Demand Factor Estimate (NEC 220 Context)

A connected load figure by itself overstates the load a service or feeder will actually carry. Not every VA of connected equipment operates simultaneously at full output, so raw nameplate totals produce oversized conductor and overcurrent device selections if used directly. The Demand Factor Estimate calculator takes a connected load and applies user-defined block factors to produce an estimated demand VA figure — the number that feeds into preliminary conductor ampacity selection, feeder sizing discussions, and load-side equipment review before a full code-based load calculation is performed.

In the reference case, a connected load of 50,000 VA is split into a first-block load of 3,000 VA at a first-block factor of 100%, and a second user-defined block of 47,000 VA at a remaining-block factor of 50%. The result is an estimated demand from entered blocks of 26,500 VA — roughly half the connected load — which is the figure a designer would carry forward into conductor sizing rather than the full 50,000 VA nameplate total.

Inputs and What They Represent

The calculator accepts five entry fields:

• Connected load (VA) — the total nameplate or calculated load before any demand factor is applied.
• First-block load (VA) — the portion of connected load assigned to the first demand tier, typically the tier most likely to run near full capacity.
• First-block factor (%) — the percentage of the first-block load counted toward demand.
• Second user-defined block (VA) — the remaining portion of load assigned to a second tier, usually the larger, more diversified portion of the load.
• Remaining-block factor (%) — the percentage of the second block counted toward demand.
• Fixed allowance (VA) — an optional flat VA addition applied directly to the demand total, independent of either block.

These fields do not correspond to any single fixed NEC table. They are generic block-and-factor inputs that let a user model any two-tier demand structure — whether drawn from a dwelling-unit table, a commercial lighting demand schedule, or an internal engineering estimate — without the calculator hardcoding a specific code table.

Formula Behavior

The calculator runs six linked calculations:

Applied first-block VA = first-block VA × first-block factor % / 100 Applied remaining-block VA = remaining-block VA × remaining-block factor % / 100 Estimated demand VA = fixed allowance VA + applied first-block VA + applied remaining-block VA Total defined block VA = first-block VA + remaining-block VA Unmodeled connected load VA = connected load VA − first-block VA − remaining-block VA Diversity allowance VA = connected load VA − estimated demand VA

A seventh figure, effective demand factor %, is derived as estimated demand VA ÷ connected load VA × 100, giving a single percentage that summarizes how much diversity credit the block structure produced relative to the full connected load.

Calculation Example

Using the reference inputs — 50,000 VA connected load, first block 3,000 VA at 100%, remaining block 47,000 VA at 50%, fixed allowance 0 VA:

Field	Value
Applied first-block demand	3,000 VA
Applied remaining-block demand	23,500 VA
Total defined load blocks	50,000 VA
Unmodeled connected load	0 VA
Estimated demand from entered blocks	26,500 VA
Diversity allowance from entered blocks	23,500 VA
Effective demand factor	53%

Because the two blocks (3,000 + 47,000 = 50,000 VA) equal the full connected load, unmodeled connected load is 0 VA. If a user enters block totals that fall short of the connected load figure, that field reports the gap — VA that has not been assigned a demand factor and is excluded from the estimated demand result. That gap must be resolved manually; the calculator will not distribute it automatically or apply a default factor to it.

Where the Output Is Used

The estimated demand VA result is the starting point for downstream feeder and service work: conductor ampacity selection, overcurrent protective device sizing, panel schedule load entries, and voltage-drop review at the estimated operating current rather than the full connected-load current. The diversity allowance VA figure — 23,500 VA in the example — quantifies how much load capacity is being deferred to diversity rather than continuous simultaneous operation, which is useful when documenting load calculations for an AHJ review or comparing design margin against actual measured demand from utility or monitoring data.

Code and Field Limitations

This calculator performs arithmetic on user-supplied blocks and factors. It does not reproduce any NEC dwelling-unit demand table, does not apply Article 220 load calculation methods automatically, and does not select factors on the reader’s behalf. NEC 220 is referenced here as legacy and topical context only; current load-calculation numbering — including any Article 120/220 renumbering — must be confirmed against the code edition adopted by the local AHJ before a demand factor derived from this tool is used in a submitted load calculation.

The first-block and remaining-block structure models a simple two-tier demand schedule. It does not handle multi-tier tables, motor load additions with separate demand rules, continuous-duty multipliers, or receptacle/lighting load categories that carry distinct demand treatment under an adopted code. Any of those conditions require a calculation method specific to the governing code section, performed separately from this estimate. Verify final conductor and overcurrent device selections against the adopted code edition and local amendments before construction.