Solar Panel Fuse Size Calculator
Size PV string and array fuses to IEC 62548 (gPV fuses to IEC 60269-6) or NEC 690.8 / 690.9, check the module's maximum series fuse rating, and see whether string fuses are needed at all.
Solar Panel Fuse Size Calculator
IEC 62548: string fuse between 1.5 and 2.4 × Isc. NEC: 1.25 × 1.25 = 1.56 × Isc.
How to Use the Solar Panel Fuse Size Calculator
- 1Pick the standard. IEC 62548 (most countries outside North America) or NEC Article 690 (US).
- 2Enter module Isc at STC. Take it from the datasheet, and enter the number of parallel strings.
- 3Choose string fuse or array fuse. For string fuses, enter the module's maximum series fuse rating to check the upper limit and whether fuses are required.
- 4Read the result. It shows the minimum rating, the maximum permitted rating and the standard fuse that fits between them.
How to Calculate Solar Panel Fuse Size
| Item | IEC 62548 | NEC Article 690 |
|---|---|---|
| String fuse rating | In between 1.5 × Isc and 2.4 × Isc, and not above the module max series fuse rating | In ≥ 1.25 × (1.25 × Isc) = 1.5625 × Isc (690.8(A)(1) and 690.9(B)), next standard size up allowed, and ≤ module max series fuse rating |
| Array / sub-array fuse | In between 1.25 × and 2.4 × the array or sub-array Isc | 1.5625 × sum of parallel Isc |
| When string fuses are needed | When the current from the other parallel strings, (N − 1) × Isc, can exceed the module's reverse-current capability (its max series fuse rating) | Not needed where conductors are rated for the maximum current and the currents from all sources do not exceed the module's max series fuse rating (690.9(A)) |
| Fuse type | gPV to IEC 60269-6 | Listed for PV use (690.9(B)); UL 248-19 PV fuses |
| Voltage rating | ≥ maximum array voltage (Voc corrected for the lowest temperature) | ≥ maximum PV system voltage from 690.7 |
Example 1: Isc 9.8 A, max series fuse 20 A, 3 parallel strings
- IEC: 1.5 × 9.8 = 14.7 A → 15 A gPV. Upper limit min(2.4 × 9.8, 20) = 20 A, so 15 A fits. Reverse current from the other two strings is 2 × 9.8 = 19.6 A, which does not exceed 20 A, so string fuses are not required for module protection.
- NEC: 9.8 × 1.5625 = 15.31 A → 20 A, equal to the module limit, so it is allowed. Fault current from the other strings is 2 × 1.25 × 9.8 = 24.5 A, above 20 A, so string fuses are required.
Example 2: Isc 13.9 A, max series fuse 25 A, 4 parallel strings
- String fuse: IEC 1.5 × 13.9 = 20.85 A → 25 A; NEC 13.9 × 1.5625 = 21.72 A → 25 A. Both are within the 25 A module limit, and fuses are required in both systems (3 × 13.9 = 41.7 A from the other strings).
- Array fuse for the combined 4 × 13.9 = 55.6 A: IEC 1.25 × 55.6 = 69.5 A → 80 A (limit 2.4 × 55.6 = 133.4 A); NEC 55.6 × 1.5625 = 86.88 A → 100 A.
Do You Need String Fuses?
| Parallel strings | Typical answer | Why |
|---|---|---|
| 1 | No | No other string can feed a fault |
| 2 | Usually no | One string can feed at most about Isc (1.25 × Isc under NEC), normally below the module's max series fuse rating |
| 3 or more | Usually yes | Two or more strings can feed (N − 1) × Isc into a faulted string; check against the module rating |
Many string inverters accept one or two strings per MPPT input, so they need no string fuses. Combiner boxes with three or more strings normally need them. Confirm with the inverter manual and module datasheet.
Solar Panel Fuse Size Chart (string fuses)
| Module Isc | IEC minimum (1.5 × Isc) | IEC maximum (2.4 × Isc) | NEC minimum (1.5625 × Isc) |
|---|---|---|---|
| 5.0 A | 7.50 A → 8 A | 12.00 A | 7.81 A → 8 A |
| 8.5 A | 12.75 A → 15 A | 20.40 A | 13.28 A → 15 A |
| 9.8 A | 14.70 A → 15 A | 23.52 A | 15.31 A → 20 A |
| 11.0 A | 16.50 A → 20 A | 26.40 A | 17.19 A → 20 A |
| 13.0 A | 19.50 A → 20 A | 31.20 A | 20.31 A → 25 A |
| 13.9 A | 20.85 A → 25 A | 33.36 A | 21.72 A → 25 A |
| 15.0 A | 22.50 A → 25 A | 36.00 A | 23.44 A → 25 A |
| 18.0 A | 27.00 A → 30 A | 43.20 A | 28.13 A → 30 A |
In every case the fuse must also not exceed the module's maximum series fuse rating. Available ratings depend on the fuse size and voltage; check the manufacturer's range.
Selection Checklist and Common Mistakes
- Use Isc, not Imp. Fuse sizing starts from short-circuit current. For bifacial modules, use the datasheet Isc that includes rear-side gain where the manufacturer gives it.
- DC and PV rated. AC fuses and AC-only breakers cannot interrupt DC arcs reliably. Use gPV (IEC 60269-6) or PV-listed fuses.
- Voltage: 1000 V DC or 1500 V DC to suit the array's cold-weather Voc.
- Upper limit: a fuse above the module's max series fuse rating does not protect the module.
- Cables: string cable ampacity must cover the maximum current and the fault current up to the fuse rating.
Common mistakes: applying the NEC 1.56 factor to an IEC design (or 1.5 to an NEC design); sizing from Imp; picking a rating that exceeds the module limit; using general-purpose gG fuses on PV strings.
Solar Panel Fuse Size FAQ
Under IEC 62548, between 1.5 and 2.4 × Isc and not above the module's maximum series fuse rating. Under NEC, at least 1.56 × Isc (690.8(A) and 690.9(B)), rounded up to the next standard size. For a 9.8 A module that gives 15 A (IEC) or 20 A (NEC).
690.8(A)(1) sets the maximum circuit current at 125% of Isc to allow for irradiance above STC. 690.9(B) then requires the fuse to be at least 125% of that maximum current because PV current is continuous. 1.25 × 1.25 = 1.5625.
Usually not. The healthy string can feed only about its own Isc into a faulted string, which is normally below the module's maximum series fuse rating. Check the datasheet value against Isc (IEC) or 1.25 × Isc (NEC).
A fuse to IEC 60269-6 designed to protect PV strings and arrays. It is DC rated, operates at the low overcurrents that PV modules produce, and is available for 1000 V and 1500 V DC systems.
Add the Isc of all parallel strings. Under IEC 62548, the fuse must be above 1.25 × that total and not above 2.4 × it. Under NEC, use 1.5625 × the total and round up. Select "Array / Sub-array Fuse" in the calculator.
Standards and References
The formulas and reference values on this page follow these standards. For design work, check results against the current edition that applies in your country and the equipment manufacturer's data.
- IEC 62548 – Photovoltaic (PV) arrays: design requirements, including string, sub-array and array overcurrent protection. Published by IEC.
- IEC 60269-6 – Low-voltage fuses: gPV fuse-links for the protection of solar photovoltaic energy systems.
- NFPA 70 (NEC) Article 690 – 690.7 maximum voltage, 690.8(A) maximum circuit current, 690.9(A) and (B) overcurrent protection; 240.6(A) standard ratings. Published by NFPA.
- UL 248-19 – Low-voltage fuses: photovoltaic fuses.
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