by Rebekah Hren – SEIPS Senior Technician and PV System Designer – Solar Energy International Principal, CMP-4 of the National Electrical Code

Whether drafting an equipment layout for an engineered planset, physically mounting equipment, or inspecting and commissioning a solar PV system, it’s important to keep clearances in mind. Of course the first place to start is with National Electrical Code required workspace clearances, found in NEC Section 110.26 and Table 110.26(A)(1). The requirements in these sections were expanded in the last NEC code cycle to apply up to 1000V, whereas in the 2014 NEC requirements for over 600 volts were in a separate Section, 110.30 and Table 110.34 (which is now where requirements for 1500Vdc systems can be found).

But equally important—or perhaps even more important—is reading the installation manual for equipment. Frequently, the clearances required in the manual, particularly for string inverters, will exceed the NEC requirements. Disregarding installation manuals will likely void the warranty. Don’t forget that NEC Section 110.3(B) requires following the installation instructions included with listed products.

For example, minimum NEC workspace clearances would allow 1000Vdc inverters to be mounted on a wall with no space between them (provided the enclosure door opens 90 degrees), and there is sufficient width (30”) to stand in front in the equipment, sufficient headroom (6-1/2’), and sufficient depth of working space (between 3’ and 5’ depending on the Condition). However, if you dive into most inverter manuals, you’ll find clearances required around inverters of anywhere from 4” to 18”—or even more—for airflow and cooling purposes. Another installation requirement that will only be found in the manual is allowances for mounting the equipment in a non-vertical position, whether flat on a roof or at a tilt angle. Sometimes you can, sometimes you can’t: it depends on the NEMA rating and specifics of the equipment.

What if you have a standing rack and want to mount inverters back to back? Again, read the manual! You should find a diagram that lays out minimum clearance on all sides of the equipment, including minimum height above grade. Regardless of the manufacturer-required height above grade, remember to take the conditions of the site into account, and keep inverters out of direct sunlight, snow drifts, and out of the way of grounds maintenance equipment.

While you are at it, don’t forget to take a look at the maximum conduit and maximum conductor allowances for equipment—planning ahead of time for the right size conduit and conductors will save a lot of trouble and extra parts on site. With long conductor runs, voltage drop can push up conductor and conduit sizes above what equipment is designed for, which means a transition may be required to bring conduit and conductors into spec.

For SEIPS site inspections, I bring a tape measure to every job site and make sure I have a copy of the most recent equipment manuals. Throughout the installation, it is important that installers have easy access to check these manuals. It’s easy for clearances to get lost in the details, but it is critical for proper PV system operation, service, and longevity.

Rebekah Hren – SEIPS Senior Technician and PV System Designer – Solar Energy International Principal, CMP-4 of the National Electrical Code

Rebekah Hren is a founder of SEIPS and SEIE and has been teaching PV installation and design courses for Solar Energy International since 2007. A North Carolina native, her focus is quality control, Code-compliance, commissioning and maintenance for systems of all sizes, with a particular focus on utility-scale arrays. Rebekah is a licensed electrical contractor and NABCEP Certified PV Installation Professional. She frequently writes technical articles for Home Power and SolarPro magazines, and has co-authored several books: A Solar Buyer’s Guide for Home and Office, and The Carbon-Free Home. Rebekah spends a lot of her free time pondering the meaning of the National Electrical Code.

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