What Wire Gauge Do I Need Based on Amperage and Distance?

Formulas

Voltage drop (single-phase 220V)

ΔV = 2 × L × A × ρ / S

Where:
  ΔV = voltage drop (V)
  L  = cable length (m, one direction)
  A  = amperage (A)
  ρ  = copper resistivity = 0.0178 Ω·mm²/m at 20°C
  S  = conductor cross-section (mm²)
  2  = factor for round-trip current path

For three-phase 380V

ΔV = √3 × L × A × ρ / S

Solving for wire gauge

S = (2 × L × A × ρ) / ΔV_max

Where ΔV_max = V × (maxDropPercent / 100) → for 220V and 3%: ΔV_max = 6.6 V.

Wire ampacity by gauge (AEA 90364)

Residential circuit classifications per AEA

Voltage, amperage, and power

P (W)  = V × A       (single-phase)
P (W)  = √3 × V × A × cos(φ)   (three-phase)
A      = P / V

Residential examples:
  100 W light bulb at 220V  → 0.45 A
  LED TV 150 W              → 0.68 A
  Microwave 1,200 W         → 5.45 A
  Water heater 2,200 W      → 10.0 A
  Electric oven 3,500 W     → 15.9 A
  AC unit 3,000 BTU 1,200W  → 5.45 A
  Electric range 7,000 W    → 31.8 A (very high!)

Why voltage drop matters

Voltage drop is the loss of voltage along the wire due to its electrical resistance. If you have 220V at the panel but only 210V reaches the equipment, that's a 10V drop = 4.5%.

Problems from excessive voltage drop

Maximum allowable drop (AEA standards)

Circuit breaker selection

The circuit breaker (or thermal breaker) protects the wire from overheating. It must satisfy:

A_equipment  ≤  A_breaker  ≤  A_wire_capacity

Example: 15 A equipment, 2.5 mm² wire (21 A capacity) → 16 A breaker (next size above equipment, below wire capacity).

Standard breaker sizes (A): 6, 10, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160.

Differential breaker (RCD/GFCI)

Every residential installation must have a differential breaker of 30 mA (mandatory by AEA). It protects against electrocution by cutting power if current leaks to ground. It does not replace the thermal breaker — they work together.

Wire color codes per AEA

True ground is always green-and-yellow stripe. A wire that's only green or only yellow is not ground.

Wire types

Indicative pricing (Argentina 2026)

Common brands: Imsa, Pirelli, Delcable, Prysmian.

Installation tips

1. Never overload an outlet: avoid power strips for air conditioners or microwaves.
2. Wires in conduit: cables run inside plastic or rigid conduit.
3. No splices inside conduit: splices only in junction boxes.
4. Strict color code: professional electricians always follow AEA colors.
5. Subpanel for large loads: homes over 1,000 sq ft benefit from a second panel near heavy users (kitchen, laundry).
6. Inspect every 5 years: wire insulation degrades; check for loose connections and heat.

Common residential setups

Small house (70 m² / 750 sq ft)

Medium house (150 m² / 1,600 sq ft)

Common mistakes

1. Oversizing for false safety: jumping from 1.5 to 4 mm² is wasteful. Use the AEA table.
2. Ignoring distance: 30 m with 2.5 mm² at 20 A causes over 5% drop (non-compliant).
3. Breaker larger than wire: NEVER. If wire is 2.5 mm² (21 A capacity), max breaker is 20 A.
4. Skipping the differential: not optional — it's a legal and safety requirement.
5. Poor ground connections: most older houses have inadequate grounding. Test with a ground meter.

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