Design Considerations For Voltage Rise; Recommendations - enphase IQ8D-72-E-US Design Manual

Design Considerations for Voltage Rise

This section describes the Voltage rise guidelines for
dedicated PV branch circuits and methods for calculating
the AC line voltage rise when using the Enphase IQ8D
Microinverters and the Enphase QD Cable.
Applying proper voltage rise calculations during your
system design helps prevent nuisance voltage out-of-range
trip issues due to high line voltage conditions.
Less resistance in conductors also results in less power

Recommendations

• Although the National Electric Code recommends that
branch circuit conductors be sized for a maximum
of 3% VRise (Article 210.19, FPN 4.), this value in
practice is generally not low enough for a utility
interactive inverter. Additional losses exist at the
terminals, connectors, and in circuit breakers; however,
if you design for a 2% total voltage rise, these other
factors may be ignored. A 2% VRise limit in the IQ8D
Microinverter system design shall ensure high quality
installations with lower energy losses and higher
system reliability.
• Enphase recommends that the total percentage of
voltage rise in the AC wiring be a maximum of 2%,
which includes a less than 1% voltage rise in the QD
Cable. Although the QD Cable is optimized for minimal
VRise, it is still important to calculate total VRise for
the entire system for the farthest Microinverter in the
branch circuits from point of common coupling.
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loss, less heat at the terminals, and improves performance
of the PV system.
When designing circuits for electrical loads, these
calculations are commonly called voltage drop (VDrop).
Since PV systems with inverters generate electricity
instead of consuming it, voltage rises at the AC terminals
of each inverter. Therefore, this brief refers to these
calculations as voltage rise (VRise).
• It is recommended to Center-feed the branch circuit
to minimize voltage rise in a fully populated branch
circuit. Since the VRise is nonlinear, reducing the
number of Microinverters on a QD Cable from the field
wireables/junction box to the farthest Microinverter
by center feeding and creating sub-branch circuits
greatly reduces the voltage measured at the farthest
Microinverter in each sub-branch. To center-feed a
branch, divide the circuit into two sub-branch circuits
protected by a single overcurrent protection device
(OCPD)
• Use the correct wire size for the AC extension cables
and home-run cables during the system design. Using
undersized conductors can result in nuisance tripping
of the Microinverter when an AC voltage out-of-range
condition occurs.
• Refer : "Technical Brief on Calculating AC line voltage
rise for IQ8D Microinverter with QD Cable" for VRise
calculation method details at enphase.com/support.
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