Free Newsletter
Register for our Free Newsletters
Access Control
Deutsche Zone (German Zone)
Education, Training and Professional Services
Government Programmes
Guarding, Equipment and Enforcement
Industrial Computing Security
IT Security
Physical Security
View All
Other Carouselweb publications
Carousel Web
Defense File
New Materials
Pro Health Zone
Pro Manufacturing Zone
Pro Security Zone
Web Lec
ProSecurityZone Sponsor
ProSecurityZone Sponsor
ProSecurityZone Sponsor
ProSecurityZone Sponsor
ProSecurityZone Sponsor
ProSecurityZone Sponsor

Cat 6 BMS cabling considerations explained by Connectix

Connectix : 14 November, 2008  (Technical Article)
Cabling systems available from Conectix for building management systems including fire detection systems and IP surveillance installations
Cat 6 BMS cabling considerations explained by Connectix
Modern buildings contain Building Management Systems (BMS) to control, measure and monitor building functions associated with power supplies, HVAC, lighting, security and temperature management. Some systems that cover an even wider range of events such as fire detection and access control have been
called Facilities Management Systems. Data centres are also intense users of BMS interfaces and control functions. In a data centre we might expect to see the following items requiring measurement and status reporting:.

* UPS - This needs to report its current, voltage, power and power factor status, battery state plus any fault condition.

* CRAC units - The Computer Room Air Conditioning (CRAC) units need to report their status of return temperature, output temperature, humidity levels and fault status such as the need to change the filters. CRAC units also contain leak detectors because of the continual condensate they produce.

* Fire detection system - Although the fire detection and suppression system is in many respects a self contained system it still needs to report its status to the BMS to control the following:.

• Open the valves to any pre-action sprinkler systems
• Shut down the HVAC
• Shut down the power
• Shut off ventilation air intakes and extracts
• Interface and communicate with the main building alarm

Other general interfaces are:.

- Underfloor flood detectors.
- Room overheat detectors.
- Door alarms.
- Room motion sensor alarm.
- CCTV IP cameras.
- Input smoke detector on ventilation ducts.
- Standby generator status.
- Smoke control damper status.

Two recent data centre projects undertaken with Connectix cabling had a total BMS connection count of 73 for the first installation of a 200 square metre computer room floor and a second with a 400 square metre floor presented no less than 99 BMS inputs.

The nature of these BMS signals tends to fall into two camps; the first is called volt free contacts (VFC) and the second presents a local area network interface of some description. The Volt Free Contact is literally a relay that is open or closed to represent a particular function, e.g. fault status - valve open or closed, etc. There is no voltage on the relay contacts; they are presenting an open or short circuit to the line. A Programmable Logic Controller (PLC) must make sense of, and take action on, the signal at the far end of the cabling.

The LAN interface family can be an Ethernet device or even industrial Ethernet, another IP based BMS LAN such as BACNet or a whole menagerie of interfaces from LONWorks to ModBus and CAN to Profibus. IP based devices tend to be star wired back to a central switch or hub whereas lower speed industrial protocols can be wired in a bus or loop fashion. There is yet another wireless method using an interface called Zigbee, although this has not yet made much of an appearance in the data centre environment.

If we consider what kind of cabling is used to implement these BMS connections then the only obvious one is for Ethernet which will use Category 5 or 6 copper cabling and exceptionally optical fibre for very large networks (eg the fire detection system control panels at Heathrow's terminal 5). The traditional method for everything else is for the installer or the installer of each major subsystem to overlay their own cabling for their own products. These cables can be twisted pairs of varying pair counts, screened and unscreened, multicore cables (ie straight wires that aren't twisted in pairs) and even coaxial or optical cable.
Another issue is whether the BMS cable needs to be mains voltage rated or not.

Under the European Low Voltage Directive cable has to be clearly marked whether it is for low voltage, typically up to 50 volts, or for higher mains voltage at typically 230 volts. Although Category 5 and 6 cable is insulation tested at up to 500 volts it is not rated as mains cable and must not be used for that purpose.

How often is a mains cable needed for BMS connections though? If a fan or a motorised valve needs power then it should be connected with a mains-rated cable. The vast majority of BMS connections (whether a LAN interface or VFC) will work very satisfactorily on Category 6 cabling.

The answer then is to install a dedicated BMS Cat 6 cable link within the computer room/data centre and bring all the connections back to a dedicated BMS patch panel in the Telecommunications Entrance Room or other suitable area. This will overcome the incessant problem of different trades overlaying their own cable around the computer room dedicated to their own hardware.

BMS connections can arise under the floor, along the wall and near the ceiling. The planning of the BMS link needs to take into account the physical location of the likely BMS connections and try to plan outlet points within two metres of the outlet. This is to try and keep patch cords to reasonable lengths although they could be up to 10 m long if necessary.

One method is to send out a number of Cat6 links around either side of the room (reference Figure 1). Two groups of 48 Cat 6 cables would normally suffice the average 200 square metre computer room. Every four metres a wall mounted quad Cat 6 outlet is installed about 1.5 m up the outside wall. These outlets can be connected to room telephones, CRAC and UPS connections, IP cameras, security, access control and a host of other monitoring requirements.

Back in the Entrance Room the cables are terminated in two 48-port Category 6 patch panels, clearly labelled as to what they are and where they are connected.

All the connections to the BMS monitoring equipment or CCTV equipment can be made at this point. To stay within the requirements of Ethernet transmission, the distances from the wall outlets to the BMS patch panel should be limited to 90 metres of cable length.

The final point to remember about dedicated BMS cabling is that all the other trades that are installing equipment on the site will be unaware of its existence and will simply install their own cables as usual. Somebody needs to take the responsibility of informing all other suppliers on the site about the BMS
common cabling and the need to use it for their own interfaces. If some suppliers refuse to use common cabling on the grounds that they will only give a warranty if they have their own dedicated cabling then it's probably time to look for a new supplier.

We will finish with a final word about fire detection and control systems. Under British, and most other national regulations, fire detection and control circuits, plus emergency lighting and exit signage must use special fire survival cable made of a mineral-based insulation rather than the traditional thermoplastic of
data cables. The reasons are obvious as these critical circuits must survive at least thirty minutes of a fire situation and still do their job.

Where fire control systems are terminated in a controller, and the site is large enough to support multiple controllers (or the controller needs to interface with a BMS system) then at these points the cabling can be normal LAN grade, but hopefully of the low flammability, zero halogen or plenum style for higher safety levels in these critical areas.
Bookmark and Share
Home I Editor's Blog I News by Zone I News by Date I News by Category I Special Reports I Directory I Events I Advertise I Submit Your News I About Us I Guides
   © 2012
Netgains Logo