Product Overview
3A 250V Glass Cartridge Fuse in the Standard 5mm x 20mm Metric Size
Condition
New, unused stock, sold one piece at a time. The photographs show a single sample from the bin: a clear glass tube with nickel-plated end caps, one straight fuse element wire intact and centered inside the glass, and no darkening, soot, or clouding on the inside of the tube. Small stamped markings are present on the end caps but are not fully legible in these photos, so treat the ratings here as they are listed rather than as a caption read off the metal. Those stamped marks are not legible enough to identify a maker, so it is listed here as unbranded. The plating carries a little mottling from loose storage. Held in the caliper, the body measures approximately 20 mm end to end, which matches the 5mm x 20mm metric size the fuse is sold as.
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Product Overview
This is the small glass cartridge fuse that lives in nearly every piece of imported bench gear, test equipment, power supply, and appliance built to metric practice: 5 mm diameter, 20 mm long, rated 3A at 250V, listed here as the 51NM. The construction is the classic one, a clear glass barrel capped at both ends with plated ferrules and a single fuse wire bridging them, so you can hold it to the light and see whether the element is intact before you ever reach for a meter. Clear glass is the reason this style has outlived fancier packages on service benches. The 250V figure is the maximum voltage the fuse is built to interrupt, so it suits ordinary 120V and 240V equipment as well as low-voltage rails, provided the 3A current rating is what the equipment calls for. Blow characteristic - fast-acting versus time-delay - is not confirmed here; check what your equipment specifies before fitting one.
Key Features
- Current rating: 3A
- Voltage rating: 250V
- Size: 5mm x 20mm metric cartridge, approximately 20 mm long against the caliper
- Body: clear glass tube with plated metal end caps
- Element: single straight fuse wire, visible and intact in the photographed piece
- Listed part reference: 51NM
- Brand: unbranded - the stamped end-cap marks are not legible enough to identify a maker
- Condition: New, sold each
- Blow characteristic (fast-acting or time-delay): not confirmed - verify against your equipment's requirement before use
Applications
- Bench technician restoring a European or Japanese instrument that takes a 5 x 20 mm fuse in a panel-mount holder
- Repair shop restocking the drawer with common 3A values instead of ordering a full box for one job
- Audio hobbyist replacing the mains fuse in an amplifier chassis after chasing down the real fault
- Maintenance electrician keeping a few spares in the toolbag for machine control panels that use metric fuse holders
Frequently Asked Questions
Will this fit a standard 5 x 20 mm fuse holder?
Yes. This is the standard metric cartridge size used by panel holders, inline holders, and PCB clips built for 5 x 20 mm fuses. In the photos the sample sits in the caliper at roughly 20 mm end to end.
Is it fast-acting or slow-blow?
Not confirmed. The end-cap stamping is not legible enough in these photos to read a blow-characteristic code, and we do not guess at markings. If your equipment specifies a time-delay fuse, confirm that before fitting one of these.
Can I use a 250V fuse in a 120V circuit?
The voltage figure on a fuse is a maximum interrupting rating, not an operating requirement, so a 250V fuse is normally acceptable at or below that voltage. The number that must match your equipment is the 3A current rating. Follow the equipment maker's fuse specification, which is usually printed beside the holder.
How can I tell the fuse is good before I install it?
With glass fuses you can look. The element wire runs straight between the caps in the photographed piece with nothing scorched or broken. A continuity check on your meter takes a second and settles it either way.
Why buy three or four here instead of a box of 100 somewhere else?
Because almost nobody needs 100 fuses. This one is sold each, so you take the two for the repair and the two for the drawer and stop there. Shipping is $8 flat rate and free once the order passes $28, which is easy to reach if you are picking up other small parts in the same visit, and orders leave our Idaho warehouse the same or next business day.
A fuse is the one part you buy hoping it never gets to do its job. Slide a couple of these into the drawer and the next time something upstream gets excited, the cheapest piece in the chassis is the one that gives way.
