Circuit Load Panel Capacity Calculator

Purpose and model boundary

Builds a fixed split-phase circuit schedule, separates continuous and noncontinuous current, applies a transparent 125 percent planning multiplier, routes each load to the correct panel leg, and reports the binding spare-capacity result.

Do not treat this result as an electrical design, code-compliance determination, permit approval, utility commitment, equipment approval, safety certification, cost quote, or endorsement by a cited source. Service data, panel ratings, conductor properties, equipment loads, route lengths, manufacturer instructions, utility requirements, locally adopted codes, and approval thresholds remain the user's responsibility.

Inputs and units

• existing load basis: a listed route or text value.
• line to line voltage: entered in V.
• service rating: entered in A per leg.
• external leg a current: entered in A.
• external leg b current: entered in A.
• imbalance check threshold: entered in fraction of service rating.

The circuit grid contains 12 fixed data rows plus one header row with these columns: Include, Circuit label, Stage, Connection, Input basis, Noncontinuous value (selected input basis), Continuous value (selected input basis), Power factor (fraction), Planning demand factor (fraction), Installed breaker (A), Source note. Numeric columns retain the units shown here; text, route, and include columns are intentionally unitless.

Governing relationships

For circuit row r, the workbook converts the selected input basis to noncontinuous current I_nc,r (A) and continuous current I_c,r (A), then applies:

I_min,r = I_nc,r + 1.25 I_c,r

The row apparent load is:

S_r = V_r I_r

for a current basis, or:

S_r = P_r / PF_r

for a real-power basis. V_r is the active 120 V or 240 V connection voltage, I_r is route current in A, P_r is real power in W, and PF_r is the entered power factor (fraction).

After the row planning-demand factor is applied, 240 V load is placed on both legs and 120 V load is placed on its selected leg. The reported reconciliation is:

S_total = (I_A + I_B) V_LL / 2

I_A and I_B are projected leg currents (A), and V_LL is line-to-line voltage (V). Maximum utilization, spare current, and leg imbalance are:

U = max(I_A,I_B) / I_service

I_spare = min(I_service-I_A, I_service-I_B)

B = abs(I_A-I_B) / I_service

I_service is the entered per-leg service or panel rating (A), and I_spare is in amperes.

Calculation sequence

1. Validate every active selector, scalar bound, type, and every fixed-grid entry.
2. Apply the selected route and ignore values from inactive fields.
3. Normalize unit-dependent inputs into the workbook's calculation basis.
4. Evaluate every included row or candidate and aggregate the active schedule.
5. Calculate primary and supporting outputs, populate the authored chart series, and apply derived numeric checks.
6. Return the workbook status with the computed results; invalid input is never converted into a plausible engineering answer.

Outputs and interpretation

• projected leg a current (A): Existing leg-A basis plus all included proposed rows routed to leg A.
• projected leg b current (A): Existing leg-B basis plus all included proposed rows routed to leg B.
• maximum leg utilization (fraction of rating): Larger projected leg current divided by the panel or service rating.
• 240v spare capacity (VA): Smaller remaining leg-current margin times line-to-line voltage; zero when either leg is overloaded.

The chart is an explanatory view of the workbook's named chart ranges. It does not add a separate calculation or replace the numeric outputs.

Validation and status logic

The workbook evaluates Model_Status in the order shown. The first matching condition wins.

Assumptions and limitations

• All shipped/default engineering values and circuit rows are synthetic illustrative demonstrations and must be replaced with project-specific verified inputs.

• The service is modeled as a single-phase split-phase system; 120-volt loads occupy one leg and line-to-line loads occupy both legs.

• The 1.25 continuous-load multiplier is explicit and not editable; any user demand factor is a planning assumption that requires a documented local basis.

• External leg demand is assumed to have already been adjusted or approved by the user's electrician, utility, engineer, or authority having jurisdiction.

• All twelve grid rows are sent complete; inactive rows are explicit typed fillers and contribute zero.

• This is not an Article 220 service calculation, load study, permit document, fault-current study, conductor-ampacity check, or code-compliance determination.

• Breaker-handle totals are not used as service demand. The model does not apply dwelling demand tables, appliance demand factors, neutral calculations, feeder/service conductor sizing, temperature/termination limits, correction factors, or local amendments.

• A licensed electrician or engineer and the local authority having jurisdiction must verify the adopted code edition, panel and service ratings, measured demand basis, load diversity, leg allocation, equipment compatibility, and installation.

Restrictions and non-computing states

Each numeric control offers a working range chosen for usable entry, which is not always the limit this calculator enforces; a value outside that limit is rejected with a message rather than quietly accepted. The calculator additionally enforces allowed choices, active-field types, complete fixed-grid rows, and conditional or cross-field rules before computing.

Unsupported route values, incomplete rows, out-of-domain inputs, relational failures, nonfinite derived arithmetic, and workbook error tokens are non-computing states. Hidden inputs remain in the values sent to the calculator but must not affect results while those fields are inactive.

Errors and warnings

A rejected entry means the submitted state failed the published input rules. Workbook NOT VALID identifies an invalid active domain or unsupported derived arithmetic. Workbook CHECK retains a finite result while flagging a planning condition that needs review. OK means only that the delivered workbook logic closed within the entered assumptions; it is not code compliance, professional approval, or a safety guarantee.

This version is checked against 52 saved test cases, covering both calculated results and entries that should be refused, run against this exact workbook.

• NFPA 70, National Electrical Code, current edition index - Authoritative current-edition pointer; users must identify the edition and amendments locally adopted for their project. Official NFPA publication index; no code table or copyrighted standard text is embedded.
• NFPA public record for branch-circuit conductor and continuous-load arithmetic - Public technical record supporting the 125 percent continuous-load relationship and informational voltage-drop context. Official NFPA standards-development record; the workbook cites clauses and independently implements arithmetic without reproducing tables.

Licensing conclusion: No licensed, proprietary, manufacturer, utility, product-price, code-table, forecast, or external dataset is embedded. The calculator independently implements general engineering arithmetic from cited public and official sources; all defaults, labels, conductor/load rows, equipment assumptions, diagrams, and test values are synthetic illustrations. No NFPA table, utility tariff, breaker catalog, conductor ampacity, or proprietary panel data is reproduced; demand factors and examples are synthetic and editable.