How do I start selecting a Bussmann fuse?

First decide the duty: protect a semiconductor, a DC string or a branch circuit. Then fix the voltage class from the circuit, set the amp rating from the load, choose the class and body from the holder and the space, and confirm the interrupting rating. Those decisions narrow the range quickly.

High-speed, solar or branch fuse: how do I choose?

Choose a high-speed fuse to protect a power semiconductor in a drive or rectifier, a photovoltaic fuse for a DC solar string, and a branch circuit fuse for panel, feeder and motor protection. The duty determines the class and the coordination rules. The duty, not the amp rating, is the first decision.

How do I check coordination?

Compare the fuse clearing I-squared-t with the device withstand I-squared-t at the prospective fault current and confirm the fuse clears first. For branch circuits, compare the time-current curves so the correct fuse operates first. Our FAE team can run the coordination check.

What selection mistakes should I avoid?

The usual mistakes are ignoring the interrupting rating, using an AC fuse in a DC circuit, and forgetting the ambient derating. Each adds risk without benefit, and in a fault the fuse may not clear at all. Validate the choice against the single-line diagram before ordering.

How do I coordinate a high-speed fuse with a semiconductor?

Compare the fuse clearing I-squared-t with the device withstand I-squared-t at the same prospective fault current and confirm the fuse clears first across the whole fault range, then check the voltage class and the amp rating. Coordination is what makes the fuse protect the device.

Why does current limitation matter?

A current-limiting fuse opens so fast that the fault current is cut off before it reaches its first peak, so the device sees much less energy than the prospective current would suggest. That let-through energy is what the fuse I-squared-t describes. It is why a high-speed fuse protects a diode that a breaker cannot.

How should I mount a square-body fuse?

Bolt the square-body fuse directly to the busbar with the correct torque, so the connection has the lowest practical inductance and the fuse cools through the bar. A loose connection adds resistance and heat and can cause a nuisance failure. Our FAE team can review the layout.

Does the environment affect the fuse rating?

Yes. A fuse in a hot enclosure carries less current, so the amp rating must be derated for the ambient and the mounting. In a high-power stack, also check the fuse and the holder together, because the holder can be the limiting part. Request a derating check for your panel.

How do I size a PV string fuse?

Start from the array short-circuit current, apply the correction factors in the module datasheet and the fuse standard, then confirm the fuse carries the string current at the hot ambient of the site. Keep the rating above the normal current and below the cable and module rating. Our FAE team can run the derating calculation.

Why is derating so important in solar?

A solar installation runs hot, and a fuse carries less current as the ambient rises. If the fuse is sized only at 25 degrees Celsius it may nuisance-open on a hot afternoon; if it is oversized to avoid that, the cable may be under-protected. The ambient correction is the key step. Use the site maximum temperature, not the average.

Which holder should I use?

Use the matched Bussmann holder for the fuse family, such as the CHPV finger-safe holder for 10 by 38 mm links and the SD blade blocks for the NH links. The holder must be rated for the DC voltage of the array, not just the fuse. Choose the fuse and holder as a pair.

Can I use an AC fuse in a PV system?

No. A photovoltaic array produces a DC fault current with no natural zero crossing, so an AC fuse cannot be relied on to clear it. Only a DC-rated PV fuse, carrying the gPV class, is safe in a solar string or combiner. This is the single most important rule in PV protection.

My fuse opens on every motor start. Where do I start?

Check whether the fuse has time delay for the motor inrush. A fast-acting fuse on a motor branch will open on a normal start, so the fix is usually a time-delay part such as a Low-Peak Class J or Class CC fuse of the correct rating. Measure the inrush and compare it with the fuse curve.

Why does the whole panel go out on one fault?

That is a selectivity problem. Compare the time-current curves of the branch and upstream fuses and confirm the branch fuse is faster across the whole fault range, including the overload region where curves can cross. Re-rate one of the fuses so the branch clears first. Our FAE team can run a selectivity check.

The fuse holder is running hot. Why?

A hot holder usually means a loose connection, an oxidised contact or a holder rated below the fuse current. Check the tightening torque, clean the contacts and confirm the holder and fuse ratings match, then re-measure the temperature under full load. Do not simply fit a larger fuse.

A high-speed fuse blew. Is the device safe?

Usually yes: a high-speed fuse that clears a fault protects the device it was coordinated with. Examine the fuse for the arc mark that shows it cleared a real fault, find the fault before replacing the fuse, and re-check the coordination before returning the unit to service. Request a coordination review before restart.

Technical Support | Bussmann Expertise | BeiLuo

Guides, application notes and troubleshooting from BeiLuo's FAE team covering Bussmann high-speed, solar and branch circuit fuses and their matched holders.

Guides 1 Application Notes 2 Troubleshooting 1 Reviews 0

How to Select a Bussmann Fuse: A Practical Guide

2026-07-24 - Guides - By Wu Gang

Compare Bussmann high-speed, solar and branch circuit fuses by class, voltage, amp rating and I2t to choose the right fuse for your circuit and application.

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Bussmann High-Speed Fuse Application Notes

2026-07-17 - Application Notes - By Wu Gang

Coordination, I2t and layout guidance for Bussmann high-speed fuses that protect power semiconductors in drives, rectifiers, inverters and other converters.

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Bussmann Solar PV Fuse Application Notes

2026-07-10 - Application Notes - By He Qian

String-current, ambient derating and holder selection guidance for Bussmann photovoltaic fuses in solar combiners, inverters and storage systems of all sizes.

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Bussmann Fuse Troubleshooting and Selection Review

2026-07-03 - Troubleshooting - By Deng Bo

Diagnosing nuisance fuse opening, poor coordination, holder heating and selective-trip problems in Bussmann fuse installations, with practical fixes for each.

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Meet Our FAE Team

Wu Gang

Senior FAE Engineer, Circuit Protection

FusesCoordinationHigh-Speed

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He Qian

FAE Engineer, Solar Protection

Solar PVDC ProtectionDerating

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Deng Bo

FAE Engineer, High-Speed Fuses

Semiconductor FuseI2tCoordination

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