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The Use of SCS in Intelligent Buildings


Intelligent Building Systems (IBS) is Lucent's extension (or subset) of the Structured Connectivity Solution (SCS) to include Fire, Security, Lighting HVAC and Energy Management systems. In fact, IBS is continually being developed to include as much of the building environment systems as possible. There is a continuing debate whether the I should stand for Intelligent, or perhaps Integrated, which probably describes more accurately what the IBS actually does, i.e. provides a common platform for environmental systems to communicate.

This document aims to aid those who are already familiar with Lucents SCS, to extend SCS design to include for building environment systems as well as the familiar Data/Voice applications. In addition, the document will mainly address the connection of Honeywell specific controls equipment to the IBS. It is imperative that a fully trained SCS engineer (i.e. one who has completed both the Installation & Maintenance course and the Design & Engineering course) work closely with the BMS/lighting/fire and security engineers in order to both educate on the best use of the structured cabling, and also to be educated on the requirements of specific equipment. Issues that need to be discussed early are the density and spacing of points, bus length capabilities and power requirements.

Although the building structure itself may commonly have a life cycle of 60 years or more, the data systems have life cycles of the order of 3 years. Digital voice and video systems have life cycles of 5 - 7 years and Building Management Systems (BMS) 7 - 14 years. Traditionally, as systems are upgraded, the proprietory cabling for each system is ripped out and installed for the next system. Systems are often only guaranteed with specific cable types. The advantage is evident for an open cabling system that can remain in place for 20 years, still covered by an applications and parts warranty, having seen up to six data system changes, three voice system changes and a couple of BMS changes

An open cabling system has existed for years in the data/voice world and gives the customer greater freedom to mix and match data systems without feeling tied in to a specific system provider. The same thing is now beginning to happen in the building systems world as more and more system manufacturers design their systems to operate across open structured cabling infrastructures.

Although many technological barriers have been overcome in integrating these different systems, local codes such as local fire regulations may prohibit the use of certain types of UTP.

What IBS does not do is integrate these building systems on a software/front end presentation level. This software level of integration is another stage in the bringing together of these systems, even common standards such as the Echelon Bus are not yet 'common' enough for different manufacturer's equipment to communicate with one another. This is due to the fact that individual manufacturers tweak the chips which implement the Echelon standards so preventing interoperability. A parallel in the data world is 10BaseT ethernet devices from one manufacturer talking to 10BaseT devices from another manufacturer.

So why use a SCS for building systems?

  • It reduces the cost to install the cabling.
  • One specialist cabling contractor can install all the cabling for all systems, leaving the system specialists to concentrate on their systems, therefore less time for them on site.
  • The time to install the actual cabling is less.
  • Commissioning the systems is quicker as the cabling system has already been 100% tested according to the high standards normal in the data world.
  • Improves flexibility in adding, moving and changing environmental systems.

General IBS Design

IBS is effectively SCS for control systems and the design considerations are almost identical to those of the standard SCS. The following sub-systems exist in IBS:
  • Campus Backbone Sub-system.
  • Riser Backbone Sub-system.
  • Equipment Sub-system - The key here is to centralise the control devices as much as possible in order to minimise the number of custom control panels that often have to be made.
  • Horizontal Sub-system.
  • Coverage Area Sub-system - This is used to describe the equivalent of the Work Area Sub-subsystem and typically has a wider area to consider.
  • Administration Sub-system - Cheaper jumper wire can be used for patching, since the data speeds are very low and crosstalk is not a problem.


Coverage Area

The Coverage Area topology can be quite different from the normal Work Area topology, in that, devices can be looped or chained according to the particular system requirements. The Information Outlets (I/O) are typically mounted in places such as walls, ceiling voids and pillars as well as floor voids.

Extended Coverage Area wiring is appropriate for devices that are designed to be connected in a bus or loop topology. Rather than having individual outlets for each device, devices can be chained together from one outlet, or looped together between outlets. In addition, fault tolerant device wiring is required for immediate detection of an open cable in a loop for instance.

The size of coverage area varies depending on the type of environment. Experience has shown that the following are reasonable guidelines:
  • Office Areas - 25 sq. m (7-9 i/os per area, 3 for HVAC, 4 for security, 2 for lighting etc.).
  • Factory, parking areas - 46 sq. m (4 i/os per area).
  • Hotel - 5 i/os per room (fire, security, hvac).
  • Plant room - blocks of outlets concentrated near AHUs (12 to 24 i/os per AHU),or associated MCC equipment. Honeywell's 'Remote I/O' product for the XL10 controller allows I/Os to be located remote from the controller and locally to the plant. This way less cable is needed as the Remote I/O device communicates to the XL10 via the bus.

This compares with a typical office area of 9 sq. m with 4 i/os per work location.

The precise density of outlets would need to be carefully considered and a balance struck between over-stocking on outlets that are never used and under-stocking so that ceiling tiles have to come down and new cable runs installed when extra security doors are installed, for example. In addition, control devices may be required under the floor e.g. wet systems. When tendering, careful consideration needs to be made of both the current and possible future requirements of the occupier with regards to the environmental management. What you are aiming for is a cabling infrastructure that minimises future disruption of additional cabling installation, and flexibility such that the occupier can swap and change around devices, much as they can with data/voice equipment. Remember that a number of devices can hang off one socket (see later), it is important to work with the controls manufacturer to at least understand the communications topology of their equipment. An example, is a customer who may make great use of perimeter heating and automatically controlled blinds or window openers. In this instance, you will probably find that increasing the density of outlets near the edge of a floorspace is wise, after all this is what we have done for years in the data/voice environment.

There are five main types of device signals used in control systems:
  • Analogue Input (AI) - typically a 4 to 20mA current loop signal used to provide information from remote devices such as temperature sensors to controllers.
  • Analogue Output (AO) - typically a 4 to 20mA signal supplied by the controller to control a remote device such as a valve or damper actuator.
  • Digital Input (DI) - this is normally a binary signal supplied by an open/close contact on a differential pressure switch located across water flow pumps, for example.
  • Digital Output (DO) - a digital pulse from the controller to signal on/off or open/close to remote devices. Normally via interposed relays which then allow through or shut off power to devices.
  • Control Bus - between controllers and front end computers.
For circuits where a maximum circuit resistance is important, the following table can be used as a guide.

Circuit Resistance (ohms) Cable run (m)
10 53
20 106
30 160
40 213
50 266
60 320
70 373
80 426
90 480
100 533

This table is based on the fact that the cable is 1061 (or equivalent) which contains solid core 24AWG wires, two of which are used across a device. The resistance of this cable is 9.4 ohms per 100m. The distance in the table is the cable distance not the circuit distance, the circuit distance being to the device and back!

The following table is useful when connecting devices that require significant current and a minimum operating voltage (based on 24v primary supply voltage):

Circuit Current 50% drop i.e. 12v at device 25% drop i.e. 18v at device 10% drop i.e. 21.6v at device 5% drop i.e. 22.8v at device
Current (mA) Max. distance (m) Max. distance (m) Max. distance (m) Max. distance (m)
10 6401 3219 1288 643
20 3219 1609 643 322
30 2146 1073 429 215
40 1609 805 322 161
50 1286 643 258 129
60 1073 536 215 107
70 920 456 182 91
80 792 402 161 80
90 701 354 139 69
100 643 320 129 64
200 322 160 64 32
500 129 64 26 13
1000 64 32 13 6

Highlighted in the above tables is a 50ohm device which is typical of a BMS device. This unit is fine up to 258m on the SCS.

The following formula can be used to give the maximum cable distance allowed:

Distance = [V x v] / [100 x I x r]


Distance = Max. cable distance (m).
V = Voltage of device (v).
v = volt drop (%).
I = Current (Amps).
r = resistance of cable per m (ohms), in the case of 1061C, this has the value 0.188.

Again, this cable distance is assuming a two-wire circuit.

For an example, you may wish to work out the maximum distance allowed for a 1061 cable running to a door solenoid which has been selected to draw 375 mA, supplied by a power supply giving 24v and a maximum voltage drop allowed of 10%. Using the above formula:

Distance (m) = [24 x 10] / [100 x 0.375 x 0.188] = 34m

Therefore, the cable run must not exceed 34m.

The design guidelines suggest that a maximum of one amp per conductor is allowed (although this will not get you very far!). If there are a number of devices connected via one four pair cable then the following table gives a guide for the maximum current allowed per cable:

No. of pairs Max. current in wire (A) Current (A) per pair Current (A) per cable Max. Fusing (A)
1 1 2 2 1.5
2 0.825 1.65 3.3 1
3 0.55 1.1 3.3 0.75
4 0.4125 0.825 3.3 0.5

Doubling up of conductors is permissible, but only for non-Fire systems, and then only for increasing the signal transmission distances NOT the power capacity of the cable. There is always the possibility of a break in one of the conductors, therefore putting more load on the remaining conductors.

For audio voltage, the cable limitation is 70V RMS and the current 1Amp RMS.

Traditionally, controls devices present screw terminals for the connecting wire. However, these terminals are designed for 16-18 AWG cable and are not suitable for the smaller 24AWG 1061C cable. Before connecting the 24AWG cable, you need to crimp pins or spade lugs to the ends of the wires to give the screw terminals a more resilient connection. The more forward thinking controls manufacturers are now providing 110 blocks or RJ45 sockets as part of the end device. There is always the option of adding such connections yourself, certainly at the controller end, where there is often a custom panel made which can provide space for 110 blocks/RJ45 sockets within the design of the panel itself.

Horizontal Sub-system

The total cable distance allowed is 100m. This is made up of 80m (as opposed to 90m in the data/voice environment) for the frame to outlet run, 14m for the flylead connection from the outlet to the end device(s) and 6m for the patch cable.

Determination of which closets the controllers are located is dependent on the particular device protocol or voltage drop distance limitations. Certain devices, such as the 50ohm example above, may be fine across a couple of cross connects and the riser sub-system, provided the distance does not exceed 258m.

When chaining devices (as in the above diagram) keep to 5 devices or less off a single i/o, off a single pair. These 5 devices may be in the same Coverage Area or in adjacent Coverage Areas. Devices may be chained off one pair, or you could use another pair to connect another device, obviously, for a four pair cable you are limited to 4 chained devices when using this method. There is no reason why you could not use 25 pair cables to satellite 110 frames for further distribution.

Standard rules apply when running the UTP cables near power cables. This is important if UTP wiring is being installed in plant rooms where alot of high-voltage switching is likely to be happening. Generally, the UTP cable will need to be on tray and metal trunking within the plant room environment. There are no problems in sharing the tray with other cables provided they are not medium or high power cables. An example, is sharing runs with Fire cables.

Although different devices can share the same 4-pair cable, these devices have to be part of the same system. Different systems (e.g. data and security) must use separate cables.

In Plant rooms, multi-socket boxes can be used to provide concentration points for Air Handling Units (AHU) to connect to using double ended RJ45 cables. This then allows the installation of extra capacity from the MCC panel to the area near the AHU. The occupier may wish to replace the controls after 7 years with newer technology that may require more inputs/outputs. There may be (always will be, actually!) changes of requirements both during installation and early occupation, and extra control may be required. Plugging extra sensors into localised sockets is far easier than running extra cables around a live plant room!

A common requirement nowadays is for CCTV. CCTV uses a baseband signal (< 10MHz) and is more than capable of running down Category 5 UTP. There is however, some caveats; one is that you need to examine carefully the specification of the security system. Telemetry signals (for motor control of the camera) can either be sent down the same pair as the video signal (in which case distances can be limited to less than 100m using the baseband video baluns), or the telemetry signals could be sent down a separate pair (thereby allowing greater distances across cross-connects, perhaps up to 250m).

Whether you are in a pre or post-tender situation, it is a good idea to provide a small test rig (e.g. a box of 1061C, a 100 block and a bank of RJ45's correctly terminated) for any equipment manufacturer to test their equipment. This is especially useful for testing how far buses can operate reliably, or CCTV signals with/or without telemetry. Issues can then be resolved before installation, and design changes can occur on paper and not on site!

Riser Sub-system

Sizing of the riser cables is based on the number of pairs being used between closets and the number of pairs likely to be used by devices that are patched across a number of closets, e.g. a temperature sensor. Building systems must be kept in separate binder groups from the data/voice systems and each other, i.e. BMS systems need to be in a different binder group from Security systems. In addition, video systems must be kept in separate sheaths from everything else due to the sensitivity and high speeds of the video signals.

Administration Sub-system

At least one Telecommunications Closet (TC) is required for every 900m^2 of office space according to the EIA/TIA.

The following patching can be carried out at the frame for 'Supervised' devices that require an End of Line Resistor for detection of disconnections. The devices are 'chained' together, either individually or on a per socket level, or a chain of devices off one socket.


Unsupervised circuits can be bridged (multi-dropped or T-tapped). This can be done at the outlet end using a 367A Bridging Adapter that provides 8 x RJ45 jacks that have each wire bridged from the original outlet across all the corresponding pins of the RJ45s. The bridging could also be carried out on the frame as detailed in the following diagram:


Equipment Sub-system

The Equipment can be BMS controllers, lighting controllers, bus repeaters, security controllers, Graphic Front End systems etc. Communication Bus distances can vary from 150m to 1200m depending on the manufacturer's specifications, and often repeaters can be inserted within the bus circuit as it comes back to the frame and goes out again (e.g. Echelon bus repeaters for the Honeywell XL10 product).

Spade lugs and pins may still be required to connect jumper wire from the equipment field to the controller cards, although it may be prudent to design controller panels with IDC 110 blocks instead of DIN rails. This would require a culture change with the panel manufacturers, however it would make site installation much less fiddly. Ideally, controllers should have RJ45s, or at the very least 110 blocks on the chassis for ease of connection in the field.

Front End equipment often runs on Ethernet LANs so making the job of distributing management much easier than in the past. The data/voice systems can distribute the management stations.

The following tables give ideas on the uses of the cable pairs:


Wire W-Bl Bl W-O O W-G G W-Br Br
RJ45 Pin 5 4 1 2 3 6 7 8
Bus +S -S            
Analogue-In S G            
4-20mA +24 S            
Analogue-Out S G            
Power             AC AC
Digital-In S1 G1 S2 G2        
Digital-Out S1 G1 S2 G2        

Security and Access Control:

Wire W-Bl Bl W-O O W-G G W-Br Br
RJ45 Pin 5 4 1 2 3 6 7 8
Data 0 X              
Data 1   X            
LED     X          
+Power             X  
Ground               X
Door Strike Power         X      
Door Strike Common           X    

Honeywell Specific Requirements

The Peer bus is used by Excel+ controllers to communicate with one another. The C-Bus (Central Bus) is used by Excel 500, EMC controllers and IRC Multicontrollers. These buses use RS485 on 2 wires at 9.6Kb/s. The IRC controllers have a local Room bus (R-Bus) which uses a 3.5mA current loop on 25VAC (three wires; one for forward current and two for the return) and is not suitable for structured cabling. The old S-Bus (System Bus) is used to connect the old Excel Classic controllers and uses RS422 on 2 wires at 2.4Kb/s.

The S-Bus, C-Bus and Peer bus can be multidropped (T-tapped) and up to 29 devices can be supported on each of S-Bus and C-Bus types and 22 devices on the Peer bus. Using the 24AWG UTP, the bus distances have a maximum of 600m (exception being the C-Bus if a CSS is connected in which case the distance can be up to 800m). Up to two bus extenders can be used in each bus, each one extending the bus by 800m. The CSS now comes on a PC mounted board rather than the old method of an RS232 connection from CSS to PC, which could only run 15m on UTP.

If the S-bus/C-Bus is star wired, ie. multidropped at the frame, up to a maximum of 7 branches, then the maximum bus distance drops to 300m, unless a CSS is being used, in which case 400m is allowed. The restriction is that a maximum of 5 devices is allowed on each branch.

The following table shows bus loads and lengths for the Peer bus:

Max. bus length (m) Max. loads (devices)
152 22
304 15
457 13
609 11
914 7
1219 6

In a star configuration then the rules are that no more than 20 devices are allowed with no more than 6 on each branch, and the trunk length must be less than 152m whilst the branch lengths must be between 152m and 762m. The End of Line resistor configuration consists of two 62 ohm resistors each one bridging from each of the two wires to a common point. The EOLRs are attached at the extreme ends of the bus.

Generally, end sensor cable distances should be no more than 183m to minimise noise from outside sources.

How many devices, and how far cable runs can be, will depend on the individual manufacturers specifications. The standard SCS guidelines such as 80m maximum horizontal runs, and so forth, provide a basis for designing the generic structured cabling. It could be the case that some manufacturers will require to site certain equipment at every closet in order to minimise distance problems (such is the case with LAN equipment). In other cases, and particularly with lower data speeds, the equipment could be located more centrally such that some devices are linked across a number of cross connects.

Current Fire codes prevent the use of the SCS cabling in Fire systems other than backup monitoring, even the plenum rated cable is not sufficient. This may change in the next 5 years as consultants try to persuade the Fire authorities of the benfits of SCS systems and alternative designs that get round having to use mineral sheathed cables.

(The tables in this document were originally sourced from Avaya Technologies and are based on their SCS Systimax Product).

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