Guides · TOSUNLUX
How to protect a photovoltaic installation on the direct current side?
Between the panels and the inverter, the current is direct: it never passes through zero, the electric arc does not go out by itself, and devices must be designed for direct current. The TOSUNLUX (Tosun) solar range covers the whole protection chain on the DC side, up to 1,000 V DC.
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The short answer
- One gPV fuse per string when several strings are in parallel: TSPV-25 in a TSPV-25B fuse holder.
- A DC switch-disconnector before the inverter: S32D-TL, lockable.
- A DC surge protective device: TSP7-40 1,000 V DC.
- DC breakers for battery and control circuits: TSB5-63DC or TSM3-320DC.
- Properly crimped MC4 connectors, and a weatherproof enclosure outdoors.
Why direct current needs specific equipment
A device designed for alternating current may not break an arc in direct current. Every device on the DC side must therefore state a DC operating voltage at least equal to the maximum voltage of the panel string (open-circuit voltage in cold weather), and a suitable utilisation category. The calculation is based on the module and inverter data sheets; your installer or design office does it.
The DC protection chain
| Function | TOSUNLUX series | Characteristics (FAPELEC catalogue) |
|---|---|---|
| String protection | TSPV-25 gPV fuses + TSPV-25B fuse holder | 10 × 38, 15 · 20 · 32 A, 1,000 V DC, breaking capacity 30 kA |
| Isolation before the inverter | S32D-TL disconnector | 32 A, up to 1,200 V DC, DC-PV2, arc time < 8 ms, lockable |
| Modular DC protection | TSB5-63DC / 125DC breakers | 10 to 125 A, 2P 500 V · 3P 750 V · 4P 1,000 V DC, 6 kA |
| High currents, batteries | TSM3-320DC moulded-case breaker | 2P, 100 · 160 · 200 A, 1,000 V DC, 20 kA at 1,000 V |
| Surges (lightning) | TSP7-40 DC surge protective device | Type 2, 1,000 V DC, Imax 40 kA, In 20 kA |
| Cable connection | MC4 connectors | 30 A, 1,500 V DC (IEC), IP67 when mated, 2.5 · 4 · 6 mm² cables |
String fuses: when and how
When several strings are connected in parallel, a faulty string can receive current from the others. One gPV fuse per string protects it. Its rating is determined from the short-circuit current of the modules and the reverse current they withstand, according to IEC 60364-7-712; the design office does the calculation. TSPV-25 cartridges fit the 18 mm modular TSPV-25B holder, on a DIN rail.
For a small installation with one or two strings, the MC4-1F connector with a built-in fuse is another option.
The disconnector before the inverter
The S32D-TL isolates the panels from the inverter for maintenance. It suits residential and commercial installations from 1 to 20 kW, switches under load (category DC-PV2) and locks in the OFF position: nobody can close it again during work. Its polarity does not matter.
Batteries and hybrid inverters
Between batteries and inverter, currents are high. The TSM3-320DC (100, 160 or 200 A, 1,000 V DC) protects these links with a high breaking capacity and also isolates them. For smaller circuits, modular TSB5-63DC breakers mount on a DIN rail.
Outdoors: weatherproofing
HT and HB IP65 enclosures, in UV-resistant plastic, house fuses, disconnector and surge protection near the panels. MC4 connectors are IP67 when mated, but only IP2X when unmated: do not leave them open in the rain. On the AC side of the inverter, see the guide surge protective device type 1 or type 2.
Frequently asked questions
Can an AC circuit breaker be used on the solar panel side?
No. The DC side requires devices designed for direct current, with a DC operating voltage at least equal to the maximum string voltage, such as the TSB5-63DC (up to 1,000 V DC in 4 poles).
Is one fuse per string needed?
When several strings are in parallel, generally yes: one TSPV-25 gPV fuse per string, rated by the design office according to IEC 60364-7-712.
Which disconnector between the panels and the inverter?
The S32D-TL: 32 A, up to 1,200 V DC, category DC-PV2, lockable in the OFF position.
Are MC4 connectors waterproof?
IP67 when mated, IP2X when unmated. They take 2.5, 4 and 6 mm² cables and 30 A.
TOSUNLUX series mentioned
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