MC4 Connectors Explained: Sizes, Crimping & Compatibility
Learn what MC4 means, how to match connectors to cable size and how to crimp them step by step. We also cover genuine versus compatible parts, because mixing brands is risky.
What an MC4 connector is
MC4 is the standard DC connector for solar. It is a weatherproof, locking male and female pair rated to IP67 or better. It carries panel-level DC current safely outdoors for decades.
Nearly every modern panel ships with MC4-style leads. For that reason the connectors, and the tools to fit them, are must-have parts of any system. They sit alongside the cable, the fuses and the mounting in what installers call the balance of system.
Matching connectors to cable size
MC4 connectors are sized to the cross-section of the cable. UK solar cable is usually 2.5mm², 4mm² or 6mm². Each size needs the correct crimp barrel inside the connector, because that keeps the joint secure and low in resistance.
The wrong barrel is a common cause of hot joints and failures. Therefore, order the connector to match your cable, not the other way round. If you are unsure of the size, check the print on the cable sheath before you buy.
Genuine versus compatible
The original MC4 is made by Stäubli. Many connectors on the market are sold as MC4-compatible. Both can be perfectly good, although one safety rule matters most. Never mate two different brands in the same joint.
Mixed brands can look fine and still make poor mechanical and electrical contact. That is exactly where connector fires start, so keep each connection to one brand from end to end.
How to crimp an MC4 (step by step)
- Strip the solar cable to the length set for the connector. Do not nick any strands.
- Slide the housing and seal onto the cable before you crimp the metal pin.
- Put the conductor into the correct crimp barrel and crimp it with a ratchet MC4 tool.
- Push the pin into the housing until it clicks home, then hand-tighten the gland.
- Test-mate the pair. It should lock with a positive click and not pull apart.
Safety and compliance
Solar DC can be live whenever there is daylight. Never make or break MC4 connections under load, so isolate at the DC isolator first. Use a proper ratchet crimp tool rather than pliers, and keep connectors to one brand throughout a joint.
Fit in-line DC fuses and isolators where the system design calls for them. Since the joint is part of the live circuit, a proper job matters. Done properly, an MC4 joint is as reliable as the cable itself.
Where to buy and what to read next
Browse MC4 connectors, solar cable and crimping tools in our cabling and connectors category. Matched sets take the guesswork out. For example, the panels in a solar panels and kits order usually arrive with leads fitted, but you still need spare connectors for longer runs.
The cable also has to suit the rest of the system. Our solar panel kits buying guide shows how to measure your cable runs, and the solar inverter comparison covers the input limits of each inverter type. If you plan to add storage, our guide to home battery storage cost sets out the likely prices.
You can also see the inverters and mounting and fixings ranges to finish the job. Installers who buy connectors in bulk can ask about trade and bulk pricing.
Where to go next
Connectors are only one part of the wiring, so see our full range of cabling and connectors. Because every array needs panels, an inverter and fixings, also browse solar panels and kits, solar inverters and mounting and fixings.
To plan the whole system, read the kit buying guide, the inverter comparison and the home battery cost guide. Buying in volume? Ask about trade and bulk pricing, or look at battery storage.