Design Considerations For Voltage Rise; Recommendations - enphase IQ8 Design Manual

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Ensure cables enter the junction box from the side or from the bottom, never from the top,
where water can enter the enclosure.
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Install cables with a drip loop. Secure the cable so that water drains away from the cable
entry.
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Use properly sized strain reliefs and cord grips. Note that the QD Cable is circular with an
outer diameter of 11.5 mm (0.45 inches). The cable gland securing the QD Cable must contain
an inner gland sized for the QD Cable.
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Properly tighten the strain reliefs to prevent cable movement and to prevent water ingress.
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Install the junction box to meet the manufacturer's mounting and orientation requirements.
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Use NEMA 4 enclosures. (NEMA 3 enclosures have a limited mounting orientation range and
may not accommodate typical rooftop installations.)
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Consider drilling a small drain hole in the bottom, lowermost corners of the junction box so
that moisture or condensate can drain out of the junction box.

2.3 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 IQ8 Commercial 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 loss, less heat at the terminals, and improved
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, the voltage rises
at the AC terminals of each inverter. Therefore, this brief refers to these calculations as voltage rise
(VRise).

2.3.1 Recommendations

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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 circuit breakers; however, if you design for a 2% total voltage rise, these other factors
may be ignored. A 2% VRise limit in the IQ8 Commercial Microinverter system design shall
ensure high-quality installations with lower energy losses and higher system reliability.
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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 the total VRise for the entire
system for the farthest microinverter in the branch circuits from the point of common
coupling.
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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 or junction box to the farthest
microinverter by center feeding and creating sub-branch circuits 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)
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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.
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When installing the IQ8 Commercial Microinverter system using QD Cable, you may have
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IQ8 Commercial Microinverter grid-tied PV system
November 2023
USG-00026-1.0