Wire AWG Current Carrying Calculator
Wire & Environment
Length & Drop
Key Results
Wire Properties
How to Use the Wire AWG Current Carrying Calculator
Estimate safe continuous current from wire size using a rule-of-thumb current density, then check voltage drop over the run. The tool also applies simple temperature and bundling derates and suggests the next size if limits are exceeded.
1) Pick Wire
- Material – Copper or Aluminum.
- AWG size – gauge number (e.g., 18, 14, 10, 4/0).
- The tool maps AWG → diameter/area using standard relations:
d(mm) = 0.127·92^((36−n)/39),Area = π(d/2)²
2) Environment
- Insulation rating (°C) – e.g., 60/75/90; used for a simple temp derate.
- Ambient (°C) – higher ambient lowers ampacity.
- Current-carrying conductors – number in the bundle; derate above 3.
- Rule-of-thumb J – current density (A/mm²). Start around ~6 A/mm² open air; reduce for tight bundles or warm enclosures.
3) Length & Drop
- Enter one-way length and units (m/ft). Calculator uses round-trip = 2×length.
- Set supply voltage and allowable drop %.
- Resistivity vs temperature is modeled as:
ρ(T) = ρ20·[1 + α·(T − 20 °C)]
4) Load Current
- Enter desired Iload (A) to check voltage drop and losses at that current.
- Tool also computes the max current by drop that still meets your drop %.
5) Read Results
- Ampacity (thermal model): I = J · Area · derates (material, bundle, temperature).
- Max by drop: highest current meeting your drop % across the round-trip length.
- Recommended current: the smaller of ampacity and drop limit.
- Vdrop & Ploss at Iload for heat budgeting.
6) Suggestions
- If Iload > Recommended or drop % is exceeded, the tool suggests the next larger AWG that passes both constraints.
- If none passes, consider parallel runs, shorter lengths, higher system voltage, or lowering J.
7) Limits & Safety
- This is an engineering estimate tool. For code-regulated installs, use official tables (NEC/IS/IEC) and correction factors.
- High ambient, tight conduit, or poor airflow require lower J (more conservative).
- Aluminum needs larger sizes than copper for the same current and terminations rated for Al.
- For AC at high frequency, skin/proximity effects raise resistance—results become optimistic.
Quick Checklist
- Correct material and AWG selected
- Ambient ≤ insulation rating; derate applied
- Bundle count realistic for routing
- J conservative for your enclosure
- Length units correct; round-trip considered
- Drop % meets device spec at Iload
- Recommended current ≥ service current
- Document assumptions in the summary
FAQ & Tips
What J should I start with?
Open-air harnesses often work around 5–7 A/mm². Inside warm boxes or tight bundles, try 2–4 A/mm². High-reliability designs go lower.
Why is length doubled for drop?
Current flows out and back; the loop resistance uses round-trip length.
Copper vs Aluminum?
Aluminum has higher resistivity; the tool applies a material factor and proper ρ(T). Use compatible lugs.
My drop is fine but wire runs warm.
Increase gauge until ampacity margin looks comfortable; drop isn’t the only constraint.
High frequency?
Skin/proximity effects increase AC resistance; for switching currents, consider litz/stranded and check losses experimentally.
Copy-Paste Mini Workflow
1) Choose material (Cu/Al) and AWG
2) Set insulation rating, ambient, bundle count, and J (A/mm²)
3) Enter one-way length, supply V, allowable drop %
4) Enter desired I_load (A)
5) Read: Ampacity, Max by drop, Recommended I, Vdrop, P_loss
6) If limits fail: try next AWG, parallel runs, or adjust J