What cable size do I need for a 5kW solar inverter?

A 5kW single-phase inverter outputs approximately 22A at 230V. For the AC side, 4mm² cable is suitable for runs up to about 20m, or 6mm² for longer runs. Always check voltage drop for your specific cable length.

Do solar PV systems need RCD protection?

Yes, the AC circuit from inverter to consumer unit requires 30mA RCD protection under BS 7671. Most modern inverters have integrated RCD protection, but external RCD at the consumer unit is still required. Type A or Type B RCD depending on inverter type.

What's the difference between DC and AC cable sizing for solar?

DC cables connect panels to inverter - they carry high voltage DC (300-600V typically) and must be solar-rated with UV resistance. AC cables connect inverter to consumer unit - standard cables sized for inverter output current. Different calculations and cable types for each.

What MCB rating for a solar inverter?

MCB rating depends on inverter output current. 3.6kW = 16A MCB, 5kW = 25A or 32A MCB, 8kW = 40A MCB. Type B MCBs are standard. The circuit must be dedicated - not shared with other loads.

Do I need DNO permission for solar panels?

Yes, DNO notification is required. Systems up to 3.68kW per phase can use G98 notification (simple form). Larger systems need G99 application and approval before installation. Your MCS installer handles this paperwork.

How do I size DC cables for solar strings?

DC cable sizing depends on string short-circuit current (Isc), cable length, and temperature derating (roof installations get very hot). Typically 4mm² or 6mm² solar cable for residential strings. Use solar-specific cable rated for the system voltage.

What about battery storage cable sizing?

Battery systems have their own requirements - typically 16A-32A circuits depending on charge/discharge rate. High-power batteries (5kW+) may need 6mm² or 10mm² cables. Follow manufacturer specifications and ensure adequate MCB protection.

Can I connect solar to an existing consumer unit?

If the consumer unit has a spare way and adequate capacity, yes. However, older units may need upgrading for RCD protection or capacity. A dedicated isolator switch near the inverter is also required for safe maintenance.

G98 and G99 are DNO connection standards. G98 is for small systems up to 3.68kW per phase - simple notification, connect and notify within 28 days. G99 is for larger systems - requires application, approval, and possibly network studies before installation.

Do solar cables need to be fire-rated?

DC cables on roofs should be solar-rated (UV resistant, double insulated). In buildings, cables may need fire-resistant properties depending on the route. LSZH (Low Smoke Zero Halogen) cables are recommended for internal runs to reduce fire risk.

Back to Cable Sizing Calculator

Solar PV & Battery Cable Sizing Calculator

Calculate the correct cable size for solar PV arrays, inverters, and battery storage systems

Solar PV Cable Quick Facts

AC cable from inverter typically needs 6mm² or 10mm² for 3.6-8kW systems
DC cable sizing depends on string voltage and current
Battery systems may need separate supply circuit (16A-32A)
MCS certification required for SEG payments
G98/G99 DNO notification required for grid connection

Cable Size Calculator

BS 7671:2018+A2:2022 compliant

1. Load Current

2. Cable Length (meters)

3. Installation Method

Lighting circuit (3% voltage drop limit)

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Common Solar PV & Battery Installations

3.6kW single-phase inverter (16A)

16A MCB, 2.5mm² or 4mm² cable depending on length

5kW single-phase inverter (22A)

32A MCB, 4mm² or 6mm² cable for AC side

8kW single-phase inverter (35A)

40A MCB, 6mm² or 10mm² cable for AC side

Battery storage system (5-10kWh)

Check manufacturer specs - typically 16A-32A dedicated circuit

Three-phase 10kW+ system

3-phase supply required, 16A per phase, 4mm² 5-core cable

Complete Your Renewable Energy Installation

Installing solar PV often goes hand-in-hand with other electrical upgrades. Many customers add EV charging to maximise self-consumption of solar energy. For complete renewable heating, our air source heat pump cable calculator covers the heating side. For outbuilding installations with solar, check our garden office cable sizing guide.

Solar PV Cable Sizing

Solar PV cable sizing covers both DC cables (from panels to inverter) and AC cables (from inverter to consumer unit). DC cables must handle high voltages (up to 600V) and are sized for string current with derating for roof temperatures. AC cables are sized like any circuit but must handle continuous inverter output current.

Solar PV Installation Costs - Electrical Only (2024)

Typical UK electrical installation costs. Does not include panels, inverter, or battery hardware.

Installation Scenario	Materials	Labour	Total
AC cable run, consumer unit to inverter (<10m)	£60-120	£100-180	£160-300
AC cable run, longer distance (10-25m)	£120-220	£150-280	£270-500
DC cable from roof to inverter	£150-350	£200-400	£350-750
Battery system wiring	£100-250	£150-300	£250-550
Consumer unit upgrade for solar	£150-300	£200-350	£350-650

Prices as of 2024. Full system installation costs vary significantly.

MCS Certification Requirements

MCS (Microgeneration Certification Scheme) certification is required to receive Smart Export Guarantee (SEG) payments for exported electricity. MCS requires specific cable sizing, installation methods, and documentation. Only MCS-certified installers can register systems for SEG eligibility.

Smart Export Guarantee (SEG)

SEG is the UK scheme where energy suppliers pay for electricity exported to the grid from solar PV systems. To receive SEG payments, your system must be installed by an MCS-certified installer with proper certification. Rates vary by supplier - typically 3-15p per kWh exported.

DC Isolator Requirements

Solar PV systems require DC isolators at both the array (roof level) and inverter. These allow safe disconnection of the DC circuit for maintenance or emergencies. Isolators must be rated for the system voltage (typically 600V DC minimum) and installed to prevent accidental operation.

Frequently Asked Questions

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