Access Control Wire Chart
Every circuit at the door, wired right: readers (with the Wiegand-versus-OSDP distance and security story), lock power, contacts, and REX. OSDP facts are the SIA OSDP v2.2.2 / IEC 60839-11-5; gauges and distances are manufacturer specs with real variance — where mfrs disagree, the chart says so instead of averaging.
Wiring by circuit
| Circuit | Gauge | Conductors | Max distance |
|---|---|---|---|
| Reader — Wiegand | 18–22 AWG, shielded | 6 typical (5–10) | 500 ft (18 AWG); many mfrs derate 22 AWG to 250 ft |
| Reader — OSDP (RS-485) | 24–18 AWG twisted shielded pair | 1 pair data + power as needed | 4,000 ft at ≤9,600 baud (falls with speed); 120 Ω termination |
| Lock power (maglock / strike) | 18 AWG minimum, size by voltage drop | 2–4 (18/4 in composites) | Voltage-drop limited — see the DC drop chart |
| Door contact (DPS) | 22 AWG | 2 | Long (one mfr publishes 1,000 ft) |
| Request-to-exit (REX) | 22 AWG | 4 typical (power + contact) | Same as inputs |
Typical lock current draws (mfr-typical)
| Device | @ 12 VDC | @ 24 VDC |
|---|---|---|
| Maglock, 600-lb class | 500 mA | 250 mA |
| Electric strike (typical range) | 150–450 mA | 120–250 mA |
The composite cable
The standard “access control composite” bundles the whole door in one pull: 22 AWG multi-pair shielded — reader; 18/4 — lock power; 22/4 — REX; 22/2 — door contact. Exact reader element (22/6 vs 22/3-pair) varies by brand; roles are fixed. One jacket, one pathway, four circuits — and the reader element's shield still grounds at one end only. Lock-power legs size on the DC voltage drop chart, and where the door hardware ties into fire alarm release, the fire alarm interface charts take over.
Common questions
What is the maximum distance for a Wiegand reader?
500 ft is the industry ceiling — at 18 AWG shielded. Several manufacturers derate 22 AWG to 250 ft (though at least one major reader maker publishes 500 ft at 22), so the honest answer is the reader datasheet. Practical installs stay well under the ceiling; past it, the answer is OSDP.
Why switch from Wiegand to OSDP?
Four reasons that all show up on real jobs: distance (4,000 ft vs 500), security (AES-128 (Secure Channel) — Wiegand transmits card data in the clear and is trivially skimmed), supervision (OSDP constantly monitors the wiring; a cut Wiegand run is silent), and multidrop (several readers share one RS-485 bus). Terminate the bus with 120 Ω and mind the baud-rate-vs-distance tradeoff.
What wire do you use for a maglock?
18 AWG minimum, sized by voltage drop — a 600-lb maglock draws about 500 mA at 12 V (250 mA at 24 V), and lock makers design their wire charts at a 5% drop while devices tolerate ±10%. Run the actual numbers on the DC voltage drop chart; 24 V power quadruples the workable distance for the same lock wattage.
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