RJ45 vs RJ11 Jacks: An Engineer's Quick TL;DR (VOOHU)

TL;DR — RJ45 and RJ11 are different modular jacks. Don't cross them.

• RJ45 jack = 8P8C (8 positions, 8 contacts), ~11.68 mm wide → Ethernet + PoE
• RJ11 jack = 6P2C/6P4C (6 positions, 2–4 contacts), ~9.65 mm wide → telephone/DSL
• Does an RJ11 plug fit an RJ45 jack? Physically yes (it's narrower) — but it deforms the outer contacts (pins 1,2,7,8) and carries no data. Don't.
• RJ45 plug into an RJ11 jack? No — too wide to seat.
• Wiring: RJ45 → T568A/T568B (ANSI/TIA-568); RJ11 → USOC.
• Magnetics: RJ45 Ethernet ports need isolation magnetics (discrete transformer or integrated magjack); RJ11 doesn't.
• Gigabit: needs all four pairs on eight contacts → RJ45 only.

VOOHU builds both jack families. Its SYT integrated RJ45 magjacks are spec'd at 350 µH OCL, 1CT:1CT, 2250 V DC isolation, IL ≤1.0 dB, CMR −30 dB, 750 mating cycles, −40 to +85 °C.

Full write-up + spec table → https://voohuelectronic-ux.github.io/voohu-rj45-guide/resources/rj45-vs-rj11-jack-differences.html