Planning the electrical system for your workshop is one of the most critical decisions you will make during shop setup. Unlike dust collection or lighting that can be upgraded incrementally, electrical infrastructure requires getting it right from the start. Running wire through finished walls is expensive and disruptive, so proper planning now saves significant time and money later.
A well-designed workshop electrical system provides adequate power for all your current tools while leaving room for future expansion. It ensures motors run at full efficiency, prevents nuisance breaker trips, and keeps you safe from electrical hazards. Whether you are setting up a small garage woodworking shop or a full metalworking facility, understanding your electrical load is the foundation of a functional workspace.
This calculator analyzes your tool selection and estimates total electrical demand using industry-standard demand factors. It accounts for the reality that you will not run all equipment simultaneously and provides recommendations for subpanel sizing, circuit counts, and wire gauges. The results give you a solid starting point for discussions with your electrician and help ensure your workshop electrical system meets both current needs and future growth.
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.
Quality electrical components are essential for safety and reliability. The following products are commonly used in workshop installations and represent good value for their respective categories.
The workhorse of residential subpanels. Indoor/outdoor rated with main breaker, compatible with common Homeline breakers. Provides 20 spaces for circuits, adequate for most serious workshops. NEMA 3R enclosure handles garage environments.
ASIN: B00002N5HN
Compact option for smaller shops or limited wall space. Main lug design requires feed breaker in main panel. Good quality at a lower price point. Works with Siemens QP breakers.
ASIN: B00GTJF3YC
Premium option with room to grow. Copper bus bars, 24 full-size breaker spaces, and main breaker included. Excellent for workshops that may expand over time.
ASIN: B00GZH8LBS
Premium breakers with trip indicator window. Buy in bulk to save money on your workshop buildout. QO series is commercial grade with faster trip times than residential Homeline.
ASIN: B00006B62U
Standard 240V breaker for welders, compressors, and larger equipment. Plug-on design for easy installation. HOM230 model.
ASIN: B00002N5HA
Required for outlets in unfinished areas per NEC. Self-testing with LED status indicator. HOM120GFI model protects the entire circuit.
ASIN: B00002N5HI
Suitable for 60A subpanel feeds up to 50 feet. Contains three 6 AWG conductors plus ground. Romex-type cable for dry interior locations.
ASIN: B000BPEQCC
Cost-effective option for 100A subpanel feeds. Service entrance rated, suitable for conduit or direct burial. Aluminum requires larger gauge but costs less than copper.
ASIN: B002YGPKZY
Perfect for 30A 240V circuits to welders, dryers, or large compressors. Three conductors plus ground, rated for 30 amps.
ASIN: B000BPDJNY
Proper workshop electrical planning requires understanding your current and future needs, local code requirements, and practical installation considerations. This guide covers the key decisions you will face when wiring or upgrading your workshop.
Before planning a workshop subpanel, evaluate your main electrical service. A typical 200A residential service can usually spare 60-100A for a workshop subpanel, depending on household loads. Check your main panel for available space and calculate existing loads. If your main panel is nearly full or you have a 100A service, you may need a service upgrade before adding significant workshop loads.
Look at your main panel slots: each full-size breaker takes one slot, while tandem or half-size breakers share slots. Most panels accept tandem breakers in certain positions only. If you need to add a large feeder breaker for your subpanel but lack space, an electrician can often consolidate existing circuits using tandems to free up positions.
Position your subpanel for convenient access and short wire runs to major equipment. The panel should be at eye level with 36 inches of clear working space in front. Avoid locations that will be blocked by workbenches or stored materials. In garages, consider moisture exposure and choose NEMA 3R rated panels for damp locations.
The feeder cable from your main panel to the subpanel is typically the most expensive part of the installation. Shorter runs require less wire and suffer less voltage drop. Plan the route carefully, considering whether cable will run through finished spaces (requiring protection) or exposed areas (allowing conduit).
Plan more circuits than you think you need. Spaces in your subpanel are inexpensive during initial installation but adding circuits later means more drywall work and electrician visits. For a serious workshop, consider these dedicated circuits:
Install outlets at workbench height (42 inches) rather than standard residential height (12 inches). This keeps cords off the floor and provides convenient access. Place outlets on multiple walls so you are never far from power. Consider the "work triangle" of your main machines and position outlets accordingly.
For 240V equipment, install outlets near planned equipment locations. Moving a 240V outlet later requires significant rewiring. Plan for future equipment by adding an extra 240V circuit or two even if you do not need them immediately. A 30A 240V outlet provides flexibility for various equipment.
Workshop subpanels require proper grounding and bonding per NEC Article 250. The neutral and ground bars must be separate in a subpanel (unlike the main panel where they bond together). A grounding electrode conductor connects to a ground rod or the building grounding system. Your electrician will ensure proper bonding of the equipment grounding conductor throughout the system.
Never rely on conduit alone for grounding in a workshop where vibration and movement are common. Use a dedicated grounding conductor sized appropriately for the feeder amperage. For metal-bodied power tools, proper grounding is critical for shock protection.
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.
Load balancing distributes electrical loads evenly between the two legs (phases) of your electrical service. Your panel alternates circuits between legs, so adjacent breaker positions typically connect to opposite legs. When loads are unbalanced, one leg works harder than the other, reducing overall capacity and efficiency.
For workshop planning, consider which phase each 240V circuit uses (240V circuits use both phases equally) and distribute your 120V circuits so heavy loads are spread between both phases. An electrician can measure phase loading and rearrange circuits if needed. Severe imbalance can cause the neutral conductor to overheat.
In most jurisdictions, yes. Permits are typically required for new subpanels, new circuits, service upgrades, and any work inside electrical panels. Some jurisdictions allow homeowners to pull permits for their own residence while others require licensed electricians for all work.
Unpermitted electrical work creates real risks. Insurance companies may deny claims related to unpermitted work. Home inspectors flag unpermitted modifications, complicating sales. Most importantly, uninspected work may contain safety defects that create fire or shock hazards. The permit and inspection process exists to verify work meets minimum safety standards.
This depends on your skill level, local regulations, and the scope of work. In many areas, homeowners can perform basic electrical work on their own residence with a homeowner permit. However, panel work, service upgrades, and work in commercial buildings typically require licensed electricians.
Even if legally permitted, consider whether you have the knowledge to do the work safely and correctly. Miswired circuits can create fire hazards that may not manifest for years. At minimum, have an electrician perform the panel connections while you handle the simpler tasks of running cable and installing outlets. This hybrid approach reduces cost while ensuring the critical components are professionally installed.
Voltage drop becomes significant on runs over 50 feet. NEC recommends keeping voltage drop under 3% for branch circuits and 5% total for feeder plus branch circuits combined. Excessive voltage drop causes motors to run hot, lights to dim, and equipment to underperform.
The formula considers wire gauge, material (copper vs aluminum), circuit length, and load amperage. Our wire size calculator handles these calculations automatically. As a rule of thumb, increase wire gauge by one size for runs 50-75 feet, and two sizes for runs over 100 feet. For a detached workshop 100 feet from the main panel, you might use 1 AWG aluminum instead of 2 AWG for a 100A subpanel.