A Procurement Guide: Specifying HV/MV Cable Design Services

Every year, transmission operators and EPC contractors lose weeks — sometimes months — to cable design revisions that surface only after tendering has closed. A route that looked clear on paper crosses a protected watercourse. The conductor size was based on outdated soil resistivity data. A substation interface wasn't coordinated with the wider network study. These are not isolated errors, but the expected consequence of defining HV/MV cable design work services in the absence of a clear procurement process. 

For utility companies, renewable energy developers, and engineering managers responsible for issuing design scopes, the real risk isn't technical complexity — it's ambiguity in the brief. This guide sets out a practical, standards-based approach to specifying high-voltage cable design and medium-voltage cable design work, so procurement teams can compare proposals fairly and avoid the rework that erodes project margins. 

Why Cable Design Scoping Goes Wrong 

A large proportion of disagreements between clients and consultants can be attributed to three gaps in the initial brief: 

• Undefined boundary conditions. Ground temperature, thermal resistivity, and installation depth are often assumed rather than specified, leading to undersized or over-engineered cables. 

• Vague deliverable lists. "Provide cable design" means little without naming the calculation reports, drawings, and datasheets expected at each project stage. 

• No reference to governing standards. In the absence of IEC, IEEE, or BS EN requirements stated initially, consultants will simply revert to their own defaults, which may not be aligned with what your regulator wants. 
  

Addressing these gaps during the tender stage, rather than after the contract is awarded, is the most effective way for procurement teams to control project cost and schedule certainty. 

What "Good" Looks Like in a Cable Design Scope 

1. Clear Scope Boundaries 

A properly written brief will clearly define interfaces for cable sizing and selection, cable routing design, and high-voltage substation design. This will avoid the common problem of an engineer considering routing as somebody else’s responsibility and producing a sizing report that cannot be installed as shown. 

At minimum, the scope should specify: 

• Voltage class and system configuration (radial, ring, or interconnected) 

• Any preferences on conductor material and insulating type 

• Route corridor constraints (existing utilities, environmental designations, third-party land) 

• Interface points with substations, switchgear, or renewable generation assets 

• Required software or calculation methods (e.g., IEC 60287 for current ratings) 
  

2. Standards and Compliance References 

Reliable HV cable engineering service providers will work to internationally accepted standards, and these should be specified in your scope of work rather than being left to interpretation. Common references include: 

• IEC 60287 — Calculation of the current rating of cables 

• IEC 60840 / IEC 62067 — Design and testing of HV cables up to 500 kV 

• IEEE 575 — Bonding and shielding of cable systems 

• BS EN 50110 — Operational safety of electrical installations 

  
  

Listing to the relevant standards in the request proposal ensures that every bidder uses the same technical baseline. This makes it much easier to compare bids fairly. 

3. Deliverables Tied to Project Stages 

Cable design is not a one-shot output. It evolves through the stages of feasibility, FEED, and detailed design. A robust scope ties deliverables to each phase: preliminary route options and indicative sizing at feasibility, thermal and fault-level calculations at FEED, and fully coordinated installation drawings, bonding diagrams and as-built documentation at detailed design. 

Sizing and Selection: What Procurement Teams Should Ask For 

Cable sizing and selection are where technical assumptions have the biggest effect on costs. If cables are oversized, it wastes money. If they are undersized, there is a risk of thermal failure or early ageing of the insulation. When reviewing a consultant's proposed method, ask them to confirm: 

• The soil thermal resistivity used, whether from site tests or estimates based on desk studies 

• Cable grouping derating factors for the same number of circuits in common trenches or ducts 

• Capacity rules for growth and contingency matching your network planning horizon 

• Short-circuit withstand and fault current assumptions 

If a consultant cannot answer these questions clearly at the proposal stage, they are unlikely to provide a reliable design later. 

Routing: Beyond the Shortest Path 

Cable routing design is often seen as a formality, but it is usually the biggest source of project risk. Today, best practice is to use GIS-based corridor analysis together with environmental, geotechnical, and stakeholder constraints from the start, instead of routing first and consulting stakeholders later. 

For renewable energy projects that have offshore or remote onshore facilities, choosing the right route can make a big difference to the time required to connect to the grid. When this is necessary, early engagement with the network operator over the preferred corridors can make the difference of several months. 

Comparison: In-House vs. Specialist Consultant Delivery 

Criteria	In-House Team	Specialist Cable Design Consultant
Standards currency (IEC, IEEE, BS EN)	Variable, depends on training cycle	Continuously updated across projects
Software and modelling tools	Often limited to one platform	Access to multiple validated tools
Route/substation interface coordination	Requires cross-department handoff	Integrated within a single scope
Speed on multi-site/rollout programmes	Constrained by headcount	Scalable to programme size
Cost transparency for tendering	Internal cost allocation, less visible	Fixed-scope, comparable across bids

Neither model is always superior to the other. It all depends on the size of the program, internal expertise, and frequency of HV/MV design requirements for your company. The hybrid model is popular among many transmission companies and industries, which have internal control over strategic issues while bringing in an expert in cable design from the UK or regionally. 

A Procurement Checklist Before You Issue the RFP 

Prior to issuing a call for proposals, make sure the brief covers: 

• Defined voltage class, load profile, and growth assumptions 

• Named standards (IEC, IEEE, BS EN) the design must comply with 

• Stage-gated deliverables, not a single lumpsum "design report" 

• Site data availability (soil resistivity, geotechnical, environmental surveys) 

• Interface responsibilities between cable design and HV substation design teams 

• Evaluation criteria that weigh technical methodology, not just price 

  
  

  

  
  

Conclusion 

An accurate description of HV/MV cable design services does not involve jargon but requires accuracy in describing the scope. Defining the voltage class, standards, deliverables, and the site details at the outset ensure that the bids are objectively evaluated based on their true technical content rather than guesswork, avoiding the need for costly redesigns in the process. 

If you're preparing a tender for high-voltage or medium-voltage cable design and want a second opinion on your scope before it goes to market, VSS Power's engineering team can help you build a brief that gets accurate, comparable proposals from the outset. 

 

5 Key Takeaways 

1. Most issues regarding cable design are related to scope, not technology. Clearly define the scope and deliverables at the outset. 

2. Always mention IEC, IEEE, and BS EN standards in every RFP to make sure bids can be compared technically. 

3. The choice and design of cables depend on soil thermal resistance, derating, and fault levels. Ask the consultant to clearly state these criteria at the outset of the project. 

4. Cable routing design should include environmental and stakeholder constraints from the beginning, not as an afterthought. 

5. Employing a multi-stage deliverable process, including feasibility, FEED and detailed design, allows the procurement team to much more control over cost and schedule compared to a one-off cable design report. 
   

FAQs 

1. What standards govern HV/MV cable design?  

Important references are IEC 60287 on calculating ratings, IEC 60840/62067 on design and testing of HV cables, IEEE 575 on bonding and shielding and BS EN 50110 on operational safety. 

2. How is cable size determined for HV/MV projects?  

The sizing is decided based on load current, soil thermal resistivity, installation depth, grouping/derating factors, and short-circuit withstand requirements, and it is usually made in accordance with the IEC 60287 methodology. 

3. What's the difference between HV and MV cable design?  

The distinction between them is that HV cable design is used when the voltage level is above 66 kV. This type of design requires more attention to insulation and jointing. In addition, additional tests are required. 

4. Why does cable routing design affect project timelines?  

Poor routing choices typically surface as late-stage consenting challenges, third-party land negotiations, or conflicts with existing utilities – all of which can push out construction more so than redesign itself. 

5. Should I use an in-house team or a specialist in cable design consultant?  

This decision depends on the programme scale and the organisation's internal capabilities. Sometimes organisations decide to hire both.