Trenching is the excavation of a narrow channel in the ground to install underground infrastructure—most commonly power cables, conduits/ducts, earthing conductors, and sometimes communications lines. In EV charging projects, trenching is a core civil works activity used to connect chargers to distribution boards, street cabinets, transformers, or grid connection points.
Trenching is especially common in on-street charging, car parks, fleet depots, and commercial sites where cable routes must cross paved areas.
Why Trenching Matters in EV Charging
Trenching is often one of the largest cost and disruption drivers in charger deployment. It matters because it:
– Determines installation time, site disruption, and permit complexity
– Drives a large share of CapEx (excavation, reinstatement, traffic management)
– Affects future scalability depending on whether spare duct capacity is installed
– Introduces risk (utility strikes, water ingress, settlement, poor reinstatement)
– Impacts accessibility and safety in public spaces (pedestrian routes, tactile paving)
Well-planned trenching can reduce total project cost and avoid repeat works.
What Trenching Typically Includes
A trenching scope usually covers:
– Route surveying and utility detection (avoid gas/water/fiber)
– Excavation to required depth and width (per local rules)
– Installation of ducts/conduits, cable protection, and marker tape
– Pull pits / chambers where needed for cable pulling and access
– Cable installation or cable pull preparation
– Backfill (often layered, with compaction requirements)
– Surface reinstatement (asphalt, concrete, paving stones) and curing
– Cleanup, as-builts, and inspection sign-off
Trenching in Different EV Charging Environments
– Car parks and private sites: simpler access, fewer permits, easier phasing
– On-street and public realm: strict street works permits, traffic management plans, and reinstatement standards
– Fleet depots: long runs and high-power feeders may require deeper/wider trenches and heavier duct banks
– Mixed-use developments: careful coordination with other utilities and stakeholder access needs
Key Design Considerations
– Cable sizing and voltage drop drive trench route and conductor selection
– Duct sizing and bend radius affect pullability and future upgrades
– Separation from other utilities and minimum cover depth requirements
– Water management and drainage to avoid duct flooding
– Future-proofing: install spare ducts and pull ropes for expansion
– Minimize crossings of sensitive areas (trees, crossings, tactile paving zones)
Cost Drivers and Constraints
Major trenching cost drivers include:
– Surface type (asphalt vs concrete vs stone paving)
– Depth/width requirements and ground conditions
– Traffic and pedestrian management requirements
– Utility congestion and need for rerouting
– Reinstatement quality requirements and warranty periods
– Out-of-hours work restrictions and permit fees
Common Pitfalls
– Underestimating reinstatement scope and local standards
– Skipping spare ducts, causing repeated excavation for future chargers
– Poor compaction leading to settlement and rework
– Incorrect duct routing or bend radius making cable pulls difficult
– Damaging existing utilities due to inadequate detection
– Blocking pedestrian routes or failing accessibility requirements during works
Best Practices
– Survey early and coordinate routes with all stakeholders
– Plan trenching phases to minimize disruption and total permit time
– Install spare duct capacity and label ducts for future expansion
– Use proper bedding, marker tape, and layered compaction
– Document as-builts (photos, measurements, duct layout) for long-term maintenance
– Align trenching with electrical works, cabinet installation, and reinstatement in one coordinated schedule
Related Glossary Terms
Street Works Permits
Traffic Management Plans
Surface Reinstatement
Spare Duct Capacity
Spare Conduit Routing
Pull Pits
Sub-distribution Boards (SDBs)
Transformer Upgrades
On-street Charging