20A or 30A? Driven by equipment nameplate.
Commercial dedicated circuit sizing follows equipment nameplate × 1.25 for continuous duty. Most common sizes are 20A and 30A; selection depends on equipment.
By Steven Lockhart · Reviewed by Alex Towery, C-10 #989290
Updated 2026-06-16
Commercial dedicated circuit sizing: equipment nameplate amperage × 1.25 for continuous-duty equipment (running 3+ hours). 20A circuits handle equipment up to 16A nameplate (16A × 1.25 = 20A). 30A circuits handle 24A nameplate. Larger equipment (40A, 50A, 60A circuits) for high-amperage commercial equipment. Wrong sizing creates safety risk (undersized) or wastes cost (oversized). Match circuit size to equipment requirement.
01How circuit sizing actually works.
NEC requires continuous-duty derating for equipment running 3+ hours at full load — circuit must be sized 125% of equipment full-load current. For 16A equipment running continuously: 16A × 1.25 = 20A required circuit. Most office equipment (computers, printers, small appliances) draws under 16A and fits 20A circuits. Commercial-scale equipment (commercial dishwashers, large refrigeration, EV chargers, induction cooking) often exceeds 16A and requires 30A or larger circuits.
Practical sizing: identify equipment full-load amperage from nameplate, multiply by 1.25 for continuous-duty, round up to standard circuit size. 14A nameplate → 17.5A required → 20A circuit. 24A nameplate → 30A required → 30A circuit. 36A nameplate → 45A required → 50A circuit. Standard breaker sizes: 15, 20, 30, 40, 50, 60A typical for commercial branch circuits.
02Common equipment by circuit size.
20A circuits — most common
Office workstations, light commercial kitchen equipment, retail equipment, network closet equipment. Standard for most commercial dedicated needs. Conductor 12 AWG copper for typical runs.
30A circuits — larger commercial equipment
Commercial dishwashers, water heaters, larger refrigeration compressors, smaller cooking equipment. 10 AWG conductor for typical runs. Receptacle types specific to 30A (NEMA 6-30, L6-30 common).
40A+ circuits — high-amperage equipment
Commercial ranges, larger walk-in compressors, EV chargers, induction cooking, large HVAC. Conductor 8 AWG or larger. Hardwired typically (no plug); sometimes NEMA 14-50 receptacle for portable equipment up to 50A.
03Avoid common sizing errors.
Don't undersize for cost savings. Saving $80-$200 in conductor cost by going one circuit size smaller can cause equipment performance issues (voltage drop, breaker tripping under load) or safety issues (overheating, fire risk). Code minimum is the floor; sizing to actual equipment need is the right approach.
Don't oversize 'just in case.' Putting a 60A circuit on equipment needing 20A wastes conductor cost ($200-$500 per circuit), may not provide adequate fault protection (oversized breaker doesn't trip on smaller fault currents), and complicates equipment connection. Size to actual need with modest margin only when future equipment additions are realistic.
Common questions.
How do I know my equipment amperage?
Equipment nameplate states full-load amperage (FLA) along with voltage. Spec sheets from manufacturer provide same information. We translate equipment specs into circuit sizing during quote phase.
What if equipment changes after install?
Within similar amperage: circuit reusable. Significantly different amperage: rework required. 30A circuit can handle 20A equipment (oversized but compliant); 20A circuit can't safely handle 30A equipment. Plan for likely equipment scope at install; adjust later for major changes.
Is dedicated circuit always required?
NEC requires dedicated for specific equipment categories: kitchen equipment, refrigeration, sometimes HVAC, equipment listed for dedicated. Best practice extends to any meaningful commercial equipment for reliability. Shared circuits work for small equipment combined; dedicated for important or larger equipment.
How do you handle pricing — flat fee or hourly?
Both, depending on scope. Routine service calls and predictable scope (panel replacement, EV charger install, transfer switch install, fixture replacement) are flat-fee quoted up front. Diagnostic visits and emergency scope are hourly because we don't know what we'll find. Either way, you get a written quote before work starts on anything significant, and we don't proceed beyond the quote without your sign-off.
How quickly can you schedule?
Depends on scope and season. Emergency dispatch: same-day across Marin County (1-3 hours business hours, 1-4 hours after-hours). Same-day standard service: 3-6 hours from call when capacity allows; otherwise next business day. Scheduled service work: 1-3 weeks typical. Larger projects requiring permits and PG&E coordination: 4-12 weeks depending on scope. We're upfront about timeline at the quote stage.
What warranty do you offer on work?
Our standard residential warranty: 2 years on labor, manufacturer warranty on parts (varies by product — typically 1-10 years). Major installs (panels, generators, EV chargers) often have longer manufacturer warranties (5-10 years). If there's an issue with our work in the warranty period, we come back and fix it at no cost. We also stand behind work past warranty — repeat customers and referrals matter more than a transactional fix.
Are you licensed and insured?
Yes. California State License Board C-10 Electrical Contractor #989290, in good standing. Carry general liability insurance and workers' compensation insurance as required by California law. Bondable on projects requiring it. Happy to provide proof of insurance to clients or property managers on request. License lookup: cslb.ca.gov.
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