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Fox ESS Res Cur Fault

Updated June 2026 · Reviewed for technical accuracy · ~2 min read
⚠️ This is a real safety fault, not a glitch. Res Cur Fault means current is leaking to earth inside your PV system. Do not keep resetting the inverter to make it go away. Repeated current leaking to earth is a genuine shock hazard, so the array needs a qualified installer to find and fix the leak before the inverter is restarted.

Res Cur Fault (residual current fault) means the inverter's internal RCD has measured excess residual current, the difference between the current flowing out and coming back, which indicates real current leaking to earth. It usually points to defective insulation or a ground fault somewhere in the PV array or the DC cabling. The Res Cur HW Fault variant means the RCD monitoring board itself has failed and the inverter can no longer trust its own leakage measurement. Either way, the inverter stops generating on purpose to keep you safe.

What usually causes it

  • Water ingress. Moisture in a junction box, an MC4 connector, or the DC cabling is the most common cause, often after rain or in a damp roof space.
  • Damaged or degraded insulation. A cable rubbing on a sharp edge, rodent damage, or old, perished insulation lets current escape to earth.
  • A ground fault in the array. A panel or string developing a short to its frame or to the mounting structure.
  • A failed RCD monitoring board (the HW variant). The internal residual-current hardware has failed and the reading can no longer be trusted, which is an inverter-side fault.

How to handle it safely

  1. Do not keep resetting it. A single power-cycle to clear a one-off trip after heavy rain is reasonable. If it returns, stop. Repeated resets do not fix a leak, they just remove the protection.
  2. Look (do not touch) for obvious water. From the outside, check whether junction boxes or connectors look full of water or visibly damaged. Never open a live DC connector or cut into cabling yourself.
  3. Note the pattern. Does it trip only when it rains, in the morning dew, or all the time? This timing helps your installer pinpoint the leak quickly.
  4. Call your installer. A residual current fault needs proper insulation-resistance testing of the strings to locate the leak. This is a diagnosis-and-repair job, not an owner reset.
  5. Confirm the protective device. Fox ESS specifies a bi-directional 100mA RCD/RCBO on the external AC side. Have your installer verify the correct device is fitted while they are on site.
When to call a professional. Call your installer now and leave the inverter off until they arrive if Res Cur Fault keeps coming back, if you see water or damage in any junction box or connector, or if you ever see the Res Cur HW Fault variant. Do not open live DC connectors, do not bypass the protection, and do not keep restarting to force generation. A persistent earth-leakage fault is a shock risk that only a qualified person should clear.

Related Fox ESS codes

ISO Fault DCI Fault Arc Fault

FAQ

Res Cur Fault only appears when it rains, can I just ignore it?

No. A trip that tracks the weather is a strong sign of water getting into a connector or junction box and leaking current to earth. It may clear when things dry out, but the underlying path is still there and will get worse. Have an installer find and seal the entry point rather than waiting for the next wet day.

What is the difference between Res Cur Fault and Res Cur HW Fault?

Res Cur Fault means the inverter genuinely measured too much current leaking to earth in your array or cabling. Res Cur HW Fault means the inverter's own residual-current monitoring board has failed, so it can no longer trust that measurement. Both stop generation for safety, and both need an installer. The HW variant is an inverter hardware fault rather than a wiring problem.

Helpful guides

Error codes explained How to safely restart your inverter What is an arc fault

Sources

  • Fox ESS H1/AC1 inverter user manual and FoxCloud alarm list (Res Cur = residual current above limit; check PV insulation and the external protective device).
  • Fox ESS installer guidance on residual-current monitoring and the required bi-directional 100mA RCD/RCBO.
⚠️ Safety disclaimer. Solar inverters carry lethal DC and AC voltage even when "off". A residual current fault means current is leaking to earth, which is a shock hazard. Visual inspection from the outside is the limit of owner checks. All testing, connector work, and internal repair must be done by a licensed installer or electrician.