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Generac•SnapRS

Analysis by Marcus & Team

Generac SnapRS: MC4 Connector Charring

Troubleshoot charring on MC4 connectors of a Generac SnapRS rapid shutdown device in a residential solar system. Diagnose, repair, and ensure NEC compliance.

Frequently Asked Questions

•What is the proper torque specification for MC4 connectors on Generac SnapRS units?

Refer to the Generac SnapRS installation manual for the correct torque specification, typically 2-3 Nm.

•How can I safely verify that the rapid shutdown system is functioning correctly?

Use a calibrated multimeter to measure the voltage at the array boundary after initiating rapid shutdown. The voltage should be less than 30V within 30 seconds.

•What type of MC4 connectors are compatible with Generac SnapRS units?

Use UL listed MC4 connectors that are specifically rated for the voltage and current requirements of the Generac SnapRS system and PV modules.

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Marcus leads the technical research department at Storage Faults. Together with a team of systems analysts, he specializes in translating complex solar storage error codes into actionable diagnostic steps for the US market.

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Technical Background:

The Generac SnapRS is a module-level rapid shutdown device (RSD) designed to comply with NEC 2017/2020 rapid shutdown requirements. It reduces voltage to safe levels (<30V) within 30 seconds of initiation. The SnapRS connects in series with the PV module output and communicates with the inverter to enable or disable power flow. Charring on MC4 connectors indicates increased resistance, leading to heat generation (I²R losses). This can be caused by poor crimps, loose connections, corrosion, or excessive current.

Step-by-Step Fix:

1

*Safety First:** Initiate the rapid shutdown procedure following Generac's guidelines and NEC 690.
2

Verify voltage at the array boundary is <30V using a calibrated multimeter.
3

*Visual inspection:** Carefully inspect all MC4 connectors on the affected string, documenting the severity of charring and any signs of water ingress.
4

*Disconnect & Test:** Wearing appropriate PPE (Personal Protective Equipment), disconnect the affected SnapRS unit. Use a calibrated multimeter to measure the open-circuit voltage (Voc) and short-circuit current (Isc) of the PV module. Compare these values to the module's datasheet.
5

*Connector inspection:** Disassemble the MC4 connectors (using an MC4 disassembly tool) and inspect the crimp connections for corrosion or damage. Verify the crimp is secure and meets the manufacturer's specifications.
6

*Resistance Measurement:** Using a low-resistance ohmmeter, measure the resistance across the MC4 connector. A high resistance indicates a faulty connection.
7

*Replacement:** Replace any damaged or corroded MC4 connectors with new, properly crimped connectors that are UL listed and compatible with the Generac SnapRS system. Ensure correct polarity.
8

*Torque Verification:** Reassemble the MC4 connectors, applying the correct torque as specified by the manufacturer (typically 2-3 Nm). Document all findings and actions taken.

Common Causes:

Insufficient crimp on MC4 connector leading to high resistance.
Loose MC4 connector causing arcing and oxidation.
Water ingress or corrosion within the MC4 connector.
Exceeding the maximum current rating of the MC4 connector or SnapRS unit.
Manufacturing defect in the MC4 connector or SnapRS unit.
Improper torque applied during system.

Observed Symptoms:

Visible charring observed on the MC4 connectors of a Generac SnapRS unit installed in a residential solar array. This indicates a potential issue with electrical conductivity and overheating.

Preventative Care:

Regularly inspect MC4 connectors for signs of corrosion or damage (at least annually).
Use a thermal camera or IR thermometer to scan connections for hotspots during peak sunlight hours.
Ensure proper torque is applied to all MC4 connectors during system.
Periodically re-torque connections to prevent loosening due to thermal cycling.
Use dielectric grease inside the MC4 connector during system to prevent corrosion.