| Full title | EN 50090 series, Home and Building Electronic Systems (HBES). TP1 bus: EN 50090-5-2, Part 5-2: Media and media dependent layers, Network based on HBES Class 1, Twisted Pair |
| Publisher | CENELEC, committee CLC/TC 205, with KNX Association as co-operation partner. International series: ISO/IEC 14543-3 (ISO/IEC JTC 1/SC 25) |
| Specification owner | KNX Association, founder and owner of the KNX Standard, which maintains the KNX specifications and runs product certification |
| Current edition (TP1) | EN 50090-5-2:2020, published April 2020, replacing EN 50090-5-2:2004. National withdrawal date for conflicting standards: 10 April 2023 |
| Status | EN 50090-5-2:2020 published and current. EN 50090-9-1:2004 (installation requirements) withdrawn by CENELEC with effect from 1 February 2017. BSI still lists BS EN 50090-9-1:2004 as current |
| Related standards | BS 7671, BS EN 50174-2, EN 50288 and EN 50290 cable series, ISO/IEC 11801-6 |
What it covers
KNX is an open protocol for home and building control: lighting, blinds, heating, ventilation, metering and similar functions. Its protocol and media are published as the European EN 50090 series and as parts of the international ISO/IEC 14543-3 series. The KNX specifications were also published by CEN as EN 13321-1 and EN 13321-2.
The KNX Association, founder and owner of the KNX Standard, maintains the KNX specifications and runs the certification scheme for KNX products. EN 50090-5-2:2020 states that it was prepared with the help of the KNX Association as a CENELEC co-operation partner.
This page covers twisted pair, known as TP1, which carries data and power on one pair of wires.
Structure of EN 50090
| Part | Subject |
|---|---|
| Part 1 | Standardisation structure |
| Part 3 | Aspects of application |
| Part 4 | Media independent layers (for example EN 50090-4-2: transport, network and general parts of the data link layer for HBES Class 1) |
| Part 5 | Media and media dependent layers (EN 50090-5-2: TP1) |
| Part 6 | Interfaces |
| Part 7 | System management |
The EN 50090-5-2:2020 foreword lists these parts and notes that Part 2 has been withdrawn.
Installation part (withdrawn)
EN 50090-9-1:2004, Installation requirements: Generic cabling for HBES Class 1 Twisted Pair, gave rules for planning, engineering, installing and commissioning Class 1 twisted-pair cabling. It covered cable supports, cables, connectors and coexistence with mains power and other networks. CENELEC withdrew it with effect from 1 February 2017. No replacement is listed. BSI still lists BS EN 50090-9-1:2004 as current.
International series
ISO/IEC 14543-3 is the international counterpart, prepared by ISO/IEC JTC 1/SC 25. Its first parts were published in 2006. For example, ISO/IEC 14543-3-1:2006 (edition 1.0) specifies the application layer for network based control of HES Class 1.
TP1 system parameters
Table 1 of EN 50090-5-2:2020 gives the main system parameters. They apply only to cable that meets the bus cable requirements in the standard (subclause 4.4) and to devices drawing no more than 12 mA from the bus.
| Characteristic | TP1-64 | TP1-256 |
|---|---|---|
| Medium | Shielded twisted pair (shield not mandatory) | Same |
| Topology | Linear, star, tree or mixed | Same |
| Baud rate | 9600 bps | 9600 bps |
| Power supply unit | 30 V DC | Same |
| Power supplies per physical segment | Maximum 2 | Maximum 2 |
| Devices per physical segment | Maximum 64 | Maximum 256 |
| Total cable length per physical segment | Maximum 1000 m | Maximum 1000 m |
| Distance between two devices | Maximum 700 m | Maximum 700 m |
| Device bus consumption | 3 mA to 12 mA | Same |
| Protection against shock | SELV | SELV |
A TP1-64 segment can be extended with up to three more physical segments through bridges, giving a line of up to 256 devices. TP1-256 is backwards compatible with TP1-64. Line couplers join lines into a zone, and backbone couplers join up to 16 zones.
A logical 1 is the idle state of the bus. The standard gives a bit time of 104 µs and a DC level of 21 V to 32 V for a logical 1.
Bus cable requirements
EN 50090-5-2:2020 sets bus cable requirements in subclause 4.4. Its normative references include the EN 50290 communication cable series, IEC 60189-2, IEC 60332-1 and IEC 60754-2. The KNX Association certification scheme uses a Manufacturer’s Declaration on KNX Cables, which lists these values:
| Property | Value in KNX cable declaration |
|---|---|
| Conductor diameter | 0.8 mm to 1.0 mm, copper, solid or stranded |
| Pairs and colours | Two pairs: red/black and white/yellow |
| Maximum cable length | 1000 m (standardised cable) |
| Loop resistance | 20 to 75 ohm/km (standardised cable) |
| Capacitance, wire to wire | 10 to 100 nF/km at 10 kHz |
| Twist | Minimum 5 twists per metre |
| High voltage test | 2 kV AC, 50 Hz, or 4 kV AC where a country requires it |
| Core to core withstand | 800 V AC |
| Environmental and mechanical | Relevant parts of EN 50288 or EN 50290 |
The declaration also lists a screen over the whole cable diameter with a drain wire of at least 0.4 mm, and requires an outer sheath. A cable that is not standardised may have a shorter maximum length, which must be stated in its documentation. EN 50090-5-2 Table 1 does not make a shield mandatory.
SELV and separation from mains
TP1 operates under SELV conditions. In UK installations, BS 7671 sets requirements for segregating circuits of different voltage bands. BS EN 50174-2 gives separation rules for information technology cabling from power cabling. See the library pages for those standards. CENELEC has withdrawn the EN 50090 installation part (EN 50090-9-1).
What it means in practice
- Use bus cable that meets subclause 4.4 of EN 50090-5-2. The 1000 m and 700 m limits apply only to such cable.
- Keep each physical segment to 1000 m of cable in total and no more than 700 m between any two devices.
- Check whether devices are TP1-64 or TP1-256 before planning more than 64 devices on one segment. Use no more than two power supply units per segment.
- Segregate the bus from mains circuits as required by BS 7671. For separation from power cabling, see also the BS EN 50174-2 rules for information technology cabling.
- EN 50090-9-1 was withdrawn by CENELEC in 2017, but BSI still lists BS EN 50090-9-1:2004 as current. Confirm with the specifier before citing it.
Related reading: KNX cable explained · What is control cable?.