GRP HV/LV Cabinets and DNO Enclosures
Bespoke GRP electrical enclosures for secure, long-lasting protection of critical power distribution equipment
SGI Composites designs and manufactures bespoke GRP enclosures for HV switchgear and associated equipment, LV cabinets and DNO enclosures. Manufactured in the UK, our composite housings support electricity distribution, infrastructure and industrial projects.
We work with Distribution Network Operators (DNOs), Independent Distribution Network Operators (IDNOs), Independent Connection Providers (ICPs), electrical contractors, consultants, switchgear manufacturers, utility companies, developers and industrial asset owners.
We design and manufacture the GRP enclosure around the approved electrical design, equipment layout, civil requirements and applicable DNO, IDNO or asset-owner specification. From compact metering cabinets to larger equipment housings, dimensions, access, ventilation and security can be tailored to the project.
What Are HV/LV Cabinets and DNO Enclosures?
HV and LV electrical enclosures provide protective housings for high-voltage and low-voltage equipment. Their design must accommodate the equipment, environmental conditions, cable routes and access needed throughout the installation’s life.
The requirements depend on who will own and operate the infrastructure:
- DNO/IDNO-adoptable infrastructure: Enclosures for equipment intended for network-operator adoption must satisfy the relevant operator’s specifications and project approval process.
- Privately owned electrical networks: Enclosures for customer-owned distribution equipment follow the approved electrical design and asset-owner requirements, alongside any applicable network-interface conditions.
- General industrial electrical enclosures: Housings for distribution, control, communications and other equipment are specified around their intended use, site conditions and applicable standards.
DNO or IDNO approval or acceptance must be obtained for the individual design and project. SGI enclosures are not automatically “DNO approved”.
GRP does not rust, making it well suited to coastal, roadside and industrial locations. The resin and finish can be specified around the expected exposure, helping reduce the need for corrosion treatment.
An appropriately specified external finish helps withstand rain and prolonged UV exposure. Weather resistance and ingress protection must be assessed against the complete enclosure design, including doors, ventilation and cable entries.
GRP is inherently non-conductive. Earthing and bonding requirements for equipment, metallic fittings and the complete installation must still be determined by the electrical designer.
GRP offers a high strength-to-weight ratio. Its comparatively low weight can simplify handling, transportation and installation, particularly where access or lifting capacity is restricted.
GRP does not rely on a painted metal surface for corrosion protection. This can reduce routine maintenance, while doors, seals, locks and ventilation components still require appropriate inspection.
GRP can be moulded and fabricated into project-specific forms, allowing custom dimensions, compartment layouts, access openings and internal mounting features to suit the installation.
GRP Cabinets for High- and Low-Voltage Equipment
Glass Reinforced Polymer (GRP) provides a durable, corrosion-resistant housing for electrical equipment in exposed locations. SGI manufactures enclosures around the approved equipment layout, allowing for mounting loads, heat losses, cable connections and operational clearances.
Depending on the project specification, our GRP electrical enclosures can accommodate:
- HV switchgear and ring-main units.
- LV switchboards and distribution equipment.
- DNO or IDNO intake and metering equipment.
- Transformers, where appropriate to the approved design.
- Protection and control systems.
- Cable termination and connection equipment.
- Communications and telemetry equipment.
Equipment selection, electrical design and installation requirements remain with the appointed electrical specialists. SGI’s role is to develop and manufacture the enclosure around those agreed requirements.
Built to Meet the Required Electrical Enclosure Specification
The correct specification depends on the equipment, location and organisation adopting, operating or maintaining the installation. For an initial technical review, please provide:
- Applicable DNO, IDNO, client or asset-owner specification.
- Equipment drawings and general arrangement drawings.
- Required enclosure dimensions and available site footprint.
- Equipment dimensions, weights and heat losses.
- Required installation, access and maintenance clearances.
- Cable-entry, trench, duct and gland-plate arrangements.
- Compartment segregation and locking requirements.
- Required IP and impact-protection ratings.
- Fire-performance requirements.
- Ventilation and condensation-control requirements.
- Plinth, foundation and fixing details.
- Delivery, lifting and installation restrictions.
- Environmental exposure, colour, finish and identification requirements.
Applicable Standards and Project Compliance
Applicable requirements are agreed for each project. These may include BS EN 60529 for IP ratings, BS EN IEC 62208 for empty LV switchgear and controlgear enclosures, and relevant parts of BS EN IEC 61439 where the enclosure forms part of an LV assembly such as BS EN IEC 61439-7:2023 for assemblies used in applications including EV charging stations or BS EN IEC 61439-8:2026 for assemblies used in photovoltaic installations. Relevant DNO G81 documents, IDNO requirements and project-specific specifications may also apply.
Compliance relates to the complete agreed enclosure design and specification, including openings, doors, ventilation, fixings and interfaces. GRP material properties alone do not establish compliance. Applicable editions, verification evidence and responsibilities must be agreed, with the assembly manufacturer responsible for compliance of the completed LV assembly.
Applications Across Energy, Utilities and Infrastructure
SGI Composites manufactures GRP enclosures for electricity distribution sites, privately owned networks and industrial installations. Each housing is configured around the equipment and the requirements of the organisation responsible for the asset.
Applications include renewable energy, battery storage infrastructure, utilities, rail and transport, water and wastewater treatment, industrial sites and other critical infrastructure. Corrosion-resistant GRP construction is particularly useful in exposed, coastal and remote locations.
EV Charging and Low-Carbon Infrastructure
Commercial EV charging hubs, fleet depots, renewable energy installations and battery storage projects can require new or upgraded electrical infrastructure. Depending on the approved design, this may include DNO or IDNO intake equipment, HV switchgear, transformers, metering and LV distribution equipment.
SGI designs and manufactures bespoke GRP cabinets and enclosures around the equipment layout, site conditions and relevant network-operator or asset-owner specification. Options include separate access compartments, cable entries, equipment mounting arrangements, ventilation, security features and interfaces with concrete bases, cable trenches and service ducts.
Bespoke DNO Cabinets Designed Around Your Project
Equipment dimensions, cable routes, civil interfaces and network-operator specifications vary between projects. SGI Composites can manufacture a bespoke DNO enclosure around the requirements supplied by the client, electrical designer, contractor or network operator, subject to project-specific approval or acceptance.
Size and configuration
Custom dimensions accommodate the available footprint, equipment layout and required clearances. Options include wall-mounted, floor-standing and larger walk-in configurations, with single-door, double-door or multi-compartment layouts. Modular sections and provision for future expansion can be considered during design.
Access and security
Doors, hinges, stays and locking systems are selected around authorised access requirements. Separate compartments can be provided for the DNO/IDNO, meter operator and customer where required. Openings and clearances must support initial equipment installation, ongoing maintenance and future replacement, as well as routine operation.
Equipment mounting and cable access
Internal backboards, mounting frames, equipment supports, cable-entry provisions and removable panels can be incorporated to suit the approved layout. Mounting loads, cable routes and interfaces with trenches and ducts are considered together, helping maintain access for installation and future equipment changes.
Ventilation and environmental control
Ventilation, louvres and condensation-control provisions are developed around equipment heat losses and site conditions. The design must balance heat dissipation with weather protection, security, fire-performance requirements and the specified IP rating.
Colour, finish and identification
GRP electrical enclosures can be manufactured in project-specific colours and finishes, subject to specification. Safety signage, equipment labels and compartment identification can be incorporated to support operation and maintenance.
DELIVERY AND SITE ASSEMBLY
Enclosures can be supplied fully assembled, in modular sections or for assembly on site, depending on project requirements. Removable panels, sectional construction and designed lifting points can help accommodate restricted access, transport limits and available lifting equipment. Delivery format, assembly responsibilities and foundation interfaces are agreed during the technical review.
Why Choose SGI Composites?
SGI Composites combines specialist composite manufacturing with bespoke design support to develop practical electrical enclosures. We work with project teams to translate approved equipment layouts and specifications into manufacturable housings.
- Bespoke UK manufacture: Enclosures produced around the equipment, site and agreed specification.
- Design and engineering support: Enclosure development, with engineering input and finite element analysis (FEA) where required.
- Modular manufacture: Flexible construction and delivery options for larger housings and restricted sites.
- One-off and repeat production: Support for individual projects and repeat manufacture to agreed designs.
- Coordinated enclosure design: Access, mounting, ventilation, cable routes and civil interfaces considered together.
- Durable GRP construction: Corrosion-resistant housings specified for their intended operating environment.
Send your equipment drawings, applicable specification, required enclosure dimensions and site details to SGI Composites for an initial technical review.