Bus cable
Bus cable is screened data cable for fieldbuses and building automation. RS-485 cable has one or two 120 ohm twisted pairs (110 ohm for the B2ca version) under foil and braid, for Modbus RTU among others. It comes in four versions: LSZH, UV-resistant PE, B2ca and armoured. For KNX/EIB there is the green cable to the KNX specification. Q Cables supplies to order, with the lead time stated in the quote.
Types in this category
RS-485 1×2×0.20 LSZH
RS-485 bus cable, 1 pair 0.20 mm², 120 Ω, foil and tinned-copper braid, LSZH sheath
Lead time: On request; the lead time is stated in the quote.
RS-485 2×2×0.20 LSZH
RS-485 bus cable, 2 pairs 0.20 mm², 120 Ω, foil and tinned-copper braid, LSZH sheath
Lead time: On request; the lead time is stated in the quote.
RS-485 1×2×0.22 LSZH B2ca
RS-485 bus cable, 1 pair 0.22 mm², 110 Ω, foil and tinned-copper braid, blue LSZH sheath, B2ca-s1a,d0,a1
Lead time: On request; the lead time is stated in the quote.
RS-485 2×2×0.22 LSZH B2ca
RS-485 bus cable, 2 pairs 0.22 mm², 110 Ω, foil and tinned-copper braid, blue LSZH sheath, B2ca-s1a,d0,a1
Lead time: On request; the lead time is stated in the quote.
RS-485 1×2×0.20 PE UV
RS-485 bus cable, 1 pair 0.20 mm², 120 Ω, foil and tinned-copper braid, UV-resistant PE sheath
Lead time: On request; the lead time is stated in the quote.
RS-485 2×2×0.20 PE UV
RS-485 bus cable, 2 pairs 0.20 mm², 120 Ω, foil and tinned-copper braid, UV-resistant PE sheath
Lead time: On request; the lead time is stated in the quote.
RS-485 1×2×0.22 SWA PVC
RS-485 bus cable, 1 pair 0.22 mm², 120 Ω, foil and tinned-copper braid, steel wire armoured, PVC sheath
Lead time: On request; the lead time is stated in the quote.
KNX/EIB bus cable
KNX/EIB building-automation bus cable to the KNX specification, J-Y(St)Yh 2×2×0.8, green
Lead time: On request; the lead time is stated in the quote.
What makes a bus cable different
An RS-485 bus cable carries data, not power. What counts is the characteristic impedance: it has to match the terminating resistors at the ends of the bus, otherwise the signal reflects. RS-485 (EIA/TIA-485) is designed for 120 ohm cable. Our RS-485 cables are 120 ohm, or 110 ohm ±15 ohm for the B2ca version. The pair is twisted and runs under foil plus a tinned-copper braid, against interference from frequency converters and motor cables. Do keep a distance from motor cables and cross them at right angles.
RS-485 is the physical layer under Modbus RTU and BACnet MS/TP, among others. The standard allows 32 unit loads per bus; with lower-load transceivers, more devices can be connected. At lower speeds a bus can run to around 1,200 m. Lay the bus as a line from device to device, not as a star, and terminate the line at both ends with a resistor equal to the cable impedance: 120 ohm, or 110 ohm for the B2ca version.
KNX/EIB: a cable of its own
KNX TP uses a cable of its own to the KNX specification: two pairs of solid 0.8 mm cores under a foil screen, with a green sheath. One pair carries the bus, the second is a spare. The cable is tested at 4 kV and may run right next to sheathed mains cables. In boxes and distribution boards, keep loose bus cores at least 4 mm away from mains cores. An RS-485 cable is no substitute for it, and the reverse is also true.
CPR class per version
The versions differ mainly in sheath and fire class. The grey LSZH and the armoured SWA PVC are Eca, the UV-resistant PE version is Fca and the blue LSZH is B2ca-s1a,d0,a1. Where the cable is exposed to indoor air in a building, the Bbl requires at least Dca; there you choose the B2ca version. It also complies in an extra protected escape route, where the Bbl requires B2ca with smoke class s1. The KNX cable is Eca in PVC; the halogen-free version is Cca, on request.
| Type | Voltage | CPR | Standard | Conductor | Availability and lead time |
|---|---|---|---|---|---|
| RS-485 1×2×0.20 LSZH | 300 V | Eca | EIA/TIA-485 | Stranded tinned copper, 7 × 0.19 mm (±0.008 mm), approx. 0.20 mm² | On request The lead time is stated in the quote. |
| RS-485 2×2×0.20 LSZH | 300 V | Eca | EIA/TIA-485 | Stranded tinned copper, 7 × 0.19 mm (±0.008 mm), approx. 0.20 mm² | On request The lead time is stated in the quote. |
| RS-485 1×2×0.22 LSZH B2ca | 600 V | B2ca-s1a,d0,a1 | EIA/TIA-485 | Stranded tinned copper, 7 × 0.20 mm, approx. 0.22 mm² | On request The lead time is stated in the quote. |
| RS-485 2×2×0.22 LSZH B2ca | 600 V | B2ca-s1a,d0,a1 | EIA/TIA-485 | Stranded tinned copper, 7 × 0.20 mm, approx. 0.22 mm² | On request The lead time is stated in the quote. |
| RS-485 1×2×0.20 PE UV | 300 V | Fca | EIA/TIA-485 | Stranded tinned copper, 7 × 0.19 mm (±0.008 mm), approx. 0.20 mm² | On request The lead time is stated in the quote. |
| RS-485 2×2×0.20 PE UV | 300 V | Fca | EIA/TIA-485 | Stranded tinned copper, 7 × 0.19 mm (±0.008 mm), approx. 0.20 mm² | On request The lead time is stated in the quote. |
| RS-485 1×2×0.22 SWA PVC | 300 V | Eca | EIA/TIA-485 | Stranded tinned copper, 7 × 0.20 mm (±0.008 mm), approx. 0.22 mm² | On request The lead time is stated in the quote. |
| KNX/EIB bus cable | 250 V | Eca | DIN VDE 0815 (J-Y(St)Yh) | Solid bare (plain) annealed copper, 0.8 mm diameter, class 1 acc. to IEC 60228 | On request The lead time is stated in the quote. |
Which cable for Modbus RTU?
Modbus RTU usually runs over RS-485. You then choose a screened 120 ohm twisted pair, such as our RS-485 cables. Alongside the data pair, the Modbus specification requires a third conductor as a common reference (Common). For a two-wire bus you therefore choose the two-pair cable: one pair for the data, the second for the Common. Four-wire Modbus needs two data pairs plus the Common; please mention this in your enquiry.
How long can an RS-485 bus be?
At lower speeds an RS-485 bus can run to around 1,200 m. The higher the baud rate, the shorter the bus. What counts is the total length of the line; keep stubs as short as possible.
Can bus cable be laid outdoors?
Yes, with the RS-485 version with a UV-resistant PE sheath. Where mechanical damage is a risk, choose the armoured version. The PE version is Fca: where the cable runs into a building, the Bbl requires at least Dca there.
Instrumentation cable: PiMF, TiMF and screening
When individual screening pays off and when a collective screen is enough.
Read the article →Cca, Dca or B2ca: which CPR class for your project
What the classes mean, which one the Bbl requires and what the choice does to price and lead time.
Read the article →Quote
Request bus cable
State the bus system (for example Modbus RTU or KNX), the number of pairs, indoors or outdoors and the CPR class the specification asks for. We will get back to you with type, price and lead time.
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