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NOTE: The PV breakers in the IQ Combiner 6C cannot be oversized and must be sized to the PV <br />nameplate rating. <br />NOTE: For this MPU avoidance use case to be accepted by an AHJ, the AHJ must recognize <br />PCS. PCS is part of the 2020 edition of the NEC. The edition of NEC in effect in various states <br />can be found on the NFPA website. <br />5.3.4 Failure mode and resolution for MPU avoidance <br />Enphase Power Control is designed for robustness. The system ensures adherence to the NEC <br />guidelines of current back-fed even when one or more devices have stopped communicating with <br />the IQ Gateway. <br />Table 5: Failure mode and solution mechanism <br />Failure mode Resolution mechanism <br />Production, Battery, Backfeed, or <br />Consumption CTs not reporting the <br />correct value or missing <br />PV production current and IQ Battery current will be curtailed to a safe <br />limit. <br />IQ Battery communication failure If the IQ Gateway loses communication with the IQ Battery for more <br />than 20 seconds, the IQ Battery discharge is completely curtailed. <br />Microinverter communication failure If IQ Gateway loses communication with the microinverter for more <br />than 10 seconds, PV production will be curtailed to the safe limit. <br />PCS controller or IQ Gateway failure <br />If the IQ Gateway loses communication with the microinverters for more <br />than 10 seconds and with the IQ Battery for more than 20 seconds, all <br />PV and IQ Battery discharges are curtailed to a safe limit. <br />5.3.5 Configuring MPU avoidance through the Enphase Installer App <br />Under System Details, go to Site Configuration > PCS Based Limiting > Main Panel Upgrade <br />Avoidance, as shown in the following figure. <br />Enphase Power Control features <br />33 © 2025 Enphase Energy Inc. All rights reserved. August 2025 <br />TEB-00269-2.0-EN <br />NOTE: For MPU avoidance with Busbar Overload Control, Consumption CTs or Meter Collar <br />must be placed between the main panel and the utility meter. <br />In the PCS Export Limiting > Main Panel Upgrade Avoidance section, the installer has three ways of <br />setting up the feature: <br />•Busbar Overload Control: In this option, the installer adds information on the rating of the main <br />load panel, the main service breaker, and the main DER breaker. The system utilizes these inputs to <br />configure the Busbar Overload Current feature, complaint with 2020 NEC 705.13 (A) through (E). <br />•Current Limit with NEC 120% rule: In this option, the installer adds information on the rating of the <br />main load panel busbar and the main service breaker rating. The system then auto-calculates the <br />export current limit based on the 2020 NEC 705.12 (B) (2) or (4) rule. <br />•Current Limit Directly Entered: There may be situations where a homeowner may have an <br />additional DER system connected to the main panel that is not monitored by the Enphase <br />Power Control feature. This could be a DER from another manufacturer or Enphase’s legacy <br />microinverters. In either case, the installer needs to account for the current being back- <br />fed from such a system and ensure they limit the maximum current export value of the <br />Enphase Energy System so that the total current exported back to the grid remains compliant <br />with the NEC guidelines. <br />The following figure shows the MPU avoidance configuration with Busbar Overload Control. <br />Enphase Power Control features <br />34 © 2025 Enphase Energy Inc. All rights reserved. August 2025 <br />TEB-00269-2.0-EN