Calculate your workshop electrical requirements based on your tool selection. Get recommendations for subpanel sizing, circuit counts, and wire gauges using industry-standard demand factors.
100A main breaker, indoor/outdoor, NEMA 3R rated. Best value for serious workshop subpanels.
View on AmazonTrue RMS, auto-ranging, 1000V CAT III rated. Essential for verifying circuits and troubleshooting.
View on Amazon6 AWG copper for 60A subpanel feeds. Three conductors plus ground, NM-B rated for dry locations.
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Select your equipment to calculate total demand load, required circuits, and subpanel recommendations.
Based on your equipment selection, you need a dedicated subpanel for your workshop.
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Electrical load calculations determine how much power your workshop needs by analyzing each piece of equipment and applying engineering principles established in the National Electrical Code (NEC). The process involves three key concepts: connected load, demand factor, and continuous versus non-continuous loads.
Your connected load is the total amperage if every piece of equipment ran at full power simultaneously. However, you never actually operate this way. You cannot run a table saw and planer at the same time while welding. The demand load applies a realistic factor (typically 40-60% for workshops) to account for actual usage patterns. This is why a shop with 150A of connected load might only need a 100A subpanel.
When calculating total load, 240V equipment counts differently than 120V. A 240V circuit uses both "legs" of your electrical service, so a 30A 240V welder uses 30 amps from each leg. For demand calculations, 240V loads are often converted to equivalent 120V amperage (doubled) to properly size the main service capacity. Our calculator handles this automatically.
Different equipment categories have different demand factors. Lighting and HVAC are often at 100% because they run continuously during shop use. Stationary power tools might be 40-50% because only one typically runs at a time. Welding equipment uses a duty cycle factor based on realistic welding patterns. These factors, established through decades of electrical engineering practice, ensure your system is adequately sized without excessive oversizing.
Electrical work can be dangerous and is regulated by local building codes. The information provided here is for planning purposes only and does not replace professional electrical design or licensed electrician installation.
For most home workshops, a 60-100A subpanel fed from your existing main service is sufficient. A 100A subpanel can handle a full woodworking shop with cabinet saw, planer, jointer, dust collector, and lighting plus a welder up to 200A output capacity. Only dedicated commercial shops or facilities with multiple large welders running simultaneously need 200A workshop service.
The real question is whether your main panel can spare the capacity. A 200A main service can typically allocate 60-100A for a shop subpanel while maintaining adequate power for household loads. If you have 100A main service and want a serious workshop, you may need a service upgrade first.
Always size your subpanel for future growth, not just current needs. Adding circuits later is expensive compared to installing a larger panel initially. For hobbyist woodworking with 120V tools only, a 60A panel with 12 spaces works fine. For serious shops with 240V equipment, choose a 100A panel with 20-24 spaces minimum.
Consider both amperage and circuit spaces. A 100A panel with only 8 spaces will limit your flexibility even though it has adequate power capacity. Look for panels with at least 20 full-size breaker spaces. Tandem breakers can double circuit count in some positions, but dedicated circuits for major equipment should use full-size breakers.
Use 240V for motors 2HP and larger whenever the equipment offers a 240V option. At 240V, a motor draws half the current of the equivalent 120V motor for the same power output. This means smaller wire, longer allowable runs without voltage drop issues, and reduced heat in both wire and motor. Most cabinet table saws, planers over 13 inches, larger jointers, and dust collectors over 2HP offer 240V operation.
For welding equipment, 240V is essentially mandatory for anything beyond a small 120V flux-core welder. MIG welders capable of welding 1/4 inch steel and all TIG welders require 240V. The higher voltage allows the welder to draw adequate power without overwhelming standard 15-20A household circuits.
Wire size depends on amperage and distance from main panel to subpanel. For copper NM-B cable: 60A requires 6 AWG, 100A requires 3 AWG. For aluminum SER cable (more common for long runs due to cost): 60A requires 4 AWG, 100A requires 1 AWG or 2-2-2-4 SER cable.
Add one wire size for runs exceeding 50 feet to compensate for voltage drop. A 75-foot run to a detached garage might need 2 AWG copper instead of 3 AWG for a 100A subpanel. Always use 4-wire cable (two hots, neutral, ground) for subpanels per current NEC requirements. The ground and neutral must remain separate in the subpanel.
NEC requires GFCI protection for all 125V 15A and 20A receptacles in garages and accessory buildings including workshops. This applies to both attached garages and detached shop buildings. The requirement exists because workshop floors are often damp concrete, creating shock hazards if insulation fails on equipment.
You can provide GFCI protection at the breaker (protecting the entire circuit) or at the first outlet in a daisy-chain. GFCI breakers are more expensive but eliminate the need to locate and reset a tripped GFCI outlet. Some woodworkers report nuisance trips with dust collectors on GFCI circuits due to motor startup inrush, though modern GFCI breakers are more tolerant of this. Equipment on 240V circuits typically does not require GFCI protection for standard workshop use.
Any tool drawing more than 50% of a circuit's capacity should have a dedicated circuit. This includes table saws, planers, jointers, large dust collectors, air compressors, welders, and HVAC equipment. The high inrush current when motors start can trip breakers if other loads share the circuit.
Even if a tool's running amperage seems low enough to share, motor startup can draw 3-5 times running current for a fraction of a second. A 12A planer might draw 40+ amps momentarily at startup. Dedicated circuits prevent nuisance trips and ensure full voltage reaches the motor for optimal performance and longevity.