We occasionally receive questions from installers who notice that the maximum input current shown on a datasheet appears higher than the breaker and cable sizing recommended in the installation manual. A typical example is the H1-G2 3.7, which lists a theoretical AC input current of 34.9 A, while the manual recommends a 25 A breaker when the EPS function isn’t used. At first glance, this can look like an undersized protective device – but it isn’t. The difference simply reflects the two different operating modes of all Fox ESS single-phase hybrid inverters.
Why the Datasheet Shows a Higher “Maximum Input Current”
The higher current figure (e.g., 34.9 A) represents the theoretical maximum AC input current only when the EPS function is active. When EPS is enabled, the inverter can:
- Charge the battery from the grid, and
- Supply power to EPS-backed circuits at the same time.
Because the EPS output operates as a bypass path, the combined flow of charge current and EPS load current can raise the total AC input current above what is ever seen in standard operation. This is why the datasheet must reflect the absolute upper limit that could technically be reached in this combined-mode scenario.
Why the Manual Recommends Smaller Breakers When EPS Is Not Used
In the vast majority of installations, EPS is not utilised.
In this standard operating mode:
- The inverter behaves purely as a grid-connected hybrid inverter/charger
- The AC current draw relates only to charging and export/import behaviour, not EPS load support
- The rated output current on a model like the H1-G2 3.7 is well within what a 25 A breaker is designed for
- The system will never approach the 34.9 A figure, because the EPS bypass pathway is inactive
Therefore, the breaker and cable sizing guidance in the installation manual is correct and appropriately rated for non-EPS installations. It is not undersized—it’s simply based on the operating conditions that apply in normal mode.
In Simple Terms
- Datasheet value (e.g., 34.9 A)
→ Only relevant if EPS is active, because the inverter can support EPS loads and charge the battery simultaneously. - Manual recommendations (e.g., 25 A breaker)
→ Correct for standard installations where EPS is not used. - Rated output current
→ Dictates breaker and cable sizing in standard grid-connected operation, not the theoretical EPS-combined value.
Always Refer to the Product Manual
For all Fox ESS single-phase hybrid inverters, the installation manual is the definitive source for cable sizing, breaker requirements and wiring guidance.
The datasheet lists the absolute technical limits, but the manual provides the correct values based on the actual installation mode and expected current behaviour.
