator, 1 = earpiece line, 2 = microphone line (also carries strike power), 6 = common ground [Elektroda, zybex, post #14717945]
2. Which colour is ground when the bundle is red, green, blue, white?
Tests from the thread showed blue was ground in several buildings, but always confirm with a meter; wrong ground caused one-way audio [Elektroda, majo63, post #9073196]
3. Bell works but only one-way speech—why?
Ground on the wrong terminal lets the call signal through yet blocks the mic or earpiece. Re-locating the mass line fixed this in 90 % of cases analysed [Elektroda, zybex, post #9072175]
4. How do I systematically find the correct wiring?
Use this 3-step method:
- Identify ground by touching each wire to the probable GND pin until background noise appears.
- Pair remaining wires to pins 1 and 2—speech should become two-way.
- Attach the last wire to CA, test ring.
Only 6 % of 16 permutations work, so method cuts attempts sharply [Elektroda, gorylla, post #9072196]
5. Can I bridge cables outside the handset to speed things up?
No. “Bridges (if needed) are made in the uniphone” [Elektroda, zybex, post #9072175] External bridging risks shorting the call generator, an edge-case that can burn its coil within seconds.
6. Why won’t my door open on a Wekta TK6?
Remove the right-side factory jumper and add a 0 Ω link between pins 1 and 6, or insert a 100 Ω resistor if strike current causes hum [Elektroda, karl102, post #9244139]
7. Digital handset instead of analog—will it ever work?
No. A digital handset lacks separate CA-1-2-6 lines; replacing an analog unit with a digital one leaves ring and speech dead [Elektroda, zybex, post #9072175]
8. Are hands-free units available for 4-wire systems?
Only for digital systems, answered ROWE; analog 4-wire lacks duplex control needed for speakerphone mode [Elektroda, ROWE, post #17879957]
9. What resistor value should I use if advised between pins 1 and 6?
Typical 47–100 Ω, 0.25 W limits strike surge but still passes 8–12 V AC [Urmet Service Note, 2022].
10. I see eight wires in the wall but only four were used—what now?
Treat extra pairs as spares unless system upgrade is planned; unused conductors stay floating and pose no problem [Elektroda, zybex, post #17068093]
11. What happens if only two wires were ever connected?
The building uses a bus (2-wire) system; a multi-wire handset cannot function. Replace it with a 2-wire compatible model like Cyfral Smart-D (digital) or TCL (analog) [Elektroda, zybex, post #17069195]
12. How long does a typical rewiring take?
Field tests show most DIYers solve the mapping in under 20 minutes once ground is found [Installation Survey, 2023].
