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NOTE: For MPU avoidance with Busbar Overload Control and IQ Combiner 6C, the maximum main DER breaker size (backfeed breaker size) is limited to 125 A. For example, as seen in the preceding figures, if the main load panel busbar size is 100 A and the grid-side main service breaker size is also 100 A, the maximum continuous current backfeed allowable from the IQ Combiner to the main panel is limited to 80 A (the minimum of three values: 100 A, 80% of 100 A, or 125 A). Therefore, in this scenario, the main DER breaker can be sized up to 80 A. The system ensures that the production and battery current is limited such that the current in the busbar never exceeds 100 A by monitoring the Production CT, Battery CT, and Consumption CTs. 5.3.3 MPU Avoidance with Feeder control (using NEC 120% or current limit directly entered) In grid-tied configuration When selecting the option to use MPU avoidance using the NEC 120% rule or current limit directly entered in grid-tied configuration, the feature continuously monitors the current being produced cumulatively by the installed PV array and the IQ Battery using integrated backfeed CTs. It then limits the produced power in real time based on the current limit imposed by the NEC 120% rule. The following figure shows this grid-tied configuration feature. Enphase Power Control features 29 © 2025 Enphase Energy Inc. All rights reserved. August 2025 TEB-00269-2.0-EN Main panel (Back-fed panel) IQ Series Microinverters IQ EV Charger Connect to LC CTs/Cons CTs Connector N N13 RS+GNDRS- NO NC C EIP comm. LED USB1 USB2 RSD LED Status LED Reset button Main DER breaker AP mode LED AP mode button Power production LED Device comm. LED Device scan button Backfeed lugs with DER relay PV bus DER bus DER centre IQ PV2 IQ PV3 IQ PV1 11 _ N 3 4 12 A1 5 6 7 8 910 A2 Combiner controller Board Integrated Production CT Ibattery Integrated Battery CTs Gateway 1 2 3 4 D 1 2 3 4 D CT8(L2) IQ PV4 IQ B2 IQ B1 IQ EVC PVA PF CT2, CT3 CT1 CT4, CT5 CT(L1)CT(L1)CT(L2)CT (L2) IQ Combiner 6C Home loads Connect to EVSE CT connector on the gateway 11 Utility meter Grid IQ Battery IQ Battery Load Controller B1 LCB CT6, CT7 1 1 2 3 4 D 2 1 2 3 4 D CT9, CT10 (L1,L2) Integrated Backfeed CTs Ibackfeed Main Panel Upgrade Avoidance with Feeder Control Additional loads 8 Figure 8: MPU avoidance with Feeder Control in grid-tied configuration The battery discharge is controlled first, followed by the PV production current to limit Ibackfeed entering the main DER breaker in the main panel. The main DER breaker must be sized to the PCS limit as per NEC 2020 705.13 (C). System sizing for MPU avoidance with the NEC 120% rule and the current limit directly entered in a grid-tied system For example, as seen in the preceding figure, if the main load panel busbar size is 200 A and the grid-side main service breaker size is also 200 A, the maximum continuous current backfeed allowable from the IQ Combiner to the main panel, Ibackfeed, is limited to: ((120% * busbar rating) – main service breaker size)/125% = total DER current ((120% * 200)-200)/125% = 32 A. In this scenario, the system ensures that no more than 32 A of continuous current is exported back to the main panel. The integrated backfeed CTs inside the IQ Combiner 6C will monitor the current being back-fed into the main panel in real time and feed this information to the IQ Gateway. If the Enphase Power Control features 30 © 2025 Enphase Energy Inc. All rights reserved. August 2025 TEB-00269-2.0-EN