4 Ways to Detect Cable Degradation That Causes Reduced Power Output

When a solar power system seems to be producing less electricity, the first things typically suspected are dirty panels, shading, equipment shutdowns, or weather differences. However, on-site cable deterioration and faults at connection points can also be behind reduced power output. Cables are the pathways that carry the generated electricity, and even without obvious visual abnormalities they can gradually suffer damaged insulation, loose terminals, increased contact resistance, moisture ingress, or degradation from ultraviolet radiation and heat. Such degradation does not always appear as a sudden major failure; it can manifest as variability in output, reduced generation only on specific circuits, sluggish performance on sunny days, or intermittent alarms.

Table of Contents

• Why suspect cable degradation when power output is low

• Point 1: Narrow down the abnormal range using power generation data and circuit differences

• Point 2: Check the appearance for discoloration, cracks, and sagging

• Point 3: Inspect connection points for overheating, loosening, and moisture ingress

• Point 4: Assessing deterioration risk from environmental conditions and construction history

• Decisions to Avoid When You Discover Cable Degradation

• Recording and ongoing monitoring to prevent declines in power generation

• Summary: Narrow down cable degradation early and assess it together with on-site records

Reasons to suspect cable degradation when power output is low

When the power output of a solar photovoltaic system is low, it's dangerous to attribute it to a single cause. There are multiple factors that can reduce output, such as days with low solar irradiance, high temperatures, dirty panel surfaces, or temporary shading of the surrounding area. Cable degradation is often overlooked because, unlike large components such as panels or racking, cables are usually hidden in wiring routes, cable tie points, inside junction boxes, or behind equipment. Because deterioration progresses gradually in places that are hard to inspect visually, it can be difficult to notice until a clear shutdown or a major alarm occurs.

The role of cables is to safely carry the electricity generated by solar panels. If increased resistance or poor contacts occur along this path, the flow of electricity can become unstable, which may lead to reduced power generation and losses. Especially on the DC-side wiring, abnormalities can appear at the circuit level where multiple panels are connected. If only one circuit shows low power output, if the current does not rise even when it is sunny, or if readings drop unnaturally at certain times of day, then not only the individual panels but also the wiring routes need to be checked.

Cable deterioration does not always appear in an obvious form like a break. Causes are varied: fine cracks in the jacket, stress at bend points, tightening by cable ties, loosened terminals, moisture ingress, damage by animals, contact during grass cutting, abrasion against racking or the ground, and so on. When these factors combine, they can lead not only to reduced power generation but also to safety risks. When you receive a report of low power output, it is important not just to look at the generation data, but to take the perspective of inspecting the entire path through which electricity flows.

Also, cable abnormalities can appear differently depending on the season and weather. If anomalies occur only after rain, power output does not increase during high temperatures in summer, readings fluctuate on windy days, or alarms trigger during periods of high humidity in the mornings and evenings, it is worth checking the condition of the connections and sheathing and the fastening of the wiring. To find the cause of low power generation quickly, rather than suspecting the entire installation at once, it is important to check the data, appearance, connections, and environmental conditions in that order.

Point 1: Narrow down the anomaly range using power generation data and differences between circuits

The first step in detecting cable degradation is to narrow down the area showing anomalies using generation data. You can go to the site and inspect each cable one by one, but in a large power plant this takes time and increases the chance of overlooking problems. First, check daily, hourly, and circuit-level generation and current values to determine which area is showing an unnatural drop. If the whole system is similarly low, weather, solar irradiance, temperature, or overall system control may be involved. Conversely, if only a specific circuit is consistently low, you can focus your inspection on the panels, cables, connections, and protective devices included in that circuit.

To correctly assess the phenomenon of low power generation, it is important not to judge solely by simple daily totals. On cloudy or rainy days the overall generation falls, so those days may not be suitable for judging cable degradation. If you compare, using days with similar solar irradiance conditions, circuits with similar orientation or tilt within the same installation, or historical data from the same period will make it easier to detect abnormalities. If, on sunny days, other circuits are generating normally but only a specific circuit shows low current, candidates include increased resistance in cables or connections, poor contact, partial open-circuit, or terminal issues.

Changes by time of day are also important. Whether levels remain low from the morning, dip only around midday, or become unstable in the evening will change which areas you should suspect. For example, if a specific circuit is low throughout the day, persistent connection faults or cable damage may be suspected. If the gap widens only during periods of strong sunlight, heat may be degrading the condition of connection points. If it drops only after rain, focus inspections on connection points prone to moisture ingress or on areas with damaged insulation.

When reviewing power generation data, also check whether an anomaly occurred only once or is recurring. If the drop is temporary, influences such as clouds, shading, work stoppages, or communication issues can be considered. However, if the same circuit experiences drops repeatedly, or if the magnitude of the drops is gradually increasing, this is grounds to suspect equipment deterioration. Because cable degradation can progress, you cannot conclude that there is no current problem just because there were no problems in the past. Even small but persistent differences should be reflected in inspection plans as soon as possible.

What on-site personnel should be careful about is not dismissing a drop in power generation as merely "dirty panels" or "bad weather." Of course, soiling and weather are important factors, but when differences between circuits are apparent under the same conditions, it is necessary to isolate problems in the electrical path. To detect cable degradation, it is effective to examine generation data not as an overall site average but in detail at the circuit, junction-box, and equipment levels. By narrowing the scope with data before conducting on-site checks, inspection priorities become clear and the time required to pinpoint the cause can be reduced.

Point 2: Check the appearance for discoloration, cracks, and sagging

After narrowing down the abnormal range using power generation data, the next thing to check is the appearance of the cables. Cables are exposed to outdoor environments, so they are affected by ultraviolet radiation, heat, rain, wind, snow, humidity, sand and dust, and contact with vegetation. Changes in appearance are not necessarily the direct cause of reduced power output, but they provide an important clue for identifying the onset of degradation. In particular, if there is discoloration of the insulation, cracking, hardening, blistering, abrasion, exposure, sagging, excessive bending, or poor fastening, you need to check whether these have led to any electrical abnormalities.

Discoloration can be a sign of exposure to ultraviolet light or heat. If parts are partially faded in color, the surface appears powdery, or the area looks noticeably more heat-damaged than its surroundings, the coating may be deteriorating. When the coating deteriorates, it becomes more susceptible to moisture and dirt from the outside, which can lead to a decline in insulating performance. However, you should not immediately conclude that discoloration alone is the cause of reduced power generation; it is important to judge it together with the surrounding mounting conditions, the condition of connection points, and trends in generation data.

Cracks and scratches are appearance abnormalities that require greater attention. If fine cracks are visible on the cable surface, the bent or bundled sections may be under stress. Cases where the jacket is worn and the interior is close to being exposed, where the cable is rubbing against the corner of a rack, or where it is in contact with the ground or weed-control materials should be considered for prompt action. In particular, wiring that rubs in the same spot every time it sways in the wind, or wiring whose ties have loosened and sagged, is likely to suffer progressive damage over time. If such appearance abnormalities are found on circuits with low power output, raise the inspection priority and check them.

Do not overlook sagging and poor fastening. If a cable sags down to a position close to the ground, it becomes more susceptible to rainwater, mud, grass trimmers, animals, and falling objects. Be careful as well when a cable is pressed tightly against a rack or bent along a sharp edge. Wiring not only needs to carry electricity but must be secured so it can be used stably over a long period. If fastening is insufficient, repeated movement from wind or temperature changes places strain on connection points and bend areas. As a result, this can progress to poor contact or a condition approaching a broken conductor.

In visual inspections, it's important to examine not only the cables themselves but also their surrounding environment. Weeds overgrowing and entangling the cables, fallen leaves and soil accumulating around wiring, signs of intrusion by birds or small animals, and poor drainage causing prolonged wet conditions — these situations can accelerate cable degradation. Rather than scrambling to check after a drop in power generation has occurred, record these changes with photos during routine inspections so you can more easily compare with past conditions when an abnormality appears.

The important thing in visual inspections is not to judge solely by the immediate impression at the site when you find an abnormality. You should determine which circuit and which position it is, whether there is similar degradation nearby, and whether it matches the range of decline shown in the power generation data. Visible deterioration may not yet be reflected in power output, and conversely low power output may not be apparent from appearance. That is why visual checks need to be used in combination with data review. To detect cable degradation, it is important to note visible abnormalities while keeping open the possibility of unseen electrical faults.

Point 3: Inspect connection points for overheating, looseness, and moisture intrusion

When you suspect cable degradation, pay particular attention to the connection points. Even if there is no obvious damage along the cable, poor contact at terminals, junction boxes, equipment input ports, branch points, connectors, etc., can lead to reduced power output. Connection points are prone to concentrated load within the electrical path, and their condition can change due to insufficient tightening during installation, loosening over time, vibration, thermal expansion, moisture ingress, and dirt accumulation. If any circuit shows low power output, it is important to carefully inspect not only the cable itself but also the connection points.

When contact resistance increases, heating may occur at connection points. Heating creates losses and can accelerate deterioration of nearby components. Because the effect is more likely to appear during periods of high generation current on sunny days, checking the condition of connections is useful if generation data show a decrease or unstable changes around midday. However, it is dangerous to touch energized equipment carelessly. Thermal checks and electrical measurements must be carried out by personnel who have the required qualifications and follow procedures to ensure safety. Field personnel should not touch equipment to make a judgment; instead, they should record locations suspected of abnormalities and arrange for appropriate inspection.

Looseness can also cause a decrease in power generation. If terminal tightening is weak, the connection condition has changed with age, or the wiring is under tensile stress, the flow of electricity can become unstable. Even if the connection appears intact externally, the internal contact may be insufficient. If only a specific circuit shows low readings, alarms occur occasionally, fluctuations happen on windy days, or performance improves for a while after inspection but then declines again, it is worth checking the fastening condition of the connections and the tension of the wiring.

Moisture ingress is a factor that tends to cause problems after rainy weather or during periods of high humidity. If waterproofing at connection points is insufficient, if cable entry direction is poor, or if degraded sheathing or connections allow moisture to enter, it can lead to insulation failure or poor contact. If power output becomes unstable only after rain, alarms increase during humid seasons, or there are traces of condensation or water droplets inside junction boxes, suspect the influence of moisture. Because it may not be apparent from an external visual inspection, comparing recorded occurrence timing with the site’s weather history makes it easier to narrow down the cause.

When inspecting connection points, pay attention to changes such as scorch marks, discoloration, deformation of resin parts, odors, accumulation of dirt, and corrosion. These can be clues that the area has previously been affected by heating or moisture. When investigating the causes of low power generation, it is important to consider not only current readings but also what kinds of loads were applied in the past. Abnormalities in connection points may appear as minor changes, but if left unaddressed they can spread beyond generation losses to equipment maintenance problems. For safety reasons as well, suspicious areas should be promptly referred for professional inspection.

Point 4: Assessing deterioration risk from environmental conditions and construction history

To detect cable degradation, it is important not only to examine the current appearance and power generation data, but also to consider the environment the cables have been exposed to and the installation history. Even systems that have been in service for the same number of years can deteriorate at different rates depending on the installation environment. Locations continuously exposed to strong sunlight, areas with strong winds where cables are prone to sway, places where humidity tends to accumulate, sites affected by snow accumulation or freezing, locations near the sea that are susceptible to salt exposure, and places where vegetation or soil is likely to come into contact all impose greater stress on cables and connection points. For systems with low power output, it is necessary to organize not only the locations of abnormalities but also the environmental context in which the system is installed.

Installation history is also an important factor. If there are records of having changed wiring routing, replaced junction boxes or equipment, carried out additions or renovations, disturbed the surroundings during mowing or civil engineering work, or performed emergency measures after a typhoon or heavy rain, check whether deterioration or connection faults remain in those areas. Even if there were no problems immediately after the work, parts that are not adequately secured or that are bent sharply can develop faults over time. Comparing when the decline in power output began with the installation history makes it easier to narrow down potential problem locations.

The design of wiring routes and the methods used to secure them also affect long-term degradation. If cables are not properly supported, they can move due to wind and temperature changes, placing strain on the connections. Attention is also required when there is insufficient bend radius or when weight is concentrated at a single point. Conditions such as cable ties that have deteriorated and broken, or conversely are tightened so much that they leave marks on the jacket, or cables contacting mounting racks or metal parts, can cause future damage. Even if there are no symptoms such as reduced power generation, it is desirable to record such conditions as items for preventive maintenance when they are found.

The effects of nearby work are also often overlooked. Mowing, snow removal, drainage cleaning, panel washing, repairs around the racking, and other tasks are carried out around power generation equipment. During such work, cables can be contacted, wiring can be snagged, or fasteners can come off. If a low power output condition begins after work, cross-check the work area with the wiring routes. Photographic records before and after work are useful, especially because wiring close to the ground or hidden by grass is easy to miss when damaged.

By reviewing environmental conditions and installation history, the cause of reduced power generation can be regarded not as an isolated failure but as an equipment management issue. Simply replacing a cable because it has deteriorated may only lead to recurrence as long as the same environmental conditions or fastening methods remain. Clarifying why deterioration occurred at that location, why only that circuit showed a decline, and why the symptoms appeared at that time will help prevent recurrence. It is precisely when power output is low that it is important not only to recover the numbers but also to investigate the underlying factors that caused the deterioration.

Decisions to avoid when you discover cable degradation

When you find an anomaly that appears to be cable degradation, what you want to avoid is assuming "it's only slightly worn on the surface, so it's not a problem." When the drop in power generation is still small, its impact on the site can be difficult to discern. However, deterioration of the sheath or loosening of connections can progress, and if left unaddressed, power generation losses may spread. Even for small anomalies, it is important to record power generation data, circuit information, location, and time of occurrence, and to have a professional inspection carried out when necessary.

Conversely, you should avoid concluding that an observed visual abnormality is "the cause of the reduced power generation" based solely on its appearance. There are multiple possible causes for low power generation, such as shading, soiling, equipment control, communication faults, weather conditions, panel defects, and the operation of protective devices. Even if you find a cable with visible deterioration, you need to verify by measurement and comparison how much it actually contributes to the reduction in power generation. In on-site decision-making, it is important to keep an open mind about possibilities while prioritizing based on data.

Care is needed when deciding to rely solely on temporary measures. Even if provisional securing or temporary repairs make readings appear to return to normal, the problem will recur if the root cause remains. Especially when there are signs of moisture ingress or overheating, repairing only the visible parts can leave internal deterioration. Continuing operation without performing safety checks may lead to problems more serious than a drop in power generation. Because power generation equipment is intended to operate for long periods, it is necessary to consider short-term recovery and long-term integrity separately.

You should also avoid allowing on-site personnel to perform hazardous checks alone. Live cables and connections carry risks of electric shock and short circuits. Checks such as detecting overheating, verifying insulation condition, and confirming terminal tightness must be carried out by personnel who understand the equipment condition and procedures and have implemented appropriate safety measures. It is natural to want to quickly determine the cause of low power generation, but hastily touching equipment is not necessarily the correct response. What can be done on-site is to record the extent of the abnormality, organize photos and data, and link these to appropriate inspections.

Judging cable deterioration requires layering multiple pieces of information rather than relying on a single impression. Narrow down the abnormal range using power generation data, visually inspect for signs of deterioration, check the condition of connections, and cross-check environmental conditions and history. By following this flow, you can reduce unnecessary component replacements and misdirected inspections, and focus on the necessary actions. Responding to a drop in power generation is not about guessing the cause but about building evidence to narrow down the possibilities.

Recording and Ongoing Monitoring to Prevent a Decline in Power Generation

To prevent reductions in power output caused by cable degradation, it is important not to inspect only when anomalies occur, but to build up regular records. Keeping generation data, inspection photos, work histories, weather conditions, and changes in the surrounding environment provides reference data for comparison when you feel the power output is low. If the past normal condition is unknown, it becomes difficult to judge whether the current state is abnormal or an inherent characteristic. This is especially important at large power plants, where many similar cables exist, so recording them together with location information and circuit information is essential.

Photographic records help manage cable degradation. Regularly photographing the cable jacket condition, the state of bundling and ties, areas around junction boxes, clearance from the ground, contact with vegetation, and drainage conditions makes it easier to track the progression of deterioration. If you can photograph the same spot from the same angle, it becomes easier to compare discoloration, sagging, and deterioration of mounting hardware. When a circuit shows low power output, reviewing past photos of the area around that circuit can help estimate when the change began.

When recording power generation data, comparing on a per-circuit basis is important, not just the total generation. If you only look at the total output of the entire facility, small declines in a particular circuit can be masked by the overall numbers. To find abnormalities early, compare circuits under the same conditions and check whether differences are widening. In addition to monthly generation totals, looking at time-of-day data on sunny days makes it easier to pick up signs of overheating or poor contact.

Keeping records after inspections is essential. Record which cables were checked, which connection points were inspected, what abnormalities were found, and how power generation changed after corrective actions. Without a before-and-after comparison, you cannot determine the effectiveness of inspections or repairs. Even if power generation recovers, you need to ascertain whether the cause has truly been resolved or whether the improvement was only temporary due to other factors. Keeping records speeds up decision-making if a similar drop occurs again.

For ongoing checks, it is important not to fix inspection frequencies and priority areas, but to review them based on the condition of the equipment. Locations where deterioration has been found, areas with high humidity, places with frequent grass-cutting operations, and sites that have experienced connection faults in the past should be checked more frequently than others. To detect low power output quickly, it is effective not only to inspect the entire installation uniformly but also to focus inspections on high-risk areas.

Summary: Narrow down cable degradation early and assess it in conjunction with on-site records

Cable degradation that leads to reduced power output does not always appear suddenly as an obvious failure. It can begin with small signs such as only certain circuits producing low output, readings that don’t rise on sunny days, instability after rain, discoloration or signs of heating around connection points, or slack or chafing in the wiring. When you notice low power output, it’s important to look not only at panel soiling and the weather but also at the cables that carry electricity and their connection points.

The basic method for detection is to narrow down abnormal areas using power generation data, confirm visual signs of degradation, check connection points for heating, looseness, or possible moisture ingress, and make a judgment by cross-referencing environmental conditions and installation history. Rather than drawing a conclusion from any single factor, combining multiple pieces of information increases the accuracy of identifying the cause. Because cable degradation affects not only power output but also safety, if you find a suspicious spot, do not handle it forcefully; follow the appropriate procedures to obtain a professional inspection.

Also, responding to reduced power generation is not something that can be completed with a single inspection. By maintaining routine photo documentation, comparing circuit-by-circuit data, organizing work histories, and tracking areas of deterioration, you can achieve early detection of abnormalities and prevent recurrence. If the site’s condition is properly recorded, you can make decisions based on evidence rather than intuition when generation is low.

To detect cable degradation in solar power generation equipment, management that links visible on-site information with generation data is essential. By organizing inspection records, location information, and on-site photos while tracing the causes of reduced power output, you can reduce overlooked anomalies and make it easier to proceed from on-site verification to decisions on corrective actions. It is important to continuously check each installation’s wiring routes, connection points, surrounding environment, and past work history, and to establish a management system that can identify low power output conditions early.