Optimizing Cable Management To Ensure Safety And Efficiency In Utility Scale PV Systems

Utility-scale photovoltaic (PV) systems typically generate several megawatts (MW) of electricity and are key contributors to green energy and sustainability. Each MW requires about 2,900 solar panels spread over several acres of land, one or more inverters and controllers, plus grid connection equipment.

Linking all those elements into a PV system can require miles of power and monitoring cabling, and tens of thousands of cable management components. If not properly implemented, cabling and cable management components can literally become the weak link reducing efficiency, limiting availability, increasing safety hazards, and driving up installation and operational costs.

Safe and efficient cable management installations

Designing safe and efficient cable management installations is complex

Designing safe and efficient cable management installations is complex. It includes cable cleats for short circuit protection of power cabling, the absence of voltage testers to protect personnel servicing the installation, edge clip cable ties for reliable signaling and monitoring connections, and compression lug connectors for power and grounding.

Additionally, these components must meet various international standards like cable cleats that must adhere to IEC 61914:2015 to ensure they can withstand a ground fault, absence of voltage testers that must operate as required by the National Fire Protection Association (NFPA) and UL and CSA safety standards and general requirements for solar components to withstand outdoor conditions as defined in IEC 61215 for PV installations.

This article provides a dive into the elements in a utility-scale PV installation focusing specifically on the large number of cable management components needed, details some of the related international safety standards, and reviews the requirements for operation in harsh environments and cost-effective installation. Throughout the discussion, exemplary products from Panduit are highlighted.

Growing importance of BOS

In PV installations, the balance of system (BOS) includes everything other than the PV panels, like racks, cables, cable management, inverters, and other system devices, plus labor and software. As PV panel technology has improved, panel prices have dropped faster than the prices for BOS components.

According to an analysis by the International Renewable Energy Agency (IRENA), 62% of the cost reduction in PV installations was due to falling prices for PV panels and inverters.

Falling costs for PV panels and inverters

The falling costs for PV panels and inverters have spotlighted BOS components

The falling costs for PV panels and inverters have spotlighted BOS components. According to IRENA, BOS is a growing percentage of the cost of PV installations, rising from 58% in 2007 to 80% in 2017.

At the same time, boosting the distribution bus to 1 kVDC and higher has increased the importance of BOS components relative to system efficiency and safety. Going forward, BOS components will be increasingly important to drive cost reductions and operational improvements, including increases in safety and efficiency in grid-scale PV systems.

Cable management is a critical aspect of the BOS

Cable management is a critical aspect of the BOS in grid-scale PV systems. It has significant impacts on safety, cost, and efficiency. Cable cleats are a good example of the benefits of optimized cable management. They provide short circuit protection for power cables.

Without proper protection, the high currents experienced during a short circuit can heat the conductors, leading to the possibility of fires or explosions. Short circuit currents also lead to large electromechanical stresses on power distribution cabling.

Cable cleats must meet requirements of IEC 61914:2015

For maximum safety, cable cleats must meet the requirements of IEC 61914:2015. The maximum electromechanical stress is experienced during a short circuit event after about 5 milliseconds (ms). That’s well before the 60 to 100 ms required for circuit protection devices like circuit breakers to react.

IEC 61914:2015 specifies a short circuit test duration of 100 ms for cable cleats

IEC 61914:2015 specifies a short circuit test duration of 100 ms for cable cleats, sometimes called cable clamps. Panduit uses simulation software when designing its cable cleats and then subjects them to a live short circuit fault to confirm compliance with IEC 61914:2015.

IEC 61914:2015 is about more than short circuit protection; it includes provisions for:

• Temperature rating
• Resistance to flame propagation
• Corrosion resistance
• Axial load testing
• Lateral load testing
• Impact resistance
• UV resistance

Panduit’s Trefoil cable cleats

Panduit’s Trefoil cable cleats are made using 316L stainless steel, also called marine grade stainless steel, with models that accommodate cables with diameters from 20 to 69 millimeters (mm).

For example, model CCSSTR6269-X can handle 62 to 69 mm cable diameters. These cable cleats can be installed after running the cable using a Panduit mounting bracket or before running the cable by installing the cleat directly to the cable tray rung through a fixing hole using an M8 bolt.

The complexities of the electromechanical forces experienced during a short circuit and the strict performance demands of IEC 61914:2015 combine to make identifying the needed cable clamp a burdensome mathematical exercise.

Cable Cleat kAlculator app

Panduit offers the Cable Cleat kAlculator app that recommends IEC 61914:2015 short circuit solutions from over 60 Panduit cable cleat products to speed the selection process. Using the kAlculator app reduces cable clamp selection to a simple three-step process:

• Select the cable layout.
• Input the cable diameter.
• Input the peak short circuit current.

The app provides component and spacing recommendations.

Power and grounding

Copper compression lug connectors can provide efficient connectivity

In addition to cable clamps for power and ground cables, utility-scale PV installations require power and ground connectivity. Copper compression lug connectors can provide efficient connectivity, and Panduit offers the only copper compression lugs that meet the Network Equipment Building Systems (NEBS) Level 3 requirements as tested by Telcordia Technologies.

Meeting NEBS Level 3 assures users that Pan-Lug compression connectors can provide reliable performance in applications like utility-scale PV that demand minimal service interruptions over the lifespan of the equipment.

Utility scale PV installations

Designers of utility scale PV installations can turn to Panduit’s flex conductor, two-hole, standard barrel connectors that can be used with flexible, extra-flexible, and code-stranded copper conductors to provide efficient and reliable power and ground connectivity.

For example, the model LCDX1/0-14B-Xis rated for use with #1 American wire gauge (AWG) size cables and has two 0.25 inch (in) stud holes on 0.75 in spacing.

Common features of all Pan-Lug compression connectors include:

• UL Listed and CSA Certified to 35 kV and temperature rated to +90°C.
• Internally beveled barrel ends simplify conductor insertion.
• Inspection window to ensure complete insertion.
• 99.9% pure copper body with tin plating to inhibit corrosion.

Clips and ties

In addition to power cabling, utility-scale PV installations can include miles of wiring for control and monitoring functions. If not properly specified and installed, the cable clips and ties used for cable management can reduce system reliability and increase installation and operating costs. General-purpose cable clips are not designed for long-term exposure to sunlight and outdoor weather conditions.

If used in PV installations, general-purpose non-ultraviolet (UV) resistant plastic clips and ties can become brittle and require regular replacement. Also, exposure to salt can corrode metal clips, damaging the galvanized edges of PV panels. In both cases, maintenance costs can significantly increase, and reliability can suffer.

Edge clip cable ties

Instead of using general-purpose clips and ties, PV system designers can turn to edge clip cable ties

Instead of using general-purpose clips and ties, PV system designers can turn to edge clip cable ties like the model CMSA12-2S-C300 from Panduit, which is made with heat-stabilized weather-resistant Nylon 6.6 and zinc-plated metal clips and tested to IEC 61215 standards for outdoor PV installations.

Additional features include:

• UL94V-2 flammability rating.
• Rated for continuous operation from -60°C to +115°C.
• Meets EN45545-2 fire protection requirements according to the classification R22:HL3 and R23:HL3 criteria.
• UV weathering life expectancy of 7 to 9 years.

These edge clip cable tie mounts secure wiring bundles without adhesives or drilling. They are preassembled with a cable tie and a clip that can be mounted to panel edges with thicknesses from 0.7 millimeters (mm) to 3 mm, depending on the model. The metal clip provides a secure hold and can be installed by hand without needing tools.

Designed for rapid installation

They are designed for rapid installation. Compared with a traditional zip tie that can take about 21 seconds to install, these edge clips can be installed in 11 seconds, saving 10 seconds per clip. That adds up.

In a typical utility-scale PV installation with 2,900 PV panels per MW and three clips per panel, the labor savings can be 24.17 hours, or 47% (50.75 hours to install conventional zip ties versus 26.58 hours to install the Panduit solar cable edge clips).

Servicing grid-scale PV

When servicing grid-scale PV installations, especially when servicing the power distribution cables, a voltage verification test is required by safety regulations to validate the absence of hazardous voltages.

Absence of voltage (AVT) testing using handheld portable test instruments is complicated

For example, National Fire Protection Association (NFPA) regulation NFPA-70E requires that high voltages inside equipment cabinets be verified absent before maintenance personnel can perform any work inside the cabinet.

Absence of voltage (AVT) testing using handheld portable test instruments is complicated, fraught with possible inaccuracies, and time-consuming. VeriSafe AVTs from Panduit provide an automated solution that test for hazardous voltages inside an equipment cabinet before opening the door.

Using an automated test solution brings several benefits, including:

• Reliability improves safety and reduces risk.
• Simplicity increases productivity and ensures compliance with safety regulations.
• Flexibility enhances implementation.

VeriSafe AVTs

VeriSafe AVTs, like the model VS-AVT-C02-L03, consist of several elements, including an isolation module that mounts inside the enclosure and connects redundant sensor leads to high-voltage areas, as well as neutral and ground lines. The isolation module securely connects to a battery-powered indicator module that’s visible when the enclosure door is closed and cables that connect the two modules.

When initiating a test using a VeriSafe AVT system, the test button on the indicator module is pressed

When initiating a test using a VeriSafe AVT system, the test button on the indicator module is pressed, and the system performs a self-test. Red LEDs and testing stops indicate any failure of the self-test. If the self-test is passed, the isolation module tests for voltages and ground faults.

The final step is for the AVT to perform a second self-test. Only if the second self-test is passed and there is no voltage present will the AVT indicate that it’s safe for personnel to open the cabinet and work on the system.

Summary

BOS components account for an increasing percentage of the cost of utility-scale PV installations. Cable management is an important aspect of BOS design, and the selection of optimized cable clamps, power and ground lugs, and edge clip cable ties can significantly enhance the operation and safety of those installations.

The addition of automated absence of voltage testing supports ongoing maintenance activities, increasing safety and reducing operating costs.