Workshop Electrical Guide 2026: Subpanel Sizing & Circuit Planning

Workshop Electrical Basics

Before diving into planning, let's establish the fundamentals. Understanding these concepts helps you make informed decisions and communicate effectively with electricians.

Voltage: 120V vs. 240V

In North America, residential electrical service provides both 120V and 240V power. Standard outlets are 120V, while heavy-duty circuits for large appliances and shop equipment use 240V.

Why 240V for shop equipment? For the same power output, 240V requires half the amperage of 120V. This means smaller wire gauges, less heat generation, and more efficient motor operation. A 3 HP table saw at 240V draws about 12 amps, while the same motor at 120V would draw 24 amps—requiring much heavier wiring.

Amperage and Load

Amperage (amps) measures the flow of electrical current. Every circuit has an amperage rating—typically 15A or 20A for 120V circuits, and 20A, 30A, or 50A for 240V circuits. Exceeding a circuit's rating trips the breaker.

Connected load is the total amperage of everything that could be plugged in simultaneously. Demand load accounts for the fact that you don't run everything at once—it's typically 60-80% of connected load for shop calculations.

Single Phase vs. Three Phase

Residential and most small shops use single-phase power. Three-phase power is more efficient for large motors but requires special (and expensive) service installation. Unless you're running industrial equipment over 5 HP, single-phase is adequate.

Calculate Your Electrical Load

Use our calculator to determine your total load, demand load, and subpanel requirements.

Calculating Your Electrical Load

Accurate load calculation ensures your electrical system has adequate capacity without excessive over-building. Here's how to approach it:

Step 1: List All Equipment

Create a comprehensive list of everything that will draw power in your shop. Include:

• Stationary power tools: Table saw, planer, jointer, bandsaw, drill press
• Dust collection: Dust collector, air filtration unit
• Climate control: Heater, mini-split, fans
• Lighting: Overhead lights, task lights
• Air compressor: If pneumatic tools are used
• Miscellaneous: Battery chargers, radio, refrigerator

Step 2: Determine Amperage for Each Item

Find the amperage rating on each tool's nameplate. Common workshop equipment amperages:

• Table Saw (3 HP, 240V): 12-15 amps
• Table Saw (1.75 HP, 120V): 13-15 amps
• Planer (15", 240V): 15-20 amps
• Jointer (8", 240V): 12-15 amps
• Dust Collector (1.5 HP): 12 amps at 120V, 6 amps at 240V
• Air Compressor (5 HP): 20-24 amps at 240V
• Bandsaw (14"): 6-8 amps at 120V
• Router (3 HP): 15 amps at 120V
• Shop Vacuum: 8-12 amps at 120V

Step 3: Calculate Connected Load

Sum all equipment amperage, separating 120V and 240V loads. Convert to watts for an apples-to-apples comparison:

Watts = Volts × Amps

Example: A 3 HP table saw at 240V drawing 15 amps = 3,600 watts

Step 4: Apply Demand Factor

Since you won't run everything simultaneously, apply a demand factor. For workshop calculations:

• First 10,000 watts: 100% (full load)
• Remaining watts: 40-50%

This recognizes that while your table saw runs, your planer is off, and vice versa.

Subpanel Sizing

A dedicated subpanel for your workshop is almost always worthwhile. It provides adequate circuits without overloading your home's main panel, makes troubleshooting easier, and allows future expansion.

Common Subpanel Sizes

• 60-amp subpanel: Suitable for basic hobby shops with mostly 120V tools and perhaps one 240V tool. Limited expansion capacity.
• 100-amp subpanel: The sweet spot for most home workshops. Handles multiple 240V tools, dedicated dust collection, and ample 120V circuits.
• 125-amp or 150-amp subpanel: For larger shops with multiple stationary machines, welders, or extensive 240V requirements.
• 200-amp subpanel: Professional-level shops or those planning significant expansion.

Sizing Recommendations by Shop Type

Based on typical equipment and usage patterns:

• Small hobby shop (under 200 sq ft): 60-amp minimum, 100-amp recommended
• Medium shop (200-500 sq ft): 100-amp standard
• Large shop (500+ sq ft): 125-amp or 200-amp
• Automotive shop with welder: 150-200 amp
• Metalworking shop: 150-200 amp (welding and plasma require significant capacity)

Circuit Planning

Well-planned circuits prevent nuisance trips and ensure reliable power where you need it. Here's how to approach circuit allocation:

Dedicated Circuits

These tools should have their own dedicated circuits:

• Table saw: 240V, 20-30 amp depending on motor size
• Planer: 240V, 20 amp typically
• Jointer: 240V, 20 amp typically
• Dust collector: 240V preferred, 20 amp
• Air compressor: 240V, 20-30 amp depending on HP
• Welder: 240V, 30-50 amp depending on type

General Purpose Circuits

120V general-purpose circuits serve outlets for portable tools, lighting, and miscellaneous equipment. Plan for:

• 20-amp circuits for all shop outlets (15-amp circuits are undersized for shop use)
• One circuit per 2-3 duplex outlets maximum
• Separate circuit for each major work zone (bench area, assembly area, machine area)
• Dedicated lighting circuit so tool startup doesn't affect lights

Sample Circuit Layout for a Medium Shop

• Circuit 1-2: Table saw (240V, 20A)
• Circuit 3-4: Planer (240V, 20A)
• Circuit 5-6: Dust collector (240V, 20A)
• Circuit 7: Bench outlets - south wall (120V, 20A)
• Circuit 8: Bench outlets - north wall (120V, 20A)
• Circuit 9: Machine area outlets (120V, 20A)
• Circuit 10: Assembly area outlets (120V, 20A)
• Circuit 11: Overhead lighting (120V, 15A or 20A)
• Circuit 12: Spare/expansion (120V, 20A)

240V Circuits for Power Tools

Most stationary woodworking machines with motors over 1.5 HP benefit from 240V power. The advantages include:

• Lower amperage draw: Smaller wire required
• More efficient motor operation: Less heat, longer motor life
• Better starting torque: Motors start more reliably under load
• Reduced voltage drop: Especially important on longer runs

Common 240V Configurations

• NEMA 6-20: 240V, 20 amp - Most common for shop tools
• NEMA 6-30: 240V, 30 amp - Larger tools, some welders
• NEMA 6-50: 240V, 50 amp - Large welders, plasma cutters
• NEMA 14-30: 240V, 30 amp with neutral - Some equipment needs this

Converting Tools to 240V

Many dual-voltage motors can be converted between 120V and 240V by reconfiguring internal wiring. Check your tool's manual for instructions. This is typically a matter of repositioning jumper wires on the motor terminal block.

Wire Sizing and Voltage Drop

Proper wire sizing ensures safe operation and minimizes voltage drop. Undersized wire causes heat buildup (fire risk) and voltage drop (motor damage).

Wire Gauge by Circuit Amperage

• 15-amp circuit: 14 AWG minimum
• 20-amp circuit: 12 AWG minimum
• 30-amp circuit: 10 AWG minimum
• 40-amp circuit: 8 AWG minimum
• 50-amp circuit: 6 AWG minimum

Voltage Drop Considerations

For long wire runs, you may need to upsize wire to prevent voltage drop. Excessive voltage drop (over 3% on branch circuits) causes:

• Motors running hot and potentially burning out
• Reduced motor power and efficiency
• Dimming lights when motors start
• Equipment malfunction

For runs over 50 feet, consider upsizing wire by one gauge. For runs over 100 feet, upsize by two gauges.

Subpanel Feeder Sizing

The wire running from your main panel to the subpanel must be sized for the subpanel's amperage:

• 60-amp subpanel: 6 AWG copper or 4 AWG aluminum
• 100-amp subpanel: 3 AWG copper or 1 AWG aluminum
• 125-amp subpanel: 2 AWG copper or 1/0 AWG aluminum
• 200-amp subpanel: 2/0 AWG copper or 4/0 AWG aluminum

Outlet Placement Strategy

Thoughtful outlet placement reduces extension cord clutter and improves safety. Plan outlets based on how you'll actually work in the space.

Wall Outlets

• Workbench area: Outlets every 4-6 feet at bench height (42")
• Perimeter walls: Outlets every 6-8 feet at standard height
• Above outlets: Mount at 48" for easy access above stored materials
• 240V outlets: Position near intended equipment locations

Island and Floor Outlets

For tools positioned away from walls (table saw, assembly table), consider:

• Ceiling drops: Retractable cord reels mounted on ceiling
• Floor boxes: Flush-mount outlets in concrete floors
• Power columns: Utility poles from floor to ceiling with outlets

Dedicated Dust Collector Outlet

Position your dust collector outlet to minimize cord runs. Many shops place the collector against an exterior wall with its own 240V outlet. See our Dust Collection Guide for placement considerations.

Shop Lighting Circuits

Good lighting is essential for safety and quality work. Dedicate one or more circuits to lighting so tool startup doesn't cause dimming.

Lighting Load Calculation

Modern LED shop lights draw relatively little power. A typical 4-foot LED shop light draws 40-50 watts. You can put many lights on a single 15-amp circuit (1,800 watts capacity), but dividing across two circuits adds redundancy.

Switched Circuits

Consider how you want to control your lights:

• Single switch: Simple, all lights on or off
• Zone switching: Separate switches for different areas
• Occupancy sensors: Lights activate automatically when you enter
• Dimmer capability: LED-compatible dimmers for adjustable output

Electrical Safety

Workshop electrical systems require attention to safety beyond typical residential installations:

GFCI Protection

Ground Fault Circuit Interrupters (GFCIs) are required in garages and workshops. They protect against electrocution by detecting current imbalances. Install GFCI protection via:

• GFCI breakers: Protect the entire circuit from the panel
• GFCI outlets: Protect that outlet and downstream outlets

Note: GFCIs can trip on some motors, particularly older equipment with slight insulation breakdown. This is actually the protection working—have suspect equipment checked by a professional.

Proper Grounding

All outlets, boxes, and equipment must be properly grounded. In a shop environment with metal machinery and potentially damp conditions, proper grounding is critical for safety.

Clear Labeling

Label every circuit clearly at the subpanel. In an emergency, you need to know exactly which breaker controls what equipment.

Permits and Inspections

Most jurisdictions require permits for electrical work beyond simple outlet replacement. Subpanel installation always requires a permit.

Why Get a Permit?

• Safety: Inspector catches errors before they cause problems
• Insurance: Unpermitted work may void insurance coverage
• Resale: Disclosure requirements for unpermitted work
• Legal: Required by law in most areas

DIY vs. Licensed Electrician

Many jurisdictions allow homeowners to do their own electrical work with proper permits. However, electrical work requires knowledge and carries real risks. Consider hiring a licensed electrician if:

• You're not confident in your electrical knowledge
• The work involves the main panel or service entrance
• Local codes require licensed contractor work
• You want warranty protection on the work

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