Arch Fault – DC Protection. Prevent fires.

There is as always some confusion with DC protection and this morning was no different, when on my feed appeared confusion on a DC breaker mainly due to the wiring diagram and the use of + and -.
the groups connotations went on to breakers and isolation of the PV which is a DC circuit and DC isolator fires which I had posted about some years before.

Solar DC Arc Fault Detection: IEC, NEC and Requirements

Solar systems use direct current (DC) and are susceptible to a specific type of fault called a DC arc fault. These faults can be dangerous as they often occur in hidden areas and can cause fires. To address this, there are guidelines and requirements from international and national bodies for DC arc fault detection.

Here’s a breakdown of the relevant acronyms:

• AFCI (Arc Fault Circuit Interrupter): This term is typically used for AC applications. While similar in concept, there are some key differences for DC systems.
• AFDD (Arc Fault Detection and Disconnection Device): This term is specifically used for DC applications like solar systems.

Standards and Requirements:

• IEC (International Electrotechnical Commission): The IEC standard IEC 62109-2 specifically addresses photovoltaic (PV) systems and recommends the use of AFDDs for DC arc fault protection.
• NEC (National Electrical Code): The NEC, enforced in the United States, doesn’t currently mandate AFDDs for all solar systems. However, Article 690.11 of the 2023 NEC does require rapid shutdown of DC circuits for certain solar installations. In some cases, AFDDs can be used to achieve this rapid shutdown.

Important Points:

• While not universally mandated, IEC and some national regulations are increasingly recognizing the importance of DC arc fault detection for solar safety.
• There are limitations to AFDDs. Inverters with built-in arc fault detection may not identify all types of DC arc faults.

Here are some resources for further reading:

• Implementing Arc Detection in Solar Applications: Achieving Compliance with the new UL 1699B Standard [PDF] : https://www.ti.com/video/6314124593112
• Solar fires – DC arc faults: https://www.acsolarwarehouse.com/products/category/clearance/
  
  

Arc Fault Detection (AFD) in DC circuits is designed to protect against arc faults, which are unintentional electrical discharges that can generate high temperatures and potentially cause fires. AFD devices monitor the circuit for the unique electrical signatures of arc faults. When detected, they automatically trip the circuit to prevent damage.

Here’s a simplified explanation of how AFD works:

1. Monitoring: AFD devices continuously monitor the waveform of the electricity flowing through a circuit using microprocessor technology¹.
2. Detection: They analyze these waveforms to identify any unusual patterns or signatures that indicate an arc fault².
3. Interruption: Upon detecting an arc fault, the AFD device quickly interrupts the power supply to the affected circuit, mitigating the risk of fire³.

AFD devices are particularly important in DC circuits, such as those used in solar panel installations, because DC currents do not cross zero volts as AC currents do, making arcs more sustained and potentially more dangerous in DC systems. By implementing AFD, the safety of these systems is significantly enhanced.

DC ISOLATORS

In the UK, the position on DC isolation for solar is a bit nuanced. Here’s the breakdown:

• Requirement: There’s currently no legal mandate in the UK to install DC isolators for all domestic solar photovoltaic (PV) systems.
• Guidance: However, some industry guidance and best practices recommend including DC isolation for safety reasons.
• Reasons for DC Isolation:
  • Emergency isolation: A DC isolator allows for the complete shutdown of the DC circuit from the solar panels to the inverter. This can be crucial for firefighters or during maintenance work.
  • Safety during maintenance: Isolating the DC circuit minimises the risk of shock during maintenance or troubleshooting.
• Potential Concerns about DC Isolation:
  • Misunderstandings: Some argue that DC isolators can be accidentally left open, interrupting power generation. With proper training and labeling, this risk can be mitigated.
  • Cost: Adding a DC isolator increases the system cost slightly.

Here are some resources to explore further:

• MCS (Microgeneration Certification Scheme): While not a legal requirement, MCS is a highly regarded certification scheme for solar installers in the UK. The MCS installation standard MCS 001: encourages the use of DC isolation for safety.
• Electrical Competent Person Scheme: When it comes to electrical work, including solar installations, the UK follows the Electrical Competent Person Scheme. This scheme emphasizes the importance of adhering to best practices for safety, which often includes DC isolation.

In summary:

• DC isolation for solar PV systems in the UK is not mandatory but recommended by some industry bodies due to safety benefits.
• Consult with a qualified electrician or MCS certified installer to understand the best practices for your specific solar installation.

DC Isolators and Solar Fires: A Balancing Act

The relationship between DC isolators and solar fires is a complex one with arguments on both sides. Here’s a balanced view of the information:

DC Isolators and Safety Benefits:

• Emergency Shutdown: DC isolators allow for a complete shutdown of the DC circuit, essential for firefighters and maintenance personnel. This reduces the risk of electric shock and facilitates safer intervention during emergencies.

Potential Drawbacks of DC Isolators:

• Fire Risk: Studies like the UK government report (https://www.telegraph.co.uk/business/2023/06/12/britain-fires-up-coal-plant-weather-too-hot-solar-panels/) suggest poorly designed or installed DC isolators can be a fire hazard. This can occur due to:
  • Environmental factors: Exposure to sun and water ingress can lead to corrosion and overheating in the isolator, increasing fire risk.
  • Installation errors: Improper installation can create loose connections or arcing faults, which can ignite nearby materials.

Arguments Against DC Isolators:

• Redundancy: Some argue that modern inverters have built-in DC arc fault detection and rapid shutdown capabilities, potentially making DC isolators redundant.
• Misuse: Accidental left-open isolators can interrupt power generation.

Arguments For DC Isolators:

• Safety First: Proponents highlight the importance of a physical disconnect for emergency response and maintenance, regardless of inverter capabilities.
• Best Practices: Industry bodies like MCS in the UK still recommend DC isolation for overall safety.

Finding Balance:

• Quality and Installation: Properly designed, installed, and maintained DC isolators minimise the fire risk while offering safety benefits.
• Alternative Approaches: Systems with microinverters or optimisers might not require DC isolators due to lower DC voltage levels.

There are a couple of reasons why some DC isolators have been linked to solar fires:

• Environmental factors and poor quality: Exposure to sunlight and water ingress can damage DC isolators, particularly those that are poorly designed or manufactured. This damage can lead to corrosion, overheating, and ultimately fire.
• Installation errors: If a DC isolator is not installed correctly, it can create loose connections or arcing faults. These faults can generate sparks and high temperatures, which can ignite nearby flammable materials.

Here’s a breakdown of the contributing factors:

• Sun exposure: Over time, prolonged exposure to sunlight can degrade the materials within a DC isolator, making them more susceptible to issues like overheating.
• Water ingress: If water gets inside the isolator, it can cause corrosion of electrical components. This corrosion can increase resistance, leading to heat buildup and potential fire.
• Loose connections: Improper installation can leave connections loose or faulty. These loose connections can create arcing faults, where electricity jumps across a gap instead of flowing smoothly. Arcing faults generate significant heat, which can ignite surrounding materials.

It’s important to note that not all DC isolator fires are due to these factors. However, they have been identified as significant contributors in some cases.

Here are some additional points to consider:

• Regulations: In some regions, like Australia, DC isolators were previously mandatory for solar installations. However, due to concerns about fire risk, the requirement has been relaxed in some areas (https://www.pv-magazine.com/2023/09/15/dc-isolators-trigger-sharp-increase-in-solar-fires-in-australia/).
• Alternatives: In some cases, alternative approaches like using microinverters or optimizers can eliminate the need for a DC isolator entirely, as these systems operate at lower DC voltage levels.

Conclusion:

The decision to use a DC isolator involves weighing safety benefits against potential drawbacks. Here are some tips:

• Consult your installer, we always use DC Isolators.
• Ensure proper design, installation, and maintenance of the DC isolator.
• Consider the specific features of your inverter and system layout.

CLEAR as mud?

Every story has two sides, and those who have worked with DC for years, understanding its problems and risks, know that caution and risk accompany most things. A joint in a circuit introduces risk, as does the installation of an AFD or Isolator (or both), which also increase resistance. As most inverters include AFDs, it’s important to look in the right places and be aware of their limitations in function.

Installation devices such as DC isolators offer benefits and operate in various ways. For instance, a DC isolator allows for the PV system to be shut down in case of a general fault or during maintenance. However, DC isolators require active maintenance.

Most local electrical specialists lack the skills or willingness to properly test, check, and inspect solar installations. I would estimate that about 90% of installers are also unaware of how to do so. The crux of the matter is that many AC electricians are attempting to capitalize on solar energy without a solid understanding of AC systems, let alone DC. Without years of experience, they will likely overlook most faults and issues and remain oblivious to potential problems at the time of installation or during maintenance.

Maintenance:

To ensure optimal performance and safety, solar installations require some regular maintenance checks. Here’s a breakdown of the key checks you can perform:

Visual Inspection (Every 6 months): ( in Spring is a good time)

• Panels: Look for cracks, discoloration, debris, or signs of animal nesting. including connections.
• Roof and Mounting System: Check for loose tiles, damaged flashing, or any corrosion on mounting hardware.
• Wiring: Inspect for any fraying, burning, or damage to the electrical cables.
• Inverter and Other Equipment: Look for any physical damage, leaks, or signs of overheating on the inverter and other electrical components.

Performance Monitoring (Ongoing):

• Electricity Production: Monitor your system’s energy production data. Significant drops compared to historical data or expectations might indicate performance issues.
• Inverter Status: Check the inverter’s status lights and any error messages displayed as well as logged faults.

Less Frequent Checks (Professional recommended every 1-5 years):

• Electrical Testing: A qualified electrician can perform specialised tests to check for proper grounding, insulation resistance, and DC arc faults.
• Cleaning: Depending on your location and environment, professional cleaning of the panels might be necessary every few years to remove dust, bird droppings, or other debris that can impact efficiency.

Here are some additional tips:

• Keep a maintenance log: Record your observations and any actions taken during inspections.
• Consult your system manual: The manufacturer’s manual might have specific recommendations for your solar system.
• Consider professional maintenance: While some checks can be done by homeowners, a qualified electrician or solar technician can perform a more thorough inspection and identify potential problems early on.
• Preventative maintenance: calling out a specialist when its broken is after the fact, a fault that burns down your house would be considered a bit late to call.

Book an inspection.

RenewSolar was established with an objective of redefining existing solar installations to enhance their efficiency and safety. Although the old systems may not have failed, they have been problematic and could pose issues. Therefore, they require cleaning, updating, and thorough inspection. Many companies that performed the initial installations have gone out of business and never followed up, while other companies are reluctant to deal with them.
These systems were not originally designed with the homeowner’s benefit in mind, but we aim to rectify this problem. We offer inspections and testing of your solar setup. as well as upgrades and working with FIT as well as New installations.
Please contact us via phone or email to schedule an appointment and inquire about pricing.