This guide focuses on MC4 connectors, but the same concepts apply to other interlocking PV connectors like Amphenol H4, Tyco, and SMK.

How to Use MC4 Connectors and MC4 Extension Cables

MC4 connectors, available in male and female types, are locking connectors commonly used in modern solar modules. MC4 extension cables come in various lengths, such as 8 ft, 15 ft, 30 ft, 50 ft, and 100 ft. These connectors simplify solar panel wiring by replacing the older method of manually attaching wires to terminal posts on the panel’s junction box. While this older approach is still seen in smaller panels, MC4 connectors dominate due to their efficiency and ease of use.

These connectors snap securely together, are UL-certified, meet National Electric Code standards, and are preferred by inspectors. Their locking mechanism ensures they remain connected in outdoor environments. Disconnecting them requires a specialized MC4 unlocking tool.

Each MC4 connector consists of two parts: the contact and the plastic housing. The contact determines whether the connector is male or female—not the housing.

Series vs. Parallel Connections

  • Series Connection (Strings): In a series setup, the positive lead of one panel connects to the negative lead of another. This increases the total voltage while keeping the current constant. For example, two panels rated at 18 volts (Vmp) will produce 36 volts when connected in series.
  • Parallel Connection (Branches): In parallel wiring, positive leads are connected together, and negative leads are joined as well. This increases the current while maintaining constant voltage. For example, two panels rated at 8 amps (Imp) will produce a total of 16 amps when wired in parallel.
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Wiring Modules with MC4 Connectors

Series Wiring

To wire panels in series:

  1. Identify the DC positive (+) and negative (-) leads on each module.
  2. Typically, the positive lead has a female connector, while the negative lead has a male connector. Verify polarity using markings or a digital voltmeter.
  3. Connect the positive lead of one panel to the negative lead of another using their respective connectors.

This setup increases voltage while keeping current constant. For instance, three panels rated at 18 volts (Vmp) each will produce a total of 54 volts when connected in series.

Parallel Wiring

For parallel connections:

  1. Join all positive leads together and all negative leads together.
  2. Use MC4 multibranch connectors for small setups (e.g., two panels). These connectors combine multiple leads into one output.
  3. For larger setups involving more than two panels or strings, use a PV combiner box instead of multibranch connectors.

Parallel wiring increases current while maintaining voltage. Ensure appropriate wire sizing to handle increased current and prevent voltage drops.

Using MC4 Extension Cables

MC4 extension cables function like electrical extension cords, with male and female connectors on opposite ends. They connect solar panels to electrical equipment like charge controllers or combiner boxes.

When selecting cable length:

  • Measure the distance between your solar array and equipment.
  • If using a single cable for longer distances, cut it into two sections—one with a male connector and another with a female connector—to match your panel leads.
  • For long distances (e.g., house installations), use extension cables to connect panels to a combiner box and then switch to less expensive wiring inside conduits for cost efficiency.
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Disconnecting MC4 Connectors

To disconnect an MC4 connection:

  • Use an MC4 disconnect tool.
  • Insert its posts into the female connector’s side to release the locking mechanism.
  • Separate the male and female connectors. 

Building MC4 Cables

Creating custom MC4 cables requires:

  • A crimping tool to attach contacts to wires.
  • Placing a lock ring on the wire before securing it inside the housing.
  • Tightening the lock ring using an MC4 disconnect tool as a wrench.

Key Specifications of MC4 Connectors

  • Manufacturer: Multi-Contact USA
  • Maximum current: 30 amps (connector rating)
  • Maximum voltage: 1,000 volts
  • Temperature range: -40°C to +90°C (-40°F to 194°F)

Important: Do not remove factory-installed MC4 connectors from solar modules; doing so may void your warranty.