UK MCS MIS 3002 Domestic Solar Installation Standard Guide

Key Takeaways

• MIS 3002 Issue 6.0 (effective Date: 18/03/2026) is the definitive UK installation standard for solar photovoltaic systems on permanent buildings up to a maximum DC output of 50kWp.
• Single-phase systems up to and including 16A per phase connect under Engineering Recommendation EREC G98; systems exceeding 16A per phase require EREC G99 prior distribution network approval.
• Where an inverter and battery storage system connected in parallel yield a combined maximum theoretical output greater than 16A, EREC G99 applies.
• Electrical safety rules mandate transient overvoltage protection under BS 7671 regulation 443.4.1, and any arc fault detection function within the inverter must be enabled where present.
• Pre-sale consumer quotes must calculate self-consumption using MGD 003 methodology, presenting separate calculations for solar PV alone and systems paired with home battery storage.

Regulatory Scope and Purpose of MIS 3002 Issue 6.0

In the United Kingdom, achieving formal accreditation under the Microgeneration Certification Scheme (MCS) is the prerequisite for consumer protection, access to the Smart Export Guarantee (SEG), and compliance with home building warranty schemes. Why certification matters across the supply chain is detailed in our MCS certification guide and installer verification methods are covered in our MCS installer directory verification guide.

The technical cornerstone of solar PV quality is Microgeneration Installation Standard MIS 3002. Published by the MCS Charitable Foundation under document control reference MIS 3002 ISSUE 6.0 on Date: 18/03/2026:

• System Capacity Boundary: The standard specifies the requirements for MCS Contractors undertaking the supply, design, installation, set to work, commissioning and handover of solar photovoltaic (PV) systems supplying permanent buildings and normally connected in parallel to the electricity distribution network up to a maximum DC output of 50kWp.
• Target Applications: Domestic dwellings, community buildings, and small commercial premises. Systems exceeding 50kWp transition into commercial ENA G99 Type B engineering.

Grid Interconnection: EREC G98 vs EREC G99 Thresholds

Grid compliance is strictly delineated by single-phase alternating current thresholds:

The 16A EREC G98 Connection Standard

For domestic properties, EREC G98 governs micro-generators operating at or below 16A per phase:

• Under MIS 3002, installations up to and including 16A per phase follow standard G98 notification procedures, allowing installers to connect the system and notify the local Distribution Network Operator (DNO) within 28 days.
• Full procedural guidance is available in our EREC G98 grid connection guide.

The EREC G99 Prior Approval Requirement

Where system capacity surpasses the 16A limit, simplified notification is prohibited:

• In EREC G99 for installations exceeding 16 A per phase, the contractor must submit a formal connection application and receive permission to connect from the DNO prior to commissioning.
• Crucially, clause 5.1.7 establishes that where a solar PV array and an electrical energy storage system (EESS) are connected in parallel to the same single-phase AC supply, if the equipment gives a combined maximum theoretical output greater than 16 A, EREC G99 applies.
• Detailed fast-track and standard G99 application workflows are documented in our EREC G99 connection guide.

Electrical Safety and Surge Protection: BS 7671 Reg 443.4.1

MIS 3002 enforces rigorous electrical protection standards aligned with BS 7671 (IET Wiring Regulations) and the 2nd Edition of the IET Code of Practice for Grid Connected Solar Photovoltaic Systems:

Transient Overvoltage and SPDs

Lightning and grid switching transients can destroy inverter electronics and induce severe roof fire risks. Under clause 5.3.3:

• BS7671:2018+A2:2022 (regulation 443.4.1) stipulates the circumstances when protection against transient overvoltage must be provided.
• Surge Protection Devices (SPDs) must be provided unless the owner of the installation is prepared to tolerate the risk following a documented risk assessment.
• While some inverters incorporate integrated DC surge protection, external Type 1 or Type 2 SPDs must be installed at the origin of the installation where required.

Array Frame Earthing

Array earthing on domestic roofs requires deliberate design engineering. MIS 3002 specifies that where the decision is taken by the system designer to not provide either protective or functional earthing, justification must be documented in the design file. When functional earthing is fitted, continuity must be verified during commissioning.

Arc Fault Detection and Cable Sizing

1. AFCI Protection: Clause 5.6.7 mandates that where present, any arc fault detection function within the inverter shall be enabled.
2. AC Voltage Drop & Anti-Tripping: Cable sizing between the origin of the installation (suppliers cut out) and the AC input terminals of the inverter must restrict voltage drop to prevent inverters nuisance-tripping due to over-voltage on sunny days.

Performance Estimation and Consumer Transparency: MGD 003

To prevent misleading sales practices, MIS 3002 standardizes pre-sale energy generation and financial payback projections:

• Self-Consumption Methodology: An estimate of self-consumption shall be calculated in accordance with MGD 003: ‘Determining the Electrical Self-Consumption of Domestic Solar Photovoltaic (PV) Systems’.
• Dual-Quote Disclosure: The quotation must separately present:
• • Expected solar PV self-consumption (PV Only) kWh.
  • Expected solar PV self-consumption (with EESS) kWh when battery storage is proposed.
• Transparent Assumptions: Estimates based on remote desktop evaluations must carry mandatory caveats informing the client that actual performance depends on on-site shading and array orientation.

Testing, Commissioning, and Handover Documentation

Under Section 6 of MIS 3002, the installation is incomplete until thorough electrical verification and client handover occur:

1. Testing Protocols: The contractor must perform mandatory DC tests prior to energisation:

• • Open-circuit voltage (Voc) measurement.
  • Short-circuit current (Isc) measurement.
  • Insulation resistance testing between live conductors and earth: Pos – Earth (MΩ) and Neg – Earth (MΩ).
  • Earth continuity verification where array bonding is installed.

2. Immediate Handover Rule: The contractor is required to handover the installation immediately following commissioning.
3. Handover Pack Contents: In accordance with the Model Handover Document (Appendix E), the customer pack must contain the MCS certificate, Electrical Installation Certificate (EIC), inverter manual, warranty documentation, and emergency shutdown procedures.

When to Contact Your MCS Contractor

Homeowners should refer to their MCS handover documentation and contact their certified contractor if:

• The inverter displays grid overvoltage alarms or repeatedly trips during peak midday solar generation.
• You plan to add an AC-coupled battery or EV charger that may push total export capacity beyond 16A per phase.
• DC isolation resistance drops below 1.0 MΩ during routine periodic inspection and testing.