Improperly Seated Connectors: The most frequent culprit. Solar connectors (like MC4s) must "click" together fully. If they are left partially unlatched, rain and dirt get inside, causing corrosion and arcing.

Poor Crimping: If the metal pin inside the connector isn't crimped tightly onto the wire, it creates a high-resistance point. Resistance = Heat = Arcing.Loose Terminal Screws:** Screw terminals inside junction boxes or inverters can loosen over time due to thermal expansion (heating up and cooling down every day). A loose screw lets the wire bounce and spark.

Incorrect Wire Stripping: Stripping too much insulation off the wire leaves bare copper exposed. Stripping too little means the copper isn't making full contact with the terminal.

2. Component Failure & Aging

These happen over time as the system weathers the elements.(Corrosion: Moisture getting into connectors or junction boxes causes the metal to rust or oxidize. Corroded metal doesn't conduct electricity well, forcing the electricity to arc across the corroded spots.

UV Degradation: The sun's UV rays can make cable insulation brittle and crack over 5-10 years. Cracked insulation exposes the live wire inside.

Failed Components: Diodes inside the solar panels (which help manage shade) can fail and short circuit, creating excessive heat and potential arcing inside the panel junction box.

Thermal Cycling: The constant expansion (hot day) and contraction (cold night) of materials can wiggle connections loose over years.

3. External & Environmental Factors

These are causes coming from outside the system itself.

Animal Damage (Pest Attack): Rodents (squirrels, rats) and birds often chew through PV wires. They are attracted to the rubber insulation, and their teeth create the perfect gap for an arc.

Wiring Chafing: Cables that rub against sharp edges of the metal roof or aluminum racking can have their insulation slowly worn away, like sandpaper on wood.

Water Ingress: Water getting into conduits, DC isolators, or the inverter itself can create a path for electricity to jump to ground.

Mechanical Damage: Something as simple as a falling tree branch, hail, or someone walking on a panel can crack the glass and damage the internal wiring, causing a fault.

4. Faulty Materials

Rarer, but possible with cheap components.

Poor Quality Components: Using cheap, counterfeit connectors or cables that don't meet UV and temperature ratings. These fail much faster than the certified components Fonfich uses.

Manufacturing Defects: Microscopic burrs inside a new connector or a hairline crack in a panel's backsheet can become a problem years later.

Here is the explanation of why the inverter alone cannot stop all arcing, broken down into simple points. 

This is one of the most common questions we get.

If the inverter is the "brain" of the system, why can't it just shut things down to stop a fire?

The answer comes down to Location, Timing, and Physics.

1. Location: Where the Arc Happens Matters

Think of your solar system like a tree. The Inverter is the trunk, bolted to your wall. The Solar Panels are the leaves, way up on the roof. The DC Wire is the branch connecting the leaves to the trunk.

The Problem:

The inverter can only control what happens (inside itself)or immediately next to it. It cannot control what happens 50 feet away on the roof.              (Some cheaper inverter have internal AFCI but only work at a much higher voltaged ,some have set levals 1 to 9 but reconmeaned in the manufacture literature not to make changes to these setting, Why it that? what happens if these setting area changed, some time you can get nuisance tripping, the only way to cheack is with the manufacture, what is the best setting to use with what types of PV panels, as thier is so many on the market, they will ask how many panels in series and current of panels. but this is not this is not fail safe). if you are not 100% sure i would reconmend switch it ON within the inverter setting, something is better the nothing, 

If an arc happens INSIDE the inverter:

The inverter detects it instantly and shuts down. Problem solved.

If an arc happens ON THE ROOF (in a connector or wire):

The inverter might not even know it's happening until it's too late. The electricity is already arcing and burning up there. The inverter is just sitting there happily receiving power (or trying to).

2. The "Smoke Detector" Analogy

Imagine your kitchen is on fire. A smoke detector (the AFCI in the inverter) hears the crackling and yells for help.But the water sprinkler (the shutdown function) is only in the kitchen.If the fire is in the attic (the roof), the smoke detector in the kitchen might hear it and shut off the kitchen power, but the attic is still burning because the wires up there are still live.

3. The Three Types of Arcs (And Which One the Inverter Stops)

We mentioned the three types of arcs earlier. Here is which ones the inverter can actually handle.

Key Point:The inverter can only stop an arc that is "in line" with the flow of power (Series). It cannot stop an arc where power is jumping between two wires (Parallel) or leaking to the roof (Ground).

4. The "Sun is Always On" Problem

This is the biggest limitation. Solar panels make power whenever the sun is shining.There is no "off switch" for the sun.

Even if the inverter trips and turns off completely, the wires from the panels *to* the inverter are still 100% live with DC voltage.

If an arc starts on the roof while the inverter is off, it will keep burning because the panels are still pushing power through the arc.

5. So, How Do We Fix This? (Solutions)

Since the inverter can't do everything, we use other methods to ensure safety.

Rapid Shutdown Devices with (Arc Interrupter ) or (Smart Safety Protector)  These devices are unlike (SolarEdge Optimizer ) each little boxes attached to each panel monitoring panel DCvoltage singnal any interuptaion on the DC string will cut the power to the string,  where SolarEdge inverter shuts down, these boxes tells each panel to reduce its voltage to a safe, low level (like One volt per panel) example 22 panels in series = 22 volts, so if the inverter has more then one Mppt the votaged is doubled in some cases its trebled and more, In this case is it a safe isolation? in my eyes it not, or Maybe it is to some others, These devices will need monitoring control singnal device, 

6. How it works: 

After installing these little boxes on the back of  each panel, We install the AFCI monitor box but will need to be calibrated with your PV array, We use special pice of test equipmet at we can set small ach, this is then progromed in to the AFCI monitor PLC, with the normelly open contact within the monitor device a automatic switch at the roof closes, killing the total power of each string within the system. now we have a total power isolation. Sequence of the rapid shut down works in the same way as a safe isolation sequence. Shut Down (Turn Off  the AC supply) & Then (Turn Off DC Supplie) Start-up sequence (Turn On the DC supplie & then the AC supply.

so any part of our system that the AC supply is turns off if it from the main fuse board or by the mains incomer the system will shut down, only once the AC supply is intruduced after 3 mins the DC connects to the inverter the inverter wakes up and after 3 mins the inverter grid connects, with the new regs coming this april where fireman's switches need to be installed i dont this this is going to be an answer depending the location of this switch,    

Summary

Don't rely solely on the inverter to keep you safe. The inverter is your last line of defense, If these procation don't satify your bugit at least get your system test and maintained at least once a year.