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Machine Shop Power Budget Calculator - Panel Sizing, Phase Balancing & Demand Analysis

Total up your shop equipment loads, check for phase imbalance, and size your electrical service

Free machine shop power budget calculator for planning electrical service and panel capacity in workshops, fabrication shops, and home garages with heavy equipment. A machine shop is one of the most electrically demanding building types per square foot - lathes, mills, welders, plasma tables, air compressors, and dust collectors all draw significant power, many require 240V or three-phase, and several have large inrush currents on startup. This calculator lets you build a complete equipment inventory with nameplate data, then analyzes total connected load, demand load with diversity factors, phase balance, and service entrance sizing. Unlike a simple "add up the amps" approach, it applies NEC demand factors that reflect the reality that not all equipment runs simultaneously. A 100A panel might serve a shop with 150A of total connected load if usage is staggered. The calculator also identifies the single largest motor load (NEC 430.24 requires adding 125% of the largest motor) and checks whether your planned loads fit within the available panel capacity. For three-phase shops, it analyzes load distribution across phases and flags imbalances that cause voltage problems. Results include a recommended service size (100A, 200A, 320A, or 400A), panel schedule outline, and a list of circuits that should be on dedicated breakers.

Pro Tip: The most common mistake in shop electrical planning is sizing the service for today's equipment and forgetting about tomorrow's. A 100A panel seems adequate for a lathe, mill, and drill press. Then you add a MIG welder (50A), a plasma table (40A), and a dust collector (20A). Suddenly you need a 200A upgrade that costs $3,000-5,000 for the panel swap plus utility work. Install 200A from the start - the incremental cost over 100A during initial construction is typically $500-800. That is cheap insurance against a painful upgrade later.

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Machine Shop Power Budget Calculator
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How It Works

  1. Build Your Equipment Inventory

    Add each piece of shop equipment: lathes, mills, grinders, saws, welders, plasma cutters, compressors, dust collectors, and lighting. Enter nameplate voltage, amperage, horsepower, and phase for each item.

  2. Set Usage Patterns

    For each piece of equipment, indicate typical usage: continuous (dust collector, compressor), frequent (lathe, mill), intermittent (welder, plasma, saw), or rare (surface grinder, hoist). The calculator applies appropriate demand factors.

  3. Identify Simultaneous Loads

    Mark which equipment runs at the same time. In a one-person shop, you typically run the dust collector plus one machine tool plus lighting. In a multi-person shop, multiple machines may run simultaneously.

  4. Review Service Sizing

    See total connected load, demand load with NEC factors, the largest motor calculation (125% adder per NEC 430.24), and the recommended service entrance size. Get a panel schedule outline with dedicated circuit assignments.

  5. Check Phase Balance (Three-Phase)

    For three-phase services, review the load distribution across phases A, B, and C. The calculator flags imbalances greater than 10-15% that can cause voltage issues and motor heating. It suggests circuit reassignment to balance the load.

Built For

  • Home machinists planning electrical service for a garage conversion
  • Fabrication shop owners budgeting a panel upgrade for new equipment
  • Electricians sizing service entrance for a new commercial machine shop
  • Woodworkers calculating total demand for a shop with tablesaw, jointer, planer, and dust collector
  • Welding shops evaluating whether existing service can handle an additional welding station

Frequently Asked Questions

Start with nameplate amps for each piece of equipment. Add up all loads for total connected load. Then apply demand factors: the NEC allows you to use 125% of the largest motor plus 100% of all other loads as a starting point. For shop environments where not everything runs at once, further diversity factors (typically 0.6-0.8 for a one-person shop) reduce the demand load. The result determines your minimum service size.
It depends on your equipment. A basic shop with a small lathe (10A), benchtop mill (15A), drill press (8A), grinder (10A), and lighting (15A) can operate on 100A. Add a 220V welder (50A), air compressor (30A), and a few more tools and you're pushing 100A limits. Any shop with a welder over 180A output, a plasma table, or a 5+ HP compressor should plan for 200A service. The cost difference during new construction is modest compared to retrofitting later.
NEC 430.24 requires that the conductor and overcurrent protection for a circuit with multiple motors be sized for 125% of the full-load current of the largest motor plus 100% of all other motors. This accounts for motor starting inrush. For example: a shop with a 15A lathe, 20A mill, and 30A air compressor sizes the feeder for (30 × 1.25) + 20 + 15 = 72.5A, not just 30 + 20 + 15 = 65A.
Single-phase (240V) is standard for residential and most small commercial shops. Three-phase is needed if you have industrial machine tools (many lathes and mills over 3 HP are three-phase), or if your total load exceeds about 150A - three-phase delivers 73% more power through the same wire size. If three-phase is not available from the utility, a rotary phase converter or VFD can run individual three-phase machines from single-phase power, but utility three-phase is more efficient if available.
It depends on your panel capacity. A 220V welder drawing 40-50A and a 30A air compressor together pull 70-80A. On a 100A panel that also serves lighting and other tools, you are at or over capacity. The compressor's motor starting surge (3-6x running amps for a fraction of a second) can trip the main breaker even if the running amps are within limits. Size the panel for the simultaneous load including motor starting surge, or stagger the loads.
Disclaimer: This calculator provides load analysis estimates based on NEC demand calculation methods. Actual electrical service sizing must account for utility requirements, local code amendments, future load growth, and site-specific conditions. All electrical work must be performed by a licensed electrician and inspected per local jurisdiction requirements. Consult with your utility company for service entrance requirements.

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