Calculadora distancia máxima por caída de tensión: AWG/mm², carga y % objetivo

This technical guide explains maximum distance calculations for voltage drop in conductors under load conditions.

Calculations include AWG, mm2, current, acceptable percentage drop, and conductor material corrections for practical installations.

Maximum Cable Length Calculator by Voltage Drop (AWG / mm², Load and Target Drop)

System type Single-phase, 2-wire Three-phase, 3-wire

Nominal voltage (V)

Load current (A)

Allowable voltage drop (%)

Conductor specification AWG (copper) Metric cross-section (mm², copper) Custom loop resistance

Conductor size (AWG) 14 AWG 12 AWG 10 AWG 8 AWG 6 AWG 4 AWG 2 AWG 1 AWG 1/0 AWG 2/0 AWG 3/0 AWG 4/0 AWG

Conductor cross-section (mm²) 1.5 mm² 2.5 mm² 4 mm² 6 mm² 10 mm² 16 mm² 25 mm² 35 mm² 50 mm² 70 mm² 95 mm² 120 mm²

Loop resistance (Ω/m)

Advanced options

Conductor material Copper Aluminium

Operating conductor temperature (°C)

Override voltage drop (V)

You may upload a photo of a nameplate or wiring diagram to suggest typical values for voltage, current and cable size.

📷 Fill inputs from photo AI

⚡ More electrical calculators Reiniciar Copiar Compartir

Enter nominal voltage, load current, conductor specification and allowable voltage drop to obtain the maximum permissible cable length.

🧠 Explain my result 🔍 Review my data

Formulas and calculation method

1. Allowable voltage drop

• From percentage target:
  ΔV_allow (V) = U_nom (V) × (ΔV% / 100)
• If a fixed voltage drop is provided in advanced options:
  ΔV_allow (V) = user-defined value

2. Conductor resistance at operating temperature

• AWG copper table (per conductor):
  R_20 (Ω/m) = tabulated value (Ω/km) / 1000
• Metric copper or aluminium (per conductor, theoretical):
  R_20 (Ω/m) = ρ / A
  where ρ is resistivity (Ω·m) and A is cross-section (m²):
  ρ_copper ≈ 1.724 × 10⁻⁸ Ω·m
  ρ_aluminium ≈ 2.82 × 10⁻⁸ Ω·m
• Temperature correction to operating temperature T (°C):
  R_T (Ω/m) = R_20 × [1 + α × (T − 20)]
  α_copper ≈ 0.00393 1/°C
  α_aluminium ≈ 0.00403 1/°C

3. Voltage drop and maximum one-way length

• Single-phase, 2-wire circuit (line and neutral, same cross-section):
  ΔV (V) = 2 × I (A) × R_T (Ω/m) × L (m)
• Three-phase, 3-wire balanced circuit:
  ΔV (V) = √3 × I (A) × R_T (Ω/m) × L (m)
• Rearranging for maximum one-way length L_max when ΔV = ΔV_allow:
  L_max (m) = ΔV_allow / [k_system × I × R_T]
  where k_system = 2 for single-phase 2-wire, k_system = √3 for three-phase 3-wire.

AWG	Approx. area (mm²)	R_20 (Ω/km, copper)	Metric size (mm²)	R_20 (Ω/km, copper, approx.)
14	2.08	8.29	1.5	≈ 12.1
12	3.31	5.21	2.5	≈ 7.4
10	5.26	3.28	4	≈ 4.6
8	8.37	2.06	6	≈ 3.1
6	13.3	1.30	10	≈ 1.8
4	21.1	0.815	16	≈ 1.2

Technical FAQ for this calculator

Does the calculation include inductive reactance and power factor?

No. For simplicity and robustness, this tool uses the resistive component of the conductor only. This is accurate enough for short to medium low-voltage runs with typical power factors. For long feeders with significant reactance, a full impedance calculation is recommended.

What is the assumed conductor length in the formula: one-way or loop?

The output L_max is the maximum one-way geometric length from source to load. The loop effect (outgoing and return conductors) is included via the factor k_system = 2 for single-phase 2-wire and k_system = √3 for three-phase 3-wire.

How should I choose the allowable voltage drop percentage?

Many installation codes recommend approximately 3% maximum drop on feeders and 5% total (feeder plus final circuit) at full load for low-voltage systems. Sensitive equipment or long feeders may require tighter limits such as 2–3% total.

Can I use this calculator for aluminium conductors?

Yes. Select aluminium in the advanced options. The calculator adjusts resistivity and temperature coefficient accordingly, resulting in a shorter maximum permissible length for the same cross-section compared to copper.

Voltage Drop Fundamentals and Design Objectives

Voltage drop is the reduction in electrical potential along a conductor caused by its impedance under load. The primary design objective is to select conductor cross-section and material so that the voltage at the load remains within acceptable tolerance for safe and efficient operation.

Basic physical relationship

The fundamental linear relationship (resistive approximation) is presented as:

Where:

• I = load current (amperes, A)
• R_total = total series resistance between source and load (ohms, Ω)

Resistance as function of conductor geometry and material

For a straight conductor segment of one-way length L (meters) and cross-sectional area A (mm2), using resistivity at 20 °C:

Common engineering representation (Ω per metre), using resistivity expressed in Ω·mm2/m:

Typically used resistivity values at 20 °C:

• ρ_Cu ≈ 0.017241 Ω·mm2/m (copper)
• ρ_Al ≈ 0.028200 Ω·mm2/m (aluminium)

System configurations and round-trip length

Designers must account for the circuit type when calculating R_total:

• Single-phase line-to-neutral (two-conductor circuit): R_total = 2 × R_segment (out + return)
• DC circuits: R_total = 2 × R_segment (unless separate return path exists)
• Three-phase balanced circuits (line-to-line): for resistive approximation, V_drop_line = √3 × I × R_phase_roundtrip

Formulas for practical use

Single-phase (approximate, resistive):

Three-phase (resistive, line-to-line):

Percent voltage drop:

Temperature correction for conductor resistance

Conductor resistance increases with temperature. Use a linear approximation for most design checks:

Where:

• R_T = resistance at temperature T (°C)
• R_20 = resistance at 20 °C
• α = temperature coefficient at 20 °C (per °C)

Typical α values:

• α_Cu ≈ 0.00393 /°C
• α_Al ≈ 0.0039 /°C

Acceptable voltage drop criteria and standards references

Common practice and regulatory guidance frequently used:

• NEC / NFPA 70: recommends keeping voltage drop to not more than 3% on branch circuits and 5% cumulative for feeder plus branch circuits (informative guidance). See: NFPA.
• IEC 60364 (electrical installations of buildings): contains rules on volt drop and conductor sizing; consult applicable national adoptions. See: IEC.
• IET Wiring Regulations (BS 7671): provides practical limits and methods for voltage drop calculation. See: The IET.
• IEEE standards (e.g., IEEE Std 141 — short-circuit and grounding practices) and manufacturer guidance for voltage-sensitive equipment.

Common conductor sizes, cross-sections and resistances

Below are practical resistance and area values used in international engineering work. Values assume copper or aluminium at 20 °C. Use correction factors for temperature and bundling where necessary.

Notes:

• Resistance values are approximate and rounded to 3 significant figures.
• Aluminium values assume a factor based on ρ_Al ≈ 0.0282 Ω·mm2/m.
• For stranded vs solid conductors, use manufacturer tables for precise resistance.

Step-by-step calculation method

Procedure

1. Identify system voltage (V_system), phase type (single-phase or three-phase), and the allowable percent voltage drop (%allowed).
2. Determine load current I (A) as maximum sustained operating current.
3. Choose conductor material (copper or aluminium) and candidate cross-sectional area A (mm2) or AWG.
4. Obtain R_per_length for selected conductor at 20 °C (Ω/m or Ω/km).
5. Include temperature correction to R if installation ambient temperature deviates significantly from 20 °C.
6. Compute R_total for round-trip length (single-phase: 2 × R_segment; three-phase: use √3 factor as appropriate).
7. Compute V_drop and %V_drop. Compare with %allowed. If %V_drop > %allowed, increase conductor size or reduce length.

Worked formula summary

Single-phase maximum permissible one-way length L_max (m) for a chosen A given %allowed and I:

Three-phase approximate (resistive):

Example calculations (realistic cases)

Two complete worked examples follow: one single-phase residential feeder and one three-phase industrial feeder.

Example 1 — Single-phase residential: circuit lighting and sockets

Given:

• System voltage V_system = 230 V (line-to-neutral)
• Maximum continuous load I = 16 A (typical ring or radial circuit)
• Conductor material = copper
• Target maximum voltage drop = 3% (single-phase branch circuit limit)
• Selected conductor area = 2.5 mm² (common for lighting/sockets in many countries)
• One-way cable length unknown; compute maximum allowable one-way length L_max.

Step 1 — determine allowable V_drop:

Step 2 — compute R_per_m for copper 2.5 mm²:

Compute numeric values:

L_max = 6.9 V / (16 A × 2 × 0.0068964 Ω/m) = 6.9 / (16 × 0.0137928) = 6.9 / 0.220685 = 31.27 m

Result:

• Maximum one-way length ≈ 31 m using copper 2.5 mm² to remain within 3% voltage drop at 16 A.

Considerations:

• If the ambient temperature is high, apply R_T correction: e.g., 40 °C => factor = 1 + 0.00393 × (40 − 20) ≈ 1.0786. Effective R increases ~7.9% and L_max decreases proportionally.
• If the circuit is three-core or in conduit with multiple circuits, derate for thermal effects and use manufacturer/standards tables.

Example 2 — Three-phase motor feeder (industrial)

Given:

• System voltage V_system = 400 V (line-to-line three-phase)
• Continuous load current I = 200 A
• Conductor material = aluminium
• Target maximum percent voltage drop = 3% (system-level constraint)
• Selected conductor area candidates: 70 mm² and 95 mm² aluminium
• One-way length L = 150 m (known distance from transformer to motor)

Step 1 — allowable V_drop:

Step 2 — compute R_per_m for aluminium:

Using R_per_km ≈ 28.2 / A(mm²)

For 70 mm²:

V_drop = 1.732 × 200 × 0.0004029 × 150 = 1.732 × 200 × 0.060435 = 1.732 × 12.087 = 20.93 V

For 95 mm²:

V_drop = 1.732 × 200 × 0.0002968 × 150 = 1.732 × 200 × 0.04452 = 1.732 × 8.904 = 15.42 V

Interpretation:

• 70 mm² aluminium yields ~5.23% drop — exceeds 3% target; may be unacceptable for sensitive equipment.
• 95 mm² aluminium yields ~3.85% drop — still above 3% but closer; to achieve 3% either increase cross-section further or accept higher allowed drop if standards permit.
• Calculate required area by rearranging formula for L_max or A_req. For three-phase, approximate required R_per_m to meet 3%:

R_required = V_drop_allowed / (√3 × I × L) = 12 / (1.732 × 200 × 150) = 12 / (51,960) = 0.0002310 Ω/m

Result:

• Approximately 120–125 mm² aluminium conductor required to meet 3% target for 200 A at 150 m one-way.

Practical considerations beyond pure voltage drop

• Current-carrying capacity: conductor size must also meet ampacity requirements per standards (NEC, IEC, BS). Often a larger size is chosen to satisfy both ampacity and voltage drop.
• Short-circuit rating and protective device coordination: ensure conductor sizing satisfies fault current withstand, protection settings, and thermal damage criteria.
• Installation conditions: grouping, ambient temperature, soil thermal resistivity (for buried cables), and ventilation impact conductor resistance and ampacity.
• Reactive components: motors and long cables introduce inductance; when X is significant, use complex impedance Z and use V_drop = I × |Z| and compute using phasors or conservative approximate multipliers.
• AC skin and proximity effects: for very large conductors or high frequencies, use conductor correction factors or manufacturer impedance data.
• Voltage rise for distributed generation: design must consider reverse power flow and voltage rise limits from distributed generation sources.

Formulas for AC circuits including reactance (practical engineering)

When inductive reactance is non-negligible, use complex form:

Line voltage drop (single-phase AC, phasor magnitude):

For three-phase:

Where X can be approximated from cable data (Ω/km). Use manufacturer impedance tables at a given frequency (50/60 Hz) for accuracy.

Additional tables for quick lookup (typical maximum circuit lengths for 3% drop)

Assumptions: copper conductors, single-phase, continuous current at listed values, and 3% allowable voltage drop at 230 V.

Note: Table values rounded and intended for initial sizing only. Always verify with full calculations and local rules.

Checklist for final design verification

1. Verify ampacity with applicable code taking temperature, grouping, and insulation into account.
2. Calculate voltage drop for worst-case continuous load and ensure it meets system requirements.
3. Consider short-circuit conditions and protective device coordination (minimum conductor size to withstand fault energy).
4. Consult cable manufacturer impedance/thermal data for long runs or large sizes.
5. Document assumptions: ambient temperature, conductor material, method of laying, and target % voltage drop.

Regulatory references and authoritative resources

• NFPA 70 — National Electrical Code (NEC). See full text and commentary: https://www.nfpa.org/NEC
• IEC 60364 series — International Electrotechnical Commission standard for electrical installations: https://www.iec.ch/
• BS 7671 Requirements for Electrical Installations (IET Wiring Regulations): https://www.theiet.org/
• IEEE Std 141 (Red Book) — grounding and power distribution: https://standards.ieee.org/
• Manufacturers’ cable datasheets (e.g., Nexans, Prysmian) for precise conductor resistance and impedance tables.

Where national regulations or utility requirements specify different voltage drop limits, those mandatory limits take precedence. Always cross-check with local codes and the equipment manufacturer recommendations.

Summary of best practices for SEO-targeted technical documentation

• Provide clear formulas with variable definitions and typical values to assist designers and engineers.
• Include lookup tables for common conductor sizes and materials to accelerate preliminary sizing.
• Provide worked examples with numeric steps to illustrate practical application and verification methods.
• Reference authoritative standards and link to source documents to support compliance and credibility.

For any specific project, perform a detailed analysis including temperature corrections, reactive components, and coordination with local regulations. Use this document as a technical methodology for calculating maximum permissible distance by allowable voltage drop considering AWG, mm², load current, and design objective.