Fuses are grouped by the voltage they protect and by what they protect. High-voltage and low-voltage fuses differ not just in rating but in how the arc is contained and interrupted. Understanding the structure behind each type helps you specify the right insulating tube, because the same fault that a 400 V panel fuse shrugs off will destroy a tube that was never built for medium voltage.
The dividing line
The usual dividing line is 1 kV. Low-voltage fuses protect systems at or below 1 kV, which covers residential panels, industrial control gear, motors, and appliances. High-voltage fuses, more precisely medium-voltage in most distribution work, protect systems above 1 kV, such as transformers, capacitor banks, and outdoor switchgear. The line is a convention, not a physical cliff, but it tracks a real change in arc behavior: above roughly 1 kV the arc carries enough energy that the fuse must actively force it to extinguish rather than simply let it stretch and cool.
By voltage and protection object
By voltage, fuses split into high-voltage and low-voltage types. By what they protect, they cover transformers and general equipment, voltage transformers, power capacitors, semiconductor devices, electric motors, and household appliances. The protection object matters because each load has a different inrush and overload profile, and the fuse curve has to sit above that profile while still clearing a fault.
By structure
Open fuse. The element is exposed to air on porcelain supports, with no enclosure. Simple and suited to low-voltage outdoor use, but it makes a loud arc flash when it clears.
Semi-enclosed fuse. The element sits in a porcelain frame with metal sockets at both ends, for low-voltage indoor use. The frame contains the flash.
Tube fuse. The element is sealed inside an insulated tube with metal caps or contact blades at both ends. Fill the tube with quartz sand and it gains a current-limiting effect and much higher breaking capacity, which is why it is also called a high-breaking-capacity fuse. Evacuate the tube and it is a vacuum fuse; fill it with SF6 and it is an SF6 fuse. Quartz, vacuum, and SF6 all give strong insulation, so these tubes suit both low- and high-voltage use.
Spray (jet) fuse. The element is mounted in a tube made of solid gas-evolving material such as electrical pressboard or acrylic. On a short circuit the element melts, the arc heats the wall, and the material releases high-pressure gas that drives the ionized gas out both ends, extinguishing the arc at the AC zero crossing. Drop-out cutouts on distribution lines are the classic example.
How the two classes interrupt
The structural difference shows up most clearly in the interrupting medium. A low-voltage fuse often relies on air and a filler, with a modest arc voltage and a short arc path. A high-voltage fuse has to build a much higher arc voltage so the arc cannot restrike after the current zero. Filled quartz and gas-evolving walls do that work: they cool the arc, raise its resistance, and split one arc into many series arcs. This is why the tube material matters far more at medium voltage than at low voltage, and why you cannot judge a tube on dimensions alone.
High voltage vs low voltage at a glance
- Typical range. Low voltage up to 1 kV; high voltage above 1 kV, commonly 3.6 kV to 40.5 kV in distribution.
- Arc control. Low voltage stretches and cools the arc; high voltage actively forces extinction with fill or gas evolution.
- Tube material. Low voltage often uses simple ceramic or molded bodies; high voltage uses melamine laminate, vulcanized fiber, or filament-wound composite.
- Breaking capacity. Low voltage clears modest fault levels; high voltage must clear tens of kiloamps with a controlled let-through.
- Service. Low-voltage fuses are usually replaced like a cartridge; medium-voltage cutout tubes may be single-operation by design.
By breaking-current range
General-purpose fuse. Clears from about 1.6 to 2 times rated current up to maximum breaking capacity. Used for power transformers and general equipment.
Backup fuse. Clears from about 4 to 7 times rated current up to maximum. Often paired with a contactor, which handles the lower overload range; used mainly to protect motors.
Full-range fuse. Covers the whole range from low overload to maximum breaking capacity.
Special types also exist for specific needs: electronic fuses, thermal fuses, and self-resetting fuses.
What this means for the insulating tube
For tube and spray fuses, the wall material decides arc containment and dielectric strength. Melamine tubes give stable insulation and good arc resistance for filled and high-breaking-capacity designs, while vulcanized-fiber and composite tubes serve other structures. We produce these tubes under ISO 9001 and provide SGS material testing.
Frequently asked questions
Which tube material should I choose for a filled HV fuse?
For quartz-filled, high-breaking-capacity fuses, a dimensionally stable, arc-resistant tube such as melamine laminate is a common choice. Send your design and we will recommend a material and tolerance.
Can a low-voltage fuse be used above 1 kV?
No. Voltage rating is a limit on the fuse’s ability to extinguish the arc, not a label. Using a fuse above its rated voltage risks failure to clear the fault and possible rupture. Always select a fuse rated at or above the system voltage.
Do you supply custom tube sizes?
Yes. We customize ID, OD, wall thickness, and length to drawing, with low minimum order quantities for development.
Specifying tubes for a new fuse design? Email sale@fusestube.com for samples and material data, or see our fuse tube products.
