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current being back-fed to the main panel increases beyond 32 A, the IQ Gateway sends a signal to PV <br />microinverters and the battery to limit their production and discharge, respectively. <br />NOTE: The PV branch breakers in the IQ Combiner cannot be oversubscribed and must be sized <br />to the nameplate of the PV on the respective branches. <br />MPU avoidance in grid-tied configuration supports a maximum PV nameplate rated output of 80 A <br />and a maximum battery nameplate output (to limit per-phase backfeed levels to the main panel) of <br />118 A. <br />In systems with IQ Battery 10C, MPU avoidance in grid-tied configuration works in conjunction with <br />IQ Battery over-subscription. <br />Operation with IQ Battery over-subscription <br />For example, in the preceding figure, the Ibackfeed allowed is 32 A. If Iproduction is 0 A, the maximum <br />allowed Ibattery is 32 A. However, consider a scenario where IQ Battery over-subscription is enabled <br />with the Battery breaker on IQ Combiner as 20 A. Ibackfeed allowed remains 32 A, but if Iproduction is 0 A, <br />the maximum allowed Ibattery is 16 A. <br />In grid-forming configuration <br />MPU avoidance in grid-forming configuration, when the option for NEC 120% rule or the current <br />limit directly entered is selected, the feature continuously monitors the current being produced <br />cumulatively by the installed PV array and the IQ Battery using integrated backfeed CTs. It then limits <br />the produced power in real time based on the current limit imposed by the NEC 120% rule. <br />The following figure shows this grid-forming configuration feature. <br />Enphase Power Control features <br />31 © 2025 Enphase Energy Inc. All rights reserved. August 2025 <br />TEB-00269-2.0-EN <br />IQ EV Charger <br />Ibackfeed <br />* I p r o d u c <br />Integrated Production CT <br />Integrated Backfeed CTs <br />N13 <br />RS+GNDRS- <br />NO <br />NC <br />C <br />EIP comm. LED <br />USB1 <br />USB2 RSD LED <br />Status LED <br />Reset <br /> button <br />AP mode LED <br />AP mode button <br />Power production LED <br />Device comm. LED <br />Device scan button <br />Backfeed lugs <br />with DER relay <br />PV bus DER bus <br />DER centre <br />IQ PV2 <br />IQ PV3 <br />IQ PV1 <br />11 <br />_ <br />N <br />3 4 <br />12 <br />A1 <br />5 6 7 8 <br />910 <br />A2 <br />Combiner Controller Board (CCB) <br />Gateway <br />1 2 3 4 D 1 2 3 4 D <br />CT8(L2)IQ PV4 <br />IQ B2 <br />IQ B1 <br />IQ EVC <br />PVA <br />PF <br />CT2, CT3 <br />CT1 <br />CT4, CT5 <br />CT(L1)CT(L1)CT(L2)CT (L2) <br />IQ Combiner 6C <br />Load Controller <br /> <br />B1 <br />LCB <br />CT6, CT7 <br />1 <br />1 2 3 4 D <br />2 <br />1 2 3 4 D <br />N <br />Grid <br />Backed up <br />home loads <br />Non-backup <br />heavy loads <br />IQ BatteryIQ Series Microinverters IQ Battery <br />Connect to EVSE <br />CT connector on <br />the gateway <br />Integrated Battery CTs <br />Integrated <br />Consumption CTs <br />Main Panel Upgrade Avoidance <br />with Feeder Control <br />Main DER <br />breaker <br />11 <br />Main-meter combo <br />with IQ Meter Collar <br />behind the utility meter <br />(back-fed panel) <br />Figure 9: MPU avoidance with Feeder Control in grid-forming configuration <br />System sizing with MPU avoidance using the NEC 120% rule or the current limit directly entered in a <br />grid-forming system <br />For example, as seen in the preceding figure, if the main load panel busbar is 200 A and the grid size <br />breaker is also 200 A, the maximum continuous current backfeed allowable from the IQ Combiner 6C <br />to the main panel is limited to ((120% × busbar rating) – main breaker size)/125% = total DER current <br />((120% × 200) – 200)/125% = 32 A. <br />Therefore, in this scenario, the system ensures that no more than 32 A of continuous current is <br />back-fed to the main panel. <br />Enphase Power Control features <br />32 © 2025 Enphase Energy Inc. All rights reserved. August 2025 <br />TEB-00269-2.0-EN