What cable size do I need for a detached garage?

For a typical detached garage with sockets and lighting, 6mm² SWA on a 32A circuit handles most needs. Long runs (20m+) may need 10mm² to keep voltage drop acceptable. Consider future additions like EV charging when sizing.

Can I run a welder from a standard socket?

Small 13A welders can use standard sockets, but most MIG/TIG welders need 16A-32A supplies. Check your welder's specifications. Larger welders need dedicated circuits to prevent voltage drop affecting weld quality and tripping shared circuits.

What MCB type for workshop equipment?

Type C MCBs are recommended for workshops with motors (compressors, lathes, saws). They handle inrush currents up to 10x rated current without tripping. Type B MCBs (5x) may nuisance trip on motor starts.

Do I need a consumer unit in my garage?

For simple supplies (one circuit), a fused connection from the house is acceptable. For workshops with multiple circuits or heavy equipment, a garage consumer unit provides better protection, easier fault finding, and room for expansion.

What about three-phase for workshops?

Three-phase is beneficial for large motors (5HP+), commercial welders, or multiple high-power machines. It requires DNO application and 5-core SWA cable. Many domestic properties don't have three-phase available without significant upgrade cost.

How do I size cable for multiple machines?

Calculate total connected load but apply diversity - not all machines run simultaneously. Typical diversity: 100% largest load + 50% of remainder. A workshop with 3kW welder + 2kW compressor + 1kW tools = 3kW + 1.5kW = 4.5kW design load.

Is RCD protection required for garages?

Yes, 30mA RCD protection is required for all garage and workshop circuits under BS 7671. This can be at the house consumer unit or in a local garage unit. Consider time-delayed RCDs if using RCDs at both ends.

Can I add EV charging to my garage supply?

EV chargers typically need dedicated 32A circuits. If your garage already has a 32A supply, adding EV charging may overload it. Consider upgrading to a larger submain that can feed both workshop circuits and EV charger.

What burial depth for garage SWA cable?

Minimum 450mm under garden/grass, 600mm under driveways. Use sand bedding and warning tape. Avoid running near other services. Mark the cable route for future reference.

Do I need Part P notification for garage electrics?

Yes, new circuits to garages and outbuildings are notifiable under Part P. This includes new supplies, consumer unit installations, and significant alterations. Work must be done by a registered competent person or inspected by Building Control.

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Garage & Workshop Cable Sizing Calculator

Calculate the correct cable size for garage and workshop electrical supplies

Garage & Workshop Cable Quick Facts

Typical garage supply: 32A radial or 40A for heavy equipment
Welders and compressors have high inrush current - consider Type C MCB
SWA cable required for buried runs to detached garages
Consider future needs - size for expansion
RCD protection mandatory for garage/workshop circuits

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 Garage & Workshop Installations

Basic garage - lighting + sockets only

20A or 32A circuit, 4mm² cable for typical runs

Home workshop - power tools

32A circuit, 6mm² SWA for detached, consider dedicated circuits

MIG/TIG welder (13A-32A)

Dedicated 32A circuit minimum, check welder specifications

Large compressor (3-5HP)

Dedicated 32A circuit, Type C MCB for motor inrush

Professional workshop - multiple machines

Submain to garage consumer unit, 63A-100A supply

Related Outbuilding & Vehicle Charging

Many garage installations include EV charger circuits - plan capacity for both workshop and charging needs. For garden offices and studios, see our dedicated garden office cable calculator. Some workshops add air source heat pumps for heating.

Garage & Workshop Cable Sizing

Garage and workshop cable sizing determines the conductor cross-sectional area (mm²) needed to safely supply power tools, welders, compressors and other equipment. Key factors include total connected load, motor inrush currents, cable run length (especially for detached buildings), and future expansion needs.

Garage & Workshop Installation Costs (2024)

Typical UK installation costs including cable, groundwork for detached buildings, and labour.

Installation Scenario	Materials	Labour	Total
Attached garage supply (<10m)	£80-150	£150-280	£230-430
Detached garage, short run (<15m)	£200-350	£250-400	£450-750
Detached garage, medium run (15-30m)	£350-550	£350-500	£700-1050
Workshop with mini consumer unit	£250-400	£300-450	£550-850
Three-phase workshop supply	£600-1200	£500-900	£1100-2100

Prices as of 2024. Three-phase costs vary significantly by DNO and location.

Motor Inrush Current

Motors in power tools, compressors and welders draw 5-8 times their running current when starting. This inrush can trip Type B MCBs. Type C or Type D MCBs have higher trip thresholds to handle motor starting currents while still providing protection. Check equipment specifications for MCB requirements.

Garage Consumer Unit

A garage consumer unit (often called a garage unit) provides local protection and isolation for workshop circuits. Typically includes main switch, RCD protection, and MCBs for individual circuits (sockets, lighting, dedicated equipment). Allows expansion without returning to the house for every addition.

Submain vs Final Circuit

A final circuit supplies equipment directly (e.g., 32A socket circuit). A submain supplies a distribution board (consumer unit). For workshops needing multiple circuits, a submain to a garage consumer unit is more practical than running multiple final circuits from the house.

Frequently Asked Questions

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Check long runs to detached garages

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