Fire Safety Disconnect Switch for Solar Power Systems
If you’re installing or operating a solar power system, fire safety isn’t an option—it’s a responsibility. In this article, we’ll go over why a solar fire safety disconnect switch is necessary for solar power systems and how the switch itself works. We’ll also examine exactly what kinds of emergency situations this device provides real protection against. This is because solar panels keep the DC side energized during the day even if you turn off the inverter—which is why rapid, safe disconnection is crucial. We’ll specifically discuss why DC-side disconnection is crucial for solar systems and what you need to know about firefighter safety during emergency response. We’ll also help you understand the technical factors to consider when choosing a switch and what determines the price of a solar fire protection switch. Finally, we’ll go over installation considerations for contractors and designers, including what to watch out for when coordinating energy storage and solar fire protection in hybrid systems, and what the most common mistakes are when wiring these switches. The article concludes with a summary and frequently asked questions so you can quickly find the answers that matter to you.
Why is a fire protection disconnect switch necessary for solar power systems?
One of the lesser-known characteristics of solar power systems is that the DC side remains live during the day, even when the inverter is turned off. This poses a serious danger in the event of a fire: the DC cables running inside the building remain potentially high-voltage conductors. The fire isolation switch is designed to mitigate precisely this risk. Hungarian regulations—specifically BM Decree No. 54/2014. (XII. 5.) BM and the related Technical Guidelines for Fire Protection — aims to ensure that, in the event of a fire, the risk of electric shock to building occupants and responding firefighters, as well as the risk of reignition caused by DC arcing in the cables, can be minimized quickly. It is important to note: this is not merely a recommendation—the isolator is a mandatory component in certain installations, such as longer DC circuits running inside a building. How real is this danger? Inside a DC arc, temperatures can reach 3,000–15,000 °C, which can melt the cables and spread the fire to other structures. Therefore, a well-chosen solar panel must always be accompanied by a well-thought-out fire protection solution.
How does a fire protection disconnect switch work?
The logic behind its operation is simple, but the stakes are high. In most solar systems, the DC disconnect switch is built into the inverter; however, after the inverter is turned off, the solar cables running between the solar array and the inverter remain under a DC voltage of up to 1,000 V. The fire-rated disconnect switch solves this problem: it breaks the DC circuit at the point closest to the solar panels, thereby de-energizing the cable section between the switch and the inverter. In many installations, switching off the AC-side fire-rated main switch also triggers the DC-side fire-rated main switch to operate, without requiring separate action. In terms of operating principle, the type that operates on the principle of voltage drop trips immediately in the event of a power outage; the disadvantage is that it must be manually reset—which can be inconvenient for rooftop systems. The operating-current type, on the other hand, trips when a current is detected.
In what situations does the disconnect switch provide protection?
The disconnect switch is not intended for everyday operation, but rather for emergency situations. The most important scenario is a fire: in such cases, it reduces the risk of electric shock to people inside the building and firefighters, as well as the risk of reignition caused by a direct current arc forming on the wires. It also provides protection when firefighters spray water on the burning building, since the de-energized cable section no longer poses an electric shock hazard. This is precisely why regulations require a disconnect switch wherever the outdoor DC run exceeds 10 meters—in such cases, the switch must be located in the immediate vicinity of the solar array. However, it is important to note that disconnection does not solve everything—there may still be wires inside the building that remain energized even after a fire-induced shutdown, and these must be clearly marked.
DC-side disconnection: why is it particularly important for solar panel systems?
Why isn’t it enough to simply turn off the power? Because solar panels cannot be “turned off”: as long as light hits their surface, they generate electricity, and voltage is present at their terminals. In fact, according to the MSZ HD 60364-7-712 standard, the DC side of solar systems must be considered live even when the system is disconnected from the AC grid. The bigger problem is the nature of direct current. An average module produces a DC voltage of a few tens of volts, but when solar cells are connected in series, the string voltage can range from 600 to 1,000 V—regardless of the specific string voltage—while a current of 8–16 A flows; under such a load, an arc as long as 10–20 cm can form. In DC systems, there is no zero-crossing, so the electric arc is harder to extinguish than in alternating current systems. According to statistics, more than half of the fires in solar power plants are caused by DC arcs. This is where the solar fire protection disconnect becomes crucial: conventional inverters do not shut down the DC side simply by disconnecting the AC side, so solar cables can remain under voltages as high as 1,000 V without a fire protection disconnect.
Firefighting Response: What Do You Need to Know About Safety?
For firefighters, a solar power system poses an additional risk, so responding to such incidents requires special preparation. Upon arrival, they must first determine whether the building has a solar power system, and where and how it can be disconnected in the event of a fire. Until this is clear, all DC cables are considered live. Mandatory signage helps with this. A safety sign near the building’s main entrance must warn of the presence of solar panels, and a label or pictogram indicating its purpose must be placed at the disconnect switch—for example, “Solar Panel System Fire DC Disconnect.” Signage must be placed on the cables along the route at intervals of no more than 5 meters so that the situation is clear at a glance. However, fire safety does not end at the switch: cables that remain energized after disconnection must be marked, and the length of those not disconnected by the fire-rated switch must also be indicated. These few signs can save the life of a first responder.
What technical criteria should you use when selecting a disconnect switch?
It matters which switch you install in the system. The first consideration is the DC rated voltage and current: devices on the market are typically rated for up to 1,000–1,500 V DC and 38–40 A, and are available in sizes designed for different numbers of strings. You must match these to the parameters of your strings. Although inverters compliant with MSZ EN 62116 automatically disconnect from the AC grid, this does not de-energize the DC side—therefore, the disconnect switch must be selected separately from an electrical standpoint. The operating principle is also important. The motorized, automatic type disconnects without human intervention and does not require special wiring; the live-current version, on the other hand, requires fire-resistant wiring and operating voltage, which increases installation costs. Pay attention to galvanic isolation: optimizers consisting exclusively of semiconductor components cannot be used as fire-rated circuit breakers. For outdoor installation, IP65/IP66 protection and UV resistance are required, and certification must comply with EN 60947-3 / CE / TÜV. Selecting the appropriate fire protection switch is therefore always a system-level decision.
What determines the price of a solar panel fire protection switch?
There is no standard price, as the cost of a solar panel fire protection switch is determined by several factors. The biggest factor is the operating principle: the voltage-drop type is the cheapest, the motorized automatic solution is more expensive, and the operating-current type is the most costly due to the fire-resistant wiring. The price is also driven up by the number of strings managed, built-in MC4 connectors, and remote control or app-based monitoring. As a rough guide: even a single-string switch with manual reset starts at around 70,000–120,000 forints plus VAT, while premium market products can be significantly more expensive. The right choice here isn’t the cheapest option, but rather the device that best suits the system.
Installation Considerations for Contractors and Designers
Contractors and designers share a common responsibility here: ensuring the operational readiness of fire-protection circuits is not only the task of the electrical designer and contractor, but also of the architect and the fire protection designer. The most important factor is the location of the switch. If the disconnect switch is placed next to the inverter, deep within the building, then in the event of a fire, the entire internal DC cabling will remain live—which no longer complies with fire safety principles. The correct placement must always be adapted to the building structure and the DC cable route, not to the inverter. For longer outdoor cable runs, the switch is thus placed next to the solar panels, near the support structure. Two basic rules: AC switches cannot be used on the DC side, and adequate IP protection is required outdoors. In a pre-assembled DC box, the manufacturer has already coordinated the fuses, surge protection, and disconnect switch, which reduces the likelihood of errors.
Energy Storage and Solar Panel Fire Safety: What to Watch Out for in Hybrid Systems?
A hybrid system consists of solar panels and an energy storage unit (battery), which introduces new fire safety risks. In practice, it is advisable to design the energy storage unit and the hybrid inverter within the same fire compartment, as this simplifies isolation and labeling. In installations with energy storage, DC isolation is required on the cable run between the hybrid inverter and the energy storage system if they are not located in the same fire compartment or if the length of the run exceeds 5 meters. Fire protection for energy storage systems also requires special labeling: it must be indicated that the active conductors may remain energized even after disconnection. Furthermore, separate fire spread recommendations apply to larger Li-ion storage systems exceeding 5 kWh.
Common Mistakes When Wiring Switches
Certain errors recur time and again during installation. The most common mistake is placing the disconnect switch next to the inverter, deep within the building—as a result, the internal DC circuit remains energized throughout, and the solution fails to comply with fire safety principles. Another typical mistake is connecting an AC switch to the DC side, even though it cannot open without arcing, or attempting to use an optimizer consisting of semiconductor components as a fire-case disconnect switch. With the operating current switch, it is also a mistake to omit the fire-resistant cable and the operating voltage. It is also common to omit labeling wires that remain live. Another source of errors is improper grounding—poor grounding can lead to arcing and fire. Careful planning of the solar panel grounding system helps prevent this.
Frequently Asked Questions (FAQ)
Is a fire protection disconnect switch required for every solar system?
Not always. It is required if the outdoor DC run to the entry point is longer than 10 meters, the indoor section to the inverter exceeds 5 meters, or the DC cable passes through one or more floors. Even in other cases, it is worth installing one to protect lives and property.
Does a fire protection switch prevent fires?
No. It does not protect against fire on its own; its purpose is to de-energize the DC side in the event of a fire, thereby reducing the risk of electric shock to occupants and firefighters.
Can the fire isolation switch be retrofitted?
Yes, it can be installed in an existing system, but the switch must be located as close as possible to the solar panels, or at the very least at the building’s entry point—and be sure to have the work done by a professional.
How much does a fire protection disconnect switch cost?
A single-string, manually reset solution starts at around 70,000–120,000 forints plus VAT, while motorized, multi-string, and remote-controlled devices are typically more expensive.
Who can install the fire protection circuit breaker?
An electrician, since this involves electrical work; and if the building’s fire safety classification changes, the project can begin once the construction plan is approved. Therefore, leave it to a qualified contractor.
