Ampacity Calculations For Iq8D Microinverter System; Branch Circuit Current Calculations; Figure 65: Qd Cable Rotation For Iq8D Ac Branch Circuit - enphase IQ8D-72-E-US Design Manual

Ampacity Calculations for IQ8D Microinverter
System
Enphase IQ8D Microinverter supports two series connected PV modules and has a four pin output configuration (L1, L2,
L3 and Neutral Sense) with Power on two pins and phase sensing on the other two pins.
IQ8D Microinverters are connected across the L-L 208V connection. The Single-Phase IQ8D Microinverter achieves the
three-phase configuration and phase balancing using the three phase QD Cable rotation. Figure 65 shows phase rotation
of QD Cable for a branch circuit of 9 IQ8D Microinverters. As shown, the QD Cable rotation creates a balanced 3 phase
configuration with L1-L2: 3 Microinverters; L2-L3: 3 Microinverters and L1-L3: 3 Microinverters connected across each
phase.
The branch circuit calculations shall involve vector mathematics for current addition as each Microinverter is connected
across L-L shall contribute current to all 3 lines – L1, L2 and L3 conductors. To simplify the current calculations please
refer to the following formulas. We shall use √3 multiplier for converting phase current to line current.

Branch Circuit Current Calculations

The equation to calculate ampacity for one branch in a 208V three-phase system is:
Current (amps per branch) = [(Maximum continuous output power of Microinverter) × (maximum number of Microinverters
per phase L-L) ×√3] ÷ (208 volts)
The equation to determine OCPD sizing for a three-phase system is:
OCPD Sizing = [(Maximum continuous output power of Microinverter) × (maximum number of Microinverters per phase
L-L) × √3 ] ÷ (208 volts) × 1.25 (Safety Factor)
Use these calculations to determine ampacity in three-phase systems as shown in the following sections.
NOTE: Each of the three-line conductors in a balanced three-phase system carries this current. The neutral sense does not carry any current
but is used for Microinverter communications and sensing.
NOTE: In case of an imbalanced system where each phase has different number of Microinverters, consider the largest number of
Microinverters in a phase for OCPD sizing calculations.
© 2022 Enphase Energy Inc. All rights reserved.

Figure 65: QD Cable Rotation for IQ8D AC Branch Circuit

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