A solar cable must safely carry continuous DC current outdoors for many years while limiting voltage drop and resisting heat, UV, moisture and mechanical damage. Connectors are equally important: mismatched or poorly crimped plug pairs are a common source of heating and arcing.
Key takeaways
- Size cables for both ampacity and voltage drop.
- Apply temperature, grouping and installation derating.
- Never mix unverified connector brands or types.
- Use correct crimp tools, torque and weatherproof routing.
Current-carrying capacity
Determine design current from the PV string or circuit configuration and apply the required factors. Then use manufacturer current-rating tables for the installation method, ambient temperature, grouping and enclosure conditions. Cable ampacity cannot be selected from a generic amps-per-square-millimetre rule alone.
- Start from module Isc and string arrangement.
- Apply continuous-current and correction factors.
- Check conductor temperature rating.
- Coordinate with fuse and breaker protection.
Voltage-drop calculation
DC cable voltage drop depends on circuit current, loop length, conductor resistance and cross-sectional area. Long rooftop or ground-mounted routes may require a larger size than ampacity alone. Lower loss can improve lifetime energy, but excessively large cable may be difficult to terminate and uneconomic.
- Use the complete positive-and-negative circuit length.
- Evaluate loss at realistic operating current.
- Confirm connector and terminal size limits.
- Balance capital cost with energy loss.
Connector compatibility and crimping
Similar-looking solar connectors are not automatically compatible. Mixing connector families can create poor contact pressure, seal failure or warranty problems. Use matched components from an approved system and the specified crimp tool. Inspect conductor insertion, crimp geometry, gland sealing and final engagement.
- Do not mate unverified cross-brand connectors.
- Use the correct conductor size and preparation.
- Perform pull and visual checks.
- Keep connectors off the roof surface and away from water traps.
Routing and protection
Support cables to prevent movement, abrasion and standing water. Maintain bend radius, segregation and protection at sharp edges or exposed locations. Route positive and negative conductors together where appropriate to reduce loop area, and coordinate cable paths with lightning and fire-safety design.
- Use UV-resistant supports suitable for the environment.
- Avoid loose cable loops beneath modules.
- Protect entries and penetrations.
- Label circuits at accessible isolation points.
Frequently asked questions
Is 4 mm² solar cable enough?
It may be suitable for some strings, but final size depends on current, length, voltage drop, temperature, grouping and installation method.
Can ordinary building wire be used outdoors for PV DC?
Use cable designed and certified for the required PV voltage, temperature and environmental exposure.
Can different MC4-style brands be connected?
Do not assume compatibility. Use matched, approved connector pairs and manufacturer instructions.
Turn guidance into a practical system plan
Use Spectra’s engineering calculators for a preliminary estimate, then request technical verification before purchase or installation.