Calculating Electrical Load for New Circuits: Continuous vs Non-Continuous Loads and NEC Rules

Before you size a wire or pick a breaker, you need to answer the fundamental question: how much load is on this circuit? Every other calculation — conductor ampacity, OCPD rating, voltage drop — depends on getting the load number right. Overestimate, and you overbuild. Underestimate, and you get nuisance tripping, overheated conductors, or a red tag from the inspector.

The NEC provides specific methods for calculating branch circuit loads, feeder loads, and service loads. This guide covers the branch circuit and feeder level — the calculations you perform when adding a new circuit to an existing panel or sizing a sub-panel for a new space.

Continuous vs. Non-Continuous Loads: The 125% Rule

This distinction drives every load-to-breaker sizing decision in the NEC, and getting it wrong is one of the most common calculation errors.

Continuous load (NEC Article 100): A load where the maximum current is expected to continue for 3 hours or more. Examples: commercial lighting, electric baseboard heat, sign circuits, EV chargers, data center equipment.

Non-continuous load: A load that cycles on and off or runs for less than 3 hours at maximum current. Examples: residential receptacles, kitchen appliances, bathroom exhaust fans, garage door openers.

Why the 125% Rule Exists

Standard circuit breakers (80%-rated) are designed and tested to carry only 80% of their rating continuously. A 20A breaker will eventually trip if it carries 20A nonstop for 3+ hours — it is designed to carry 16A continuously (20A × 0.80 = 16A). This is not a defect; it is a thermal protection feature that accounts for cumulative heat buildup in the breaker, panel, and conductors.

The NEC addresses this with two parallel requirements per 210.19(A)(1) and 210.20(A):

Conductor sizing: Ampacity must be at least 125% of the continuous load plus 100% of the non-continuous load
OCPD sizing: Rating must be at least 125% of the continuous load plus 100% of the non-continuous load

The formula:

Minimum ampacity = (Continuous load × 1.25) + Non-continuous load

100%-Rated Breakers: The Exception

Some breakers are listed and marked for 100% continuous operation. These are typically found in commercial panelboards and switchboards from manufacturers like Square D, Eaton, and ABB. When using a 100%-rated breaker, the 125% multiplier does not apply — you size the conductor and OCPD at 100% of the total load. However, the conductor must still be sized for 100% of the continuous load without the 125% bump only if the entire assembly (panel, breaker, and conductor terminations) is listed for 100% operation.

In practice, most residential and light commercial installations use standard 80%-rated breakers, so the 125% rule applies.

Branch Circuit Load Calculation Methods

The NEC provides two approaches for determining branch circuit loads, depending on the load type.

Method 1: Known Load (Specific Equipment)

When you know exactly what the circuit powers, use the equipment’s rated load directly:

Motor loads — Use full-load current (FLC) from NEC Table 430.248 (single-phase) or 430.250 (three-phase), not nameplate current
Fixed appliances — Use nameplate VA or ampere rating (NEC 220.14(A))
HVAC equipment — Use nameplate data per NEC Article 440
EV chargers (EVSE) — Treat as a continuous load at the nameplate rating. A Level 2 charger rated 40A requires conductor and breaker sizing for 40A × 1.25 = 50A

For dedicated circuits serving a single piece of equipment, the calculation is straightforward: take the equipment’s rated current, apply the 125% continuous load multiplier if applicable, and size accordingly.

Method 2: VA per Square Foot (General Lighting and Receptacles)

For general-purpose circuits where you cannot predict the exact connected load, the NEC specifies minimum VA per square foot values in Table 220.12:

Occupancy Type	VA per sq ft
Dwelling units	3*
Office buildings	3.5
Retail stores	3
Warehouses / storage	0.25
Restaurants	2
Hotels / motels (guest rooms)	2
Schools	3
Hospitals	2

*The 2026 NEC reduced the dwelling unit general lighting load from 3 VA/sq ft to 2 VA/sq ft — a significant change that reduces calculated residential service sizes. Verify which NEC edition your AHJ enforces before using either value.

The general lighting VA per square foot includes both lighting outlets and general-use receptacles. You do not add a separate receptacle load on top of the per-square-foot value for these spaces.

Required Branch Circuits for Dwellings

The NEC mandates specific circuits in residential occupancies beyond the general lighting calculation:

Circuit Type	NEC Reference	Minimum VA	Notes
Small appliance (kitchen, dining)	220.52(A)	1,500 VA each, minimum 2 circuits	20A circuits, counted at 1,500 VA each in load calc
Laundry	220.52(B)	1,500 VA	At least one 20A circuit dedicated to laundry area
Bathroom	210.11(C)(3)	N/A (20A circuit)	Dedicated 20A circuit(s) for bathroom receptacles
Garage / outside receptacles	210.11(C)(4)	N/A (20A circuit)	At least one dedicated 20A circuit

These required circuits are included in the overall load calculation at their specified VA values. The small appliance and laundry circuits (totaling at least 4,500 VA for the minimum three circuits) are added to the general lighting load before applying demand factors.

Demand Factors: Why the Panel Doesn’t Need to Handle Every Load at Once

When calculating feeder and service loads, the NEC recognizes that not every circuit operates at full capacity simultaneously. Demand factors reduce the calculated load to reflect realistic usage patterns.

General Lighting Demand Factors (NEC Table 220.42)

Total VA of General Lighting	Demand Factor
First 3,000 VA	100%
3,001 to 120,000 VA	35%
Over 120,000 VA	25%

This means a 2,000 sq ft dwelling with 3 VA/sq ft = 6,000 VA general lighting, plus 4,500 VA small appliance/laundry = 10,500 VA total. After demand factors: first 3,000 VA at 100% + remaining 7,500 VA at 35% = 3,000 + 2,625 = 5,625 VA — a 46% reduction from the connected load.

Fixed Appliance Demand Factor (NEC 220.53)

For four or more fixed appliances (dishwasher, disposal, microwave, water heater, etc.) that are not part of the HVAC or laundry calculation, apply a 75% demand factor to their combined nameplate ratings. This applies to feeder and service calculations only — the individual branch circuit for each appliance is still sized at 100% (or 125% if continuous).

The Optional Method for Dwellings (NEC 220.82)

For existing dwellings or straightforward new construction, NEC 220.82 provides a simplified approach that often yields a smaller service size:

Add up the general lighting load (VA/sq ft × area), small appliance circuits, laundry circuit, and all appliance nameplate ratings
Apply the demand: first 10,000 VA (8,000 VA in some editions) at 100%, remainder at 40%
Add the largest of the HVAC loads (heating or cooling — not both, since they don’t run simultaneously) at 100%

This optional method frequently results in a smaller calculated load than the standard method because the 40% demand factor on everything above 10,000 VA is aggressive. Most AHJs accept either method — use whichever produces the more accurate (not necessarily smaller) result for your installation.

Worked Example: Adding an EV Charger Circuit

You’re adding a Level 2 EVSE to a residential garage. The charger is rated 48A, 240V. The panel is in the basement, 45 feet from the garage.

Step 1: Determine the Load

EVSE at 48A. This is a continuous load per NEC (the charger runs for hours at maximum current).

Step 2: Apply the 125% Continuous Load Rule

48A × 1.25 = 60A minimum for both conductor and OCPD sizing.

Step 3: Select the Breaker

60A is a standard breaker size per NEC 240.6(A). Use a 60A, 2-pole breaker.

Step 4: Size the Conductor

Per NEC Table 310.16 at 75°C: 6 AWG copper = 65A ampacity. 65A ≥ 60A required — 6 AWG passes.

Step 5: Check Voltage Drop

VD = (2 × 12.9 × 48 × 45) / 26,240 = 2.1V

VD% = 2.1 / 240 × 100 = 0.9% — well under 3%. No upsizing needed.

Step 6: Verify Panel Capacity

Does the existing panel have space for a 2-pole 60A breaker? Does the existing service have capacity for the additional 48A (11,520 VA at 240V)? This requires an existing load calculation per NEC 220.83 (or 120.83 in 2026 NEC) to verify the service can handle the addition.

The 2026 NEC added provisions for Power Control Systems (PCS) that can manage EV charging loads dynamically — potentially avoiding a full service upgrade. If the panel is near capacity, investigate PCS options under the 2026 NEC before committing to a $5,000–$30,000 service upgrade.

Worked Example: Commercial Office Lighting Circuit

You’re wiring a 2,400 sq ft office space with LED lighting on 277V circuits. Single-phase, 20A breakers.

Step 1: Calculate the Lighting Load

Office buildings: 3.5 VA/sq ft (NEC Table 220.12)

2,400 sq ft × 3.5 VA = 8,400 VA total lighting load

Step 2: Determine Load per Circuit

At 277V on a 20A breaker: maximum continuous load = 20A × 0.80 = 16A (because commercial lighting is continuous).

Maximum VA per circuit = 277V × 16A = 4,432 VA

Step 3: Calculate Number of Circuits

8,400 VA / 4,432 VA = 1.9 → minimum 2 circuits

In practice, you would likely install 3–4 circuits for better zone control and switching flexibility, even though the NEC only requires 2 circuits minimum for this load. The code sets the floor, not the ceiling.

Load Types That Require Special Calculation Treatment

Not all loads follow the standard calculation method. These common load types have specific NEC rules:

Motor Loads (NEC Article 430)

Motor branch circuit conductors are sized at 125% of the motor FLC (from NEC tables, not nameplate). The OCPD, however, follows a different rule — it’s sized per Table 430.52 at a percentage of the FLC that varies by motor type (typically 250% for standard induction motors with inverse-time breakers). This is not the same as the 125% continuous load rule.

HVAC Equipment (NEC Article 440)

Air conditioning and heat pump equipment uses a Minimum Circuit Ampacity (MCA) and Maximum Overcurrent Protection (MOP) marked on the equipment nameplate. Use MCA for conductor sizing and MOP for breaker sizing — do not perform your own 125% calculation. The manufacturer has already accounted for motor starting current and continuous operation.

Electric Heating (NEC 424)

Fixed electric space heating is always treated as a continuous load. Size conductors and OCPD at 125% of the total heating load. When both heating and cooling loads exist, you typically use only the larger of the two in the service calculation (NEC 220.60) since they are unlikely to operate simultaneously.

Kitchen Equipment in Commercial (NEC 220.56)

Commercial kitchen equipment gets its own demand factor table. For six or more pieces of equipment, the demand factor is 65%. This significantly reduces the calculated feeder load for restaurant kitchens.

How Load Calculations Connect to Wire Sizing

The load calculation gives you the current in amps. From there:

Load current → calculated here
Conductor sizing → NEC Table 310.16, with derating for temperature and conduit fill
Voltage drop check → especially critical for long wire runs where the distance may force a larger conductor
Breaker sizing → NEC 240.4, next standard size per 240.6(A)

The load calculation is step one. If you skip it or estimate loosely, every downstream calculation inherits the error.

Use our electrical load calculator to run through branch circuit and feeder calculations with built-in NEC demand factors — it handles continuous load adjustments and flags when a panel may be near capacity.

Common Load Calculation Mistakes

Applying 125% to non-continuous loads — The multiplier only applies to the continuous portion. A 30A mixed load (20A continuous + 10A non-continuous) needs 20 × 1.25 + 10 = 35A, not 30 × 1.25 = 37.5A.
Treating all residential loads as non-continuous — Electric heat, EV chargers, pool pumps, and some lighting loads are continuous. Undersizing these circuits leads to breaker nuisance tripping after 2–3 hours of operation.
Double-counting receptacle loads — The general lighting VA/sq ft calculation already includes general-use receptacles. Adding a separate receptacle load on top of the per-square-foot value inflates the calculation.
Using demand factors on branch circuits — Demand factors from NEC Table 220.42 apply to feeder and service calculations only. Each individual branch circuit must be sized for its full calculated load.
Forgetting to check panel capacity when adding circuits — A new 60A EV charger circuit may be correctly sized on its own, but if it pushes the total service load beyond the panel’s rating, the service itself needs upgrading. Always verify with an existing load calculation.
Using the wrong NEC edition for VA/sq ft values — The 2026 NEC reduced dwelling general lighting from 3 VA/sq ft to 2 VA/sq ft. Using the old value with a jurisdiction that has adopted 2026 NEC means your service calc is 50% higher than necessary for the lighting component.

The Bottom Line

Every circuit starts with a load calculation. Determine what the circuit powers, classify it as continuous or non-continuous, apply the 125% multiplier where required, and use the NEC’s VA/sq ft tables for general-purpose circuits where the specific load is not known. For feeders and services, demand factors bring the total down to a realistic level — but individual branch circuits must be sized for their full load. Get this number right, and the wire sizing, voltage drop, and breaker selection that follow will all fall into place.