11kV Cable Pulling – What Is The Maximum Distance For Ease of HV Cable Pulling Between Manholes
Published 14 Mar 2018
Uploaded By Chris Dodds – Thorne & Derrick Sales & Marketing Manager
In response to a question posed on Voltimum, the leading electrical industry portal, Nexans provided the following answer in reply about the maximum 11kV cable pulling distances between manholes when laying medium/high voltage power cables using cable socks.
T&D, the UK’s leading Cable Pulling & Laying Equipment Supplier, can provide expert technical recommendations and support for all cable pulling and laying projects into both open trench (directly buried) and cable duct.
Important procedural requirements apply to the installation of all MV-HV underground cable pulls irrespective of the method used.
Installation shall be carried out by experienced cable pulling teams with a thorough understanding of the risks specific to the installation methods being used. The installation design, cable pulling equipment and techniques shall be designed to:-
- Minimise cable pulling forces on MV-HV cables
- Cause no damage to MV-HV cable sheaths during handling/installation into duct or trench
Often cables are snagged or damaged by bedding or backfill materials during the the cable pull process on the cable trench bed – contact us to discuss cable sheath repair products.
Pictured : Manhole Cable Rollers – care must be taken during high voltage cable pulling not to exceed the maximum pulling force and tension to avoid 11kV cable damage. The cable rollers are designed for placing at the edge of the manhole or pit entrance to ease the cable into position.
Question: I’m installing a high voltage 11kV cable in PVC sleeves and I want to introduce manholes on the straight length of the HV power cable route. What will be the maximum distance you would recommend for ease of high voltage cable pulling of the 11kV cable from one manhole to the other?
Answer: This can only be answered properly on a case-to-case basis as it depends a lot on the topography and direction of the proposed 11kV cable pulling route.
This is especially so in urban areas where many bends may be necessary to avoid underground utility cables and pipes such as like sewers, water and gas. If there are no bends, we have still must consider the friction coefficient of the particular cable duct with the 11kV cable.
Of course, cable lubricants can be used as long as they do not harm the sheath material or the duct material – lubrication of the 11kV will reduce the co-efficient of friction of the cable pull between the 11kV cable sheath and inner cable duct wall.
If we speak about 11kV triplex cables, you will get them only in smaller lengths because of the diameter – I suppose 350m on a perfectly straight line shouldn’t be a problem.
But please take into consideration the maximum pulling force, which is: 30N/mm2 of conductor cross-section for aluminium conductors and 50N/mm2 of conductor cross-section for copper conductors.
Going above these forces can damage the 11kV cables and maximum cable pulling vary according to the specification of the medium/high voltage cable.
Maximum Cable Pulling Tensions
High Voltage Cables Up To 33kV
Maximum permissible pulling tensions for each 11kV/33kV cable type are given below.
These cable pulling tensions must not be exceeded under any circumstances. Efforts should always be made by the cable pulling teams to achieve lower figures by careful setting out of the work and positioning of the MV-HV cable drum.
|Maximum Cable Pulling Tensions LV 11kV 33kV Cables (kN)|
|Conductor Size (sqmm)||95sqmm||150sqmm||185sqmm||240sqmm||300sqmm Al||300sqmm Cu||500sqmm||630sqmm|
|11kV 1 Core XLPE||2.85||–||5.55||–||9.0||15.0||–||31.5|
|11kV 3 Core XLPE||3.91||–||6.36||–||9.79||–||–||–|
|33kV 1 Core XLPE||–||5.5||–||–||–||–||14.6||18.0|
♦ Info: Scottish Power Energy Networks, CAB-15-003: Handling & Installing Cables Up To 33kV
Risk Of Arc Flash & Safe Digging
Civil engineering contractors, jointers and pulling teams must be aware of the arc flash dangers associated with utility excavations when working around buried services including electricity cables. Attention is drawn to the requirements and recommendations contained in Health and Safety Executive guidance notes HSG47 “Avoiding Danger from Underground Services” and HSG185 “Health and Safety in Excavations”. UK DNO’s publish guideline documents about “Safe Digging” and these can be consulted online.
High Voltage Cable Pulling
Calvi Electric Company uses Southwire A-Frame truck to facilitate a 1300′ high voltage cable pull through a manhole system. During the video you will observe the high voltage cable being taken up in sections. At the other end of the cable pull a Greenlee Ultra Tugger set up is located, the average for this cable pull was 6 ft per second.
The reason for the sporadic uptake was variable stretch and tension being placed on the cable pulling rope. The total length of the HV cable pull was 1270′. The utility learned that with the ease at which the Southwire A-Frame trucks payoff that it was not necessary to have this large of a crew to handle the consolidation of cable into the trunk of the cable pull. Once set up this cable pull could have been performed with 4 crew members. Additional crew members were necessary and productive in initial manhole set-up, reel set-up and attending to manholes where the wire was being pulled straight through.
Sealing Cable ducts
Where electricity, pilot and telephone cables are installed into electricity cable ducts the utility engineering standard would normally recommend all cable ducts entering substations and buildings to be duct sealed to prevent the ingress of water and gas – this also applies to 33kV, 66kV and 132kV high voltage substation cables where cable transits are required.
Cable Pulling & Cable Laying Equipment Suppliers & Distributors
Thorne & Derrick International distribute the most extensive range of Cable Pulling & Cable Laying Equipment to enable the installation of low, medium and high voltage power cables into underground trench or duct – products also supplied for fibre optic blowing, subsea trenching, offshore umbilical installations and pulling armoured cables onto cable tray.
More Cable Pulling Blogs
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- Cable Laying & Pulling – Installing LV-HV Cables Into Duct
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