A guide to Overhead Cable Management Systems

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Guide to Overhead Cable Management Systems


We have developed a guide to help identify which Cable Management Solutions you require


What factors determine system selection?

1) Location - internal or externa

2) Function - protection & support

3) Services - power only / power & data / ancillary

4) Material and finish - steel / stainless steel / other

5) Choice and cost


What factors determine system selection? 


Location 

Ceiling void 

•Services installed within a ceiling void ….not visible and only accessible by ….removing the ceiling tiles


Open ceiling 

• Services in open view -not hidden above …suspended ceilings


External 

•External services to and from buildings, …external equipment, plant rooms etc


Function

Protect

The installation method must provide protection against expected external influences e.g., trunking requires an IP or IK classification and support systems may need covers


Support

The system must provide support for all the services it will be carrying


Service

Data

Power

Ancillary


Metal and finish

Cable management systems are invariably exposed to atmospheric corrosion. The environment in which the product is installed is often the main criteria in the choice of material, finish, or surface treatment.


The most common finishes are: 

• Hot Dip Galvanizing (HDG) 

• Deep Galvanizing 

• Pre-galvanized (PG) 

• Stainless Steel 

• Electroplating with zinc


Choice and cost

Choice - there may not be any definitive ‘right answers’ for many cable management installations, it can come down to personal choice -however in specifying the most appropriate system it is all about asking the right questions.

appropriate system it is all about asking the right questions.


Cost-In simple terms, the more steel required to manufacture a cable management system, the more expensive it is. 

However, assessing cost should also include other factors: installation time; skilled labour; future proofing; recyclability; waste; longevity.


To support or protect

Support Section  

- Ladder systems Section 

-Tray systems Section  

- Wire mesh systems


Protect

-Trunking systems


Cable ladder systems (support)

Mainly used for supporting armoured power and control cables both indoor and outdoor. Used from small, strong installations to large scale heavy duty cable distribution where a structure is provided for mounting cable ladder. Cables must be fixed to ladder via ties or clamps 


Cables must be safe to touch


When specifying cable ladder systems consider:

• system that caters for differing loads from light duty (typically 50mm) through to extra heavy duty (typically 150mm)

• slotted rail design which allows components to be coupled together without the need for drilling

• system that includes adjustable bends

• system that includes time saving installation methods, therefore reducing installation time and fewer components for improved assembly time


• Cable ladder fittings are factory fabricated items to facilitate a change of direction and / or width such as : •Flat bend •Inside or outside riser •Equal or unequal tee •4 way crossover •Reducer

• Reducer

• Ancillary items are also available such as : 

• Adjustable connectors 

• Articulated risers 

• Dividers 

• Cantilever arms

• A full range of ladder covers are also available in both closed and ventilated options


Cable tray systems (support)

Used from small, strong installations to large scale heavy duty cable distribution where a structure is provided for mounting cable tray 

Cables must be fixed to tray with cable ties Cables must be safe to touch


When specifying cable tray systems consider:

• system that caters for differing loads from light duty (typically 12mm) through to extra heavy duty (typically 80mm)

• system with integrated slot pattern design that 

• system with integrated slot pattern design that provide installers with total flexibility without the need for additional drilling

• system that can uses a flexible connection system

• system that includes adjustable bends

• simple and versatile solution that aids on-site fabrication



Cable tray fittings are factory fabricated items to facilitate a change of direction and / or width such as: 

• Flat bend 

• Inside or outside riser 

• Equal or unequal tee 

• 4 way crossover 

• Reducer

• Ancillary items are also available such as : 

• Adjustable connectors 

• Articulated risers 

• Dividers 

• Cantilever arms

• A full range of covers are also available in both closed and ventilated options


Wire mesh systems (support)

Wire mesh used mainly for data cables but can also be used for small to large scale power distribution. Some systems can be a totally clip together solution. Wire mesh is highly versatile with fittings made on site.

Cables must be fixed to wire mesh trays with ties

Cables must be safe to touch


When specifying wire mesh / wire cable systems consider:

• system that caters for differing loads from light duty (typically 30mm) through to heavy duty (typically 100mm)

• a system that can be easily and quickly secured together with a clip solution, therefore not requiring nuts and bolts

• system with integrated range of wall and ceiling supports


Wire mesh fittings such as bends, tee’s, 4ways, reducers, inside and outside risers etc., are all made on site making this system very versatile, quick to install and cost effective

• Ancillary items are also available such as  connectors, dividers, cantilever arms, trapeze hangers, overhead hangers, brackets and clamps

• Some manufacturers offer a range of quick fix brackets and clips which can save up to 80% on installation times


Trunking systems (protection)

Cable trunking provides mechanical protection for cables, protection in public areas, electrical separation. Cable trunking is defined as a closed enclosure, of which one side is removable or hinged, used for the protection of cables

BS7671 2008 amendment 1 Section 521.10.1 includes the following statement for new installations : “Non-sheathed cables are permitted if the cable trunkin gsystem provides at least the degree of protection IPXXD or IP4X, and if the cover can only be removed by means of a tool or deliberate action.”


Lighting trunking Mainly used for lighting circuits, with clip-on steel or PVC lids. Often suspended from the ceiling via drops of threaded rod, lighting fittings commonly attached directly to the trunking system via suspension units

Systems normally have their own range of accessories including bends, tee’s, 4-ways, couplers, stirrup hangers and brackets etc


When specifying distribution trunking systems consider:

• trunking system that caters for differing loads, sizes and compartments 

• integrated coupling system for ease of connection and reduction of installation time 

• safety edge to reduce potential of cable snagging and promote safer handling 

• clip on lid system with integrated turnbuckle 

• shake proof screws that reduce potential screw loss and ‘materials falling from height’ issues 

• ensure an integrated system were all fittings and accessories work together 

• adherence to standards such as IP4X


Trunking fittings such as bends & tee’s are available in different angles and lid arrangements. There are also special application fittings such as double depth tee’s and 4-ways

• Accessories include stop ends, flange couplers, reducers, bell mouth fittings, change face units and socket outlet plates

• Ancillary items include earth links, cable retainers, stirrup hangers, pin racks, grommet strip and spares like additional screws.


Design & specification guidance

Ladder and tray design factor 12-point summary:


1) Distributed loads 

2) Point loads 

3) Imposed load (snow, wind and external ....forces) 4) Safety factor

4) Safety factor 

5) Deflection 

6) Spacing of supports & location of couplers 

7) Capacity 

8) Installation of cables within a support system 

9) Earth protection 

10) Segregation –Electro Magnetic ......Compatibility (EMC) 

11)Thermal expansion and contraction 

12) Flame propagation


Design & specification guidance

1) Distributed loads

• Distributed loads –if full details of the cabling layout are known, the load can be calculated using the manufacturers published information such as product weights, loading graphs, and cable manufacturer’s details ie: cable weights and diameters

weights and diameters

• If data is not available , then a calculation may be based upon: cable laying area (m2) x 2800 (where cable laying area = w(m) x h(m))

• It is good practice to allow both the physical space and sufficient load carrying capacity for the future addition of 25% more cables


2) Point loads

• Point loads –consist of bunched cables or permanent equipment such as lighting luminaries & should ideally be positioned as close to supports and side rails as possible

• The effect of a point load is quite complex so a  simple alternative approach is available simple alternative approach is available 

• assume the point load will be situated in worst position at mid-span. The force this imposes can be taken as equivalent to twice that imposed by a uniformly distributed load. 

• thus the point loads can be converted to the equivalent UDL’s and added to other UDL’s to give a total uniform load


3) Imposed loads

• Imposed loads –Manufacturers loading graphs don’t take into account external forces such as snow, wind and ice. Therefore, if installed outdoors, these must also be taken into account at the design stage the design stage

• Any extra weight should be added to the total cable weight and cross referenced with the manufacturer loading graphs

• Appropriate design data for UK weather conditions are given in BS EN 1991-1-4 : 2005 and  BS EN 1991-1-3 : 2003 Eurocode1


4) Safety factor

• Safety Factor –Manufacturers safe working load graphs should have a safety factor built-in

• This would normally be the load before failure divided by a factor of 1.7 minimum

• A designer may need to increase this safety factor 

• A designer may need to increase this safety factor depending upon the circumstances. If the system is going to be subject to aggressive abuse a safety factor as high as three or more may be used

• Care should always be taken not to over-design the system by using too high a safety factor


Material selection

When planning any cabling or support installation the choice of an appropriate corrosion resistant material and finish is always a key issue at the specification stage, especially for more challenging environments


Chemical corrosion

• Atmospheric pollutions are present in most  situations where cable support systems are to be installed, thus mild chemical corrosion is normal

• Systems installed in areas of higher 

• Systems installed in areas of higher concentrations of chemicals must receive more consideration to select a finish which provides the best combination of initial cost and life expectancy

• Some manufacturers publish tables giving guidance on the suitability of standard materials and finishes


Electro-chemical corrosion

Steel rivet

Stainless steel

Corrosion

• When two dissimilar metals are in contact and become damp it is possible for corrosion to be induced in one of the metals •may progress rapidly •cause considerable damage

• Electrochemical (alternatively referred to as electrolytic or bimetallic) corrosion takes place because: •the metals behave as electrodes •the moisture acts as an electrolyte causing corrosion

• The likely effects of this reaction can be predicted using the Galvanic Series


Material selection -selecting the right finish

• Pre-galvanized to BS EN 10327 : 2004 grade DX51D - Continuously hot-dip zinc coated low carbon steel

• Post galvanized to BS EN ISO 1461 : 2009 - Hot dip galvanized coatings on fabricated iron and steel articles

• Deep galvanizedhigh silicon steel to BS EN 10025-5 grade ……..S355JOWP - Steels with improved atmospheric corrosion resistance

• Steels with improved atmospheric corrosion resistance

• Stainless stee lto BS EN 10088-2 –AISI 304L and AISI 316L - Pickle and passivation for stainless steels in contact with foodstuff

• Electroplated zinc to BS EN ISO 2081 : 2008 - Electroplated coatings of zinc with supplementary treatments on iron or steel

• Dacromet®a zinc and aluminium coating, equivalent to Post Galv - used on small accessories and fixings, which are difficult to hot dip galvanize


Summary

• The location and requirement to support / protect the overhead cable must be established from the beginning

• The nature of the supply and the cable routes need to be determined

• The clients’ requirements for the initial mounting position / location together with the type of cables to be installed need to be considered

• After the system has been selected, the size of the ladder, tray, mesh  

• After the system has been selected, the size of the ladder, tray, mesh or trunking which is to be used must then be determined

• Particular attention to be paid to the cable capacity, segregation and spacing requirements of the Wiring Regulations