Long Run Voltage Drop Calculator

Purpose and model boundary

Derives AWG cross-section and temperature-adjusted conductor resistance, evaluates single-phase, balanced three-phase, or DC runs, and computes every editable conductor candidate against ampacity, running-drop, starting-drop, and cost criteria.

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

• system type: a listed route or text value.
• load input route: a listed route or text value.
• selection objective: a listed route or text value.
• continuous load: a listed route or text value.
• check starting drop: a listed route or text value.
• source voltage v: entered in V.
• one way length ft: entered in ft.
• operating current input a: entered in A.
• apparent power kva: entered in kVA.
• real power kw: entered in kW.
• motor horsepower: entered in hp.
• motor efficiency: entered in fraction.
• power factor: entered in fraction.
• starting current multiplier: entered in times operating current.
• conductor temperature c: entered in deg C.
• upstream drop percent: entered in fraction of source voltage.
• branch drop target percent: entered in fraction of source voltage.
• total drop target percent: entered in fraction of source voltage.
• starting drop target percent: entered in fraction of source voltage.
• connection count: entered in connections.
• connection resistance mohm: entered in mOhm.
• annual operating hours: entered in h/year.
• energy rate per kwh: entered in user currency/kWh.

The candidate grid contains 10 fixed data rows plus one header row with these columns: Candidate label, Include, AWG code (AWG code), Material, Product ampacity (A), Reactance (ohm/kft), Resistance multiplier (fraction), Installed conductors (conductors), Unit cost (user currency/ft), Fixed cost (user currency). Numeric columns retain the units shown here; text, route, and include columns are intentionally unitless.

Governing relationships

The active route converts entered current, kVA, kW, or motor horsepower to operating current I_op (A). Design current is:

I_design = I_op

or, for a continuous load:

I_design = 1.25 I_op

When the starting-drop check is active, starting current is:

I_start = I_op M_start

M_start is the entered multiplier.

For candidate j, AWG diameter and area are:

d_j = 0.127 * 92^((36-g_j)/39)

A_j = pi d_j^2/4

d_j is in mm and A_j is in mm^2. Resistance at 20 C and at conductor temperature are:

R_20,j = rho_j 304.8 m_R,j / A_j

R_T,j = R_20,j[1+alpha_j(T-20)]

R_20,j is in ohm/kft. rho_j is 0.017241 ohm-mm^2/m for copper or 0.028264 for aluminium, m_R,j is the entered resistance multiplier, alpha_j is the material temperature coefficient (1/deg C), and T is deg C.

Running drop is:

DeltaV_j = I_op[k_phase L_kft(R_T,j PF + X_j sqrt(1-PF^2)) + R_conn]

DeltaV_j is in volts. k_phase is 2 for single-phase/DC or sqrt(3) for three-phase, L_kft is one-way length (kft), X_j is reactance (ohm/kft), and R_conn is total entered connection resistance (ohm). Drop fraction is:

delta_j = DeltaV_j/V_source

Resistive annual loss is:

E_loss,j = I_op^2 k_loss L_kft R_T,j h_year / 1000

E_loss,j is in kWh, k_loss is 2 or 3 conductors, and h_year is operating hours. Only candidates passing ampacity and every active drop gate are ranked.

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

• operating current a (A): Operating current entered or derived through the selected load route.
• design ampacity a (A): Operating current multiplied by 125 percent only when the continuous-load selector is active.
• recommended candidate: Passing candidate selected by the active cost, area, or voltage-drop objective.
• recommended area mm2 (mm^2): Geometrically derived solid-equivalent AWG cross-section of the selected candidate.
• running drop v (V): Approximate current-path drop at operating current for the selected candidate.
• running drop percent (fraction of source voltage): Selected branch drop divided by nominal source voltage.
• total running drop percent (fraction of source voltage): Selected branch drop plus the entered upstream drop.
• load end voltage v (V): Nominal source voltage less selected running voltage drop.
• estimated conductor cost (user currency): Installed conductor length times editable unit cost plus editable fixed cost.

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 conductors, ratings, costs, and operating values are synthetic illustrative demonstrations and must be replaced with project evidence.

• One-way length is entered; voltage drop uses factor two for single-phase and two-wire DC or square-root-three for balanced three-phase, while conductor loss sums two current paths or three balanced phase conductors respectively.

• Grid ampacity, reactance, price, stranding multiplier, and installed conductor count are synthetic editable planning inputs, not code tables or product claims.

• Copper and aluminum resistivity and temperature coefficients are disclosed public engineering constants; actual product resistance prevails.

• Continuous-load adjustment affects the ampacity gate; voltage drop uses operating current and the optional start scenario uses the entered current multiplier.

• The branch and upstream targets are planning thresholds and remain editable for the locally adopted requirements and equipment needs.

• Voltage-drop arithmetic is not conductor ampacity, overcurrent protection, fault-current, grounding, bonding, raceway-fill, insulation-temperature, terminal, neutral, harmonic, or motor-branch-circuit design.

• The approximate AC equation does not solve an unbalanced multiphase network, nonlinear load, skin effect, proximity effect, or source-impedance model.

• A licensed electrician or electrical engineer must select equipment and conductors to the locally adopted rules, listing instructions, utility requirements, and authority having jurisdiction.

• Cost excludes trenching, conduit, pull difficulty, splices, equipment, permits, labor, and project-specific escalation unless represented in the editable fixed cost.

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 162 saved test cases, covering both calculated results and entries that should be refused, run against this exact workbook.

• NIST Circular 31, Copper Wire Tables - Primary public source for the American Wire Gauge geometric progression and gauge-number convention. Official public U.S. government publication; the general equation is independently implemented and no table or prose is copied or reproduced.
• NIST Handbook 100, Copper Wire Tables - Primary public source for annealed-copper resistivity, temperature coefficient, and resistance arithmetic. Official public U.S. government publication; necessary constants are independently implemented and no table or prose is copied or reproduced.
• NIST Handbook 109, Aluminum Wire Tables - Primary public source for EC-H19 aluminum resistivity, temperature coefficient, and resistance arithmetic. Official public U.S. government publication; necessary constants are independently implemented and no table or prose is copied or reproduced.
• Seattle Public Utilities Electrical Design Calculations - Official municipal engineering source for the approximate AC voltage-drop relationship and single- versus three-phase factors. Official public municipal engineering guidance; the general equation is independently implemented and no table or prose is copied or reproduced.
• NFPA 70 branch-circuit development record - Official standards-development record for clause context, continuous-load treatment, and informational voltage-drop targets cited only in References and Disclaimer. Clause names and public-development context only; no licensed code table or prose is embedded.

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.