Wire Sizing Calculator

Code-aware calculator with cost analysis, educational tooltips, and real-world examples for DIY solar installers in Canada.

✓ Calculations based on CEC 2024 & NEC 2023 standards | Last updated: Feb 2026

📊 Quick Reference - Common Solar Wire Sizes

10 AWG
30A Max
Charge Controllers
8 AWG
40A Max
Inverter DC Input
4 AWG
70A Max
Battery Banks
2 AWG
95A Max
Main DC Bus

⚡ Interactive Wiring Diagram — Click Any Wire or Component

Not sure which part of your system you're sizing? Click any wire or component in the diagram below — we'll explain what it does, pre-fill the calculator with typical values, and show you the right product to buy.

👆 Tap any highlighted zone to explore

© offgridsolarsystem.ca — Interactive diagram. All rights reserved.

DC (2-wire) or AC (2-wire line-neutral).
Nominal operating voltage.
Continuous load current (used for 125% OCPD rule).
Source to load, in metres. Used for round-trip voltage drop.

💡 Common Off-Grid Application Examples

Solar Panel to Charge Controller (48V, 10A, 15m)
8 AWG
Battery Bank to Inverter (24V, 150A, 1.5m)
2/0 AWG
Subpanel Feeder (120V AC, 30A, 30m)
8 AWG

💡 Pro Tips for Wire Selection

1. Always Size Up: When in doubt between two wire sizes, choose the larger. The cost difference is minimal compared to the risk of undersizing.
2. Check Both Calculations: Your final wire size must satisfy BOTH ampacity (heat) and voltage drop (efficiency) requirements. Always use the larger result.
3. Consider Future Expansion: If you might add panels or batteries later, size wire for future capacity now. Replacing wire is expensive and disruptive.
4. Temperature Matters: Roof-mounted conduit can reach 70°C+ in summer. Always use worst-case ambient temperature for calculations.
5. Use Quality Connectors: Proper crimped connections are critical. Poor connections cause 80% of solar system failures. Invest in quality terminals and crimping tools.

📊 Wire Gauge Quick Reference

AWG Max Amps Cu
(75°C)		 Max Amps Al
(75°C)		 Diameter
(mm)		 Common Use
14 20A 15A 1.6mm Lighting circuits
12 25A 20A 2.0mm General outlets
10 35A 30A 2.6mm Small charge controllers Shop 10 AWG →
8 50A 40A 3.3mm Medium solar arrays Shop 8 AWG →
6 65A 50A 4.1mm Large charge controllers Shop 6 AWG →
4 85A 65A 5.2mm Battery banks (short runs) Shop 4 AWG →
2 115A 95A 6.5mm Inverter DC input Shop 2 AWG →
2/0 175A 145A 9.3mm Large battery banks Shop 2/0 →

🛒 Wire Buying Guide — Shop the Right Gauge on Amazon.ca

Once your calculator result shows the recommended AWG, use this guide to find the right product.

As an Amazon Associate, we earn from qualifying purchases. All products are independently selected based on suitability for Canadian off-grid solar installations.

💡 Smart Buying Tip: Always buy 10–15% more wire than your calculated run length! Measurement errors, routing around unexpected obstacles, and re-terminating crimps happen to everyone. Ordering a second small spool later wastes time and adds extra shipping fees. Buy extra upfront.

All options below ship Prime to Canada.

☀️ Solar Panel Wire (PV/USE-2 Rated)

For panel-to-charge-controller and panel-to-combiner-box runs. Must be UV-resistant, rated for wet locations, and sunlight-resistant. USE-2 or PV-rated wire is required by CEC Section 64 for outdoor solar applications.

10 AWG Solar Wire (30A max · Charge controller circuits)

Best for: Panel strings to MPPT/PWM charge controllers up to 30A. Look for tinned copper, dual-insulated, 10 AWG USE-2/PV wire.

Shop 10 AWG Solar Wire on Amazon →

8 AWG Solar Wire (40A max · Medium arrays · Longer runs)

Best for: Arrays over 400W or runs over 5 metres where voltage drop requires a step up from 10 AWG.

Shop 8 AWG Solar Wire on Amazon →

6 AWG Solar Wire (55A max · Large arrays · Long runs)

Best for: High-current panel strings (over 40A), long cable runs over 10 metres, or 48V systems with large arrays.

Shop 6 AWG Solar Wire on Amazon →

🔋 Battery Bank Cables (Welding Cable)

Battery connections carry your system's highest currents. Welding cable is the preferred choice: it's highly flexible in cold Canadian weather and handles high current surges efficiently.

4 AWG Welding Cable (70A max · Small battery banks)

Best for: Small 12V or 24V systems up to 800W inverters. Ideal for battery-to-busbar connections.

Shop 4 AWG Welding Cable →

2 AWG Welding Cable (95A max · Most common battery gauge)

Best for: 24V systems up to 2000W inverters and 48V systems up to 4000W. The classic off-grid cabin standard.

Shop 2 AWG Welding Cable →

2/0 AWG Welding Cable (130A+ max · Large inverters)

Best for: 48V systems with 3000W+ heavy duty inverters and massive LiFePO4 battery banks.

Shop 2/0 AWG Welding Cable →

🔌 Connectors & Accessories

Every solar installation needs these. Buy them alongside your main wire spools to keep delivery configurations simple.

MC4 Connector Kit

Required for every single solar panel termination. Always buy IP67 waterproof-rated configurations.

Shop MC4 Connector Kit →

Copper Ring Terminal Lugs

For heavy battery terminal hookups. Fits 2 AWG and 4 AWG configurations perfectly with standard M8 terminal ports.

Shop Ring Terminal Lugs →

MC4 Inline Fuse Holder (30A)

Critical string protection needed to comply with safety layouts between your arrays and charge controllers.

Shop MC4 Inline Fuse Holder →

Adhesive-Lined Heat Shrink Tubing

Dual-wall assortments to trap out moisture completely. Crucial step for cold weather exposures across Canada.

Shop Heat Shrink Tubing →

How Wire Sizing Works

Proper wire sizing in off-grid solar systems is critical for two main reasons: safety and efficiency. When electricity flows through wire, it encounters resistance, which causes voltage drop and heat generation.

Voltage Drop

As electricity travels through wire, some voltage is "lost" due to the wire's resistance. This lost voltage reduces the power available to your equipment and can cause poor performance. In solar systems, excessive voltage drop means you're not getting the full power from your panels or batteries.

Ampacity (Current Capacity)

Every wire size has a maximum safe current capacity called ampacity. Exceeding this limit causes dangerous overheating, which can melt insulation, start fires, or damage equipment. The National Electrical Code (NEC) provides ampacity ratings for different wire types and installation conditions.

Safety Factors

Off-grid solar systems require additional safety considerations. Both the Canadian Electrical Code (CEC) and US National Electrical Code (NEC) mandate that continuous loads (running for 3+ hours) must not exceed 80% of the circuit's rated capacity. This is why we apply the 125% rule - multiply your continuous current by 1.25 when sizing wire and breakers.

Important: Undersized wire is a leading cause of electrical fires in solar installations. Always err on the side of larger wire when in doubt. Check with your local electrical inspector for specific requirements in your province.

Formulas & Calculations

Voltage Drop Calculation (DC)

The basic formula for calculating voltage drop in DC circuits:

Voltage Drop (V) = (2 × K × I × L) / A Where: • K = Resistivity constant (12.9 for copper, 21.2 for aluminum) • I = Current in amperes • L = One-way distance in feet (metres × 3.28084) • A = Wire cross-sectional area in circular mils
Why multiply by 2? Because current must travel to the load AND back, creating a round-trip that doubles the resistance.

Voltage Drop Calculation (AC)

Voltage Drop (V) = (2 × K × I × L × PF) / A Power Factor (PF) accounts for the phase difference between voltage and current in AC circuits with inductive or capacitive loads. Use PF = 1.0 for purely resistive loads (heaters, incandescent lights).

Percentage Voltage Drop

Voltage Drop (%) = (Voltage Drop ÷ System Voltage) × 100

Wire Size (Circular Mils) Calculation

To find the minimum wire size needed:

A = (2 × K × I × L) ÷ (System Voltage × Max Voltage Drop %)

CEC 125% Continuous Load Rule

Design Current = Actual Continuous Current × 1.25
Example: A charge controller drawing 40A continuously requires wire sized for 40 × 1.25 = 50A minimum.

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Frequently Asked Questions

Q: Can I use smaller wire for short cable runs?
A: Not necessarily. While voltage drop may be acceptable on short runs, you must still meet ampacity requirements. A 100A current requires appropriately sized wire regardless of distance. Always check both voltage drop AND ampacity calculations.
Q: What happens if I use wire that's too small?
A: Undersized wire creates two major problems: dangerous overheating (fire risk) and excessive voltage drop (poor system performance). Your equipment may not function properly, batteries won't charge efficiently, and you risk electrical fires.
Q: How do battery bank cables differ from solar panel wiring?
A: Battery cables typically carry much higher currents (50-200A+) and require larger wire sizes (2 AWG to 4/0 AWG). Solar panel wiring usually carries lower currents (10-40A) but may span longer distances. Battery cables should be kept as short as possible and use welding cable for flexibility.
Q: What's the difference between THWN, USE-2, and welding cable?
A: THWN: Building wire, good for conduit runs and AC circuits. USE-2: Solar-rated cable, UV resistant, perfect for outdoor DC solar wiring. Welding Cable: Extremely flexible, ideal for battery connections but not outdoor rated without protection.
Q: Should I always follow the 3% voltage drop rule?
A: The 3% rule is a good general guideline, but you can be more flexible: 2% for critical loads (medical equipment), up to 5% for non-critical loads (lighting). In low-voltage systems (12V), even 3% can cause noticeable performance issues.
Q: Is it worth upgrading to larger wire than calculated?
A: Often yes! Slightly larger wire costs little extra but provides: lower voltage drop (better efficiency), cooler operation (longer life), future expansion capability, and greater safety margin. It's cheap insurance for your system.
Q: Can I splice or extend solar cables?
A: Yes, but use proper MC4 connectors for solar panel connections. For DC circuits, use appropriate splice boxes or junction blocks. Never use wire nuts in DC solar applications - they can fail over time due to thermal cycling.
Q: What about temperature derating for wire ampacity in Canadian climates?
A: Canadian installations face unique challenges - from extreme cold to hot summers. Wire ampacity decreases in hot conditions but cold weather can make cables brittle. If cables run through hot attics, direct sun, or are bundled together, you must apply CEC derating factors. High-temperature locations may require wire sized 20-30% larger than standard calculations.

References & Standards

Canadian Electrical Code (CEC)

US National Electrical Code (NEC) - For Reference

Canadian Standards & Certifications

📊 Calculation Standards: Wire sizing formulas follow Canadian Electrical Code (CEC) Section 4 ampacity tables and Section 64 solar PV requirements. Aluminum ampacity set at 84% of copper per CEC Table 2. Bundling derating applies at 4+ conductors per CEC/NEC. AC voltage drop includes power factor correction. Distance inputs in metres. Last updated: February 2026.
Important Disclaimer: This calculator uses principles common to both Canadian (CEC) and US (NEC) electrical codes. While wire sizing fundamentals are similar, always consult with a licensed electrician and your provincial electrical authority for final approval. Each province may have specific amendments to the CEC, and local requirements can differ. Contact your local electrical inspector before beginning any solar installation.