3.4 Continuous Loads, Demand, and 125 Percent Rules

The 125 percent rule is common, not universal

A major journeyman exam trap is treating 125 percent as a magic number that applies everywhere. It appears often because continuous loads stress equipment for a long duration, but the NEC applies it through specific rules. Your job on the exam is to identify the load, identify the rule, and then apply the factor only where required.

A continuous load is generally one where the maximum current is expected to continue for 3 hours or more. Commercial lighting, show-window lighting, some fixed space-heating loads, signs, and certain process loads may be continuous depending on the facts and applicable NEC rule. A garbage disposer or hand dryer is not continuous merely because it is hardwired. Read the question facts.

Basic sizing pattern

A common branch-circuit or feeder pattern is:

Minimum ampacity = noncontinuous load + 125 percent of continuous load

If the continuous load is 16 A and the noncontinuous load is 10 A, the minimum ampacity is:

10 A + (16 A x 1.25) = 10 A + 20 A = 30 A.

Do not multiply the total 26 A by 125 percent unless the rule says all of it is continuous. If you do, you get 32.5 A and may select a larger answer than required. The distinction matters in multiple-choice questions where both answers appear.

Worked example: mixed branch load

A branch circuit supplies a 12 A continuous display lighting load and an 8 A noncontinuous receptacle load. What minimum branch-circuit ampacity is required before choosing conductor size from a table?

Known values: continuous = 12 A, noncontinuous = 8 A.

Required ampacity = 8 + (12 x 1.25) = 8 + 15 = 23 A.

The calculated minimum is 23 A. The next step may involve standard overcurrent device ratings, conductor ampacity, terminal temperature limitations, and small conductor rules. The answer to the arithmetic step is not automatically a 25 A breaker unless the question asks for the next standard rating and the applicable rule allows it.

Demand factor logic

Connected load is the total rating of equipment connected. Calculated load is the load after applying NEC rules such as demand factors, load factors, or specific allowances. Demand factors recognize that not all connected loads operate at full rating at the same time. They are permitted only by specific NEC provisions.

A demand factor is not a field guess. You do not reduce a load because it seems unlikely to run. You reduce it when the NEC table or rule allows reduction for that type of occupancy, equipment, or load group. For dwellings, ranges, dryers, general lighting, multifamily calculations, and other categories may have specific methods. For non-dwelling occupancies, other rules may apply. The correct method depends on the exact article and table in the NEC edition used by your exam.

Order of operations

The exam often tests order. Suppose a problem gives several loads and asks for a feeder. You may need to calculate individual loads, apply demand factors to certain categories, then add continuous-load factors where required, then size conductors and overcurrent protection. Reversing demand and 125 percent can change the answer.

A practical workflow is:

1. List each load and its unit: A, W, VA, kVA, hp, or nameplate.
2. Convert to VA or amperes as required by the rule.
3. Group loads by NEC category: lighting, receptacles, appliances, motors, heating, cooking, dryers, signs, or special equipment.
4. Apply the demand factor only to the load group for which it is allowed.
5. Apply continuous-load sizing where the rule requires it.
6. Convert final VA to amperes if conductor or equipment ampacity is requested.
7. Move to tables or standard-size rules only after the calculated load is established.

Worked example: demand and continuous load

A feeder supplies 18,000 VA of noncontinuous load and 12,000 VA of continuous lighting load on a 240-volt single-phase system. No demand factor is stated or permitted in the question. What minimum feeder ampacity is required?

Continuous adjusted load = 12,000 x 1.25 = 15,000 VA. Add noncontinuous load: 15,000 + 18,000 = 33,000 VA. Convert to amperes: 33,000 / 240 = 137.5 A.

If you first added the loads and divided by voltage, you would get 30,000 / 240 = 125 A, then perhaps multiply all current by 125 percent and get 156.25 A. Both are wrong for this fact pattern. The correct method adjusts only the continuous portion.

Continuous load and equipment ratings

Some listed equipment may be rated for continuous operation at 100 percent under specific conditions. The NEC has provisions that distinguish ordinary equipment from assemblies listed for operation at 100 percent of rating. Do not assume 100 percent operation is allowed unless the problem gives that condition or the code rule supports it. On a contractor/trades exam, the safer method is to follow the stated NEC rule exactly.

Calculator discipline

Keep the continuous and noncontinuous columns separate on scratch work. On PRONTO or computer-based testing, loose paper rules and calculator permissions can vary by delivery method, so practice a compact mental layout you can reproduce with the permitted tools. If a basic four-function calculator is used, avoid long chained entries. Compute the adjusted continuous portion, write or hold it, then add the noncontinuous portion.

Exam traps

Do not apply 125 percent twice. If a load has already been adjusted by a rule or nameplate instruction, read whether the next rule asks for additional sizing. Do not apply demand factors to the 125 percent multiplier itself; demand applies to a load category, while continuous sizing applies to duration and equipment loading. Do not treat demand factor and diversity as the same thing. The NEC provides demand factors; field intuition does not.

Also watch answer wording. Minimum conductor ampacity, minimum branch-circuit rating, calculated load, and overcurrent protective device rating are related but not identical. The question stem tells you which stage of the calculation chain it wants.