Enphase › current transformers and metering
Production CT reads negative during commissioning
reported more than once
Symptoms
- During CT commissioning the production reading or its L1 value is negative, consumption L1 or L2 is negative, production does not fall to 0 W with the PV breakers off, consumption shows overnight with no load, metered consumption exactly mirrors production, or a site with two PV systems reports negative daytime consumption
- Enphase's own storage-commissioning webinar puts CT installation errors at up to 50% of sites. Found later, in service, the same errors show as a battery whose discharge power swings wildly over seconds with steady household load, causing needless grid imports and exports (one reported case: consumption CT reading backward and battery CT polarity flipped), or a newly added battery system that exports to the grid instead of charging because an older, separate solar system's output is being read into its measurements. Two reported cases with the same runtime symptoms had other install causes: batteries mounted a long AC run (130 ft of AWG 8) from the load centre over-reacted to demand feedback through voltage rise on the run, and a system that stopped discharging fully overnight turned out to have a changed reserve setting, a tripped combiner breaker and a weak Zigbee link. A CT placement that is by design rather than by mistake gives a related picture: on a partial-home backup designed under Enphase's older feeder-control power control system (the 120% busbar rule), the consumption CTs sit on the feeder between the storage system and the main panel, so consumption reads far too low, the battery never discharges to cover the main-panel loads, and the microinverters curtail themselves to the back-feed limit even when the home could use the power
The cause and the fix
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