ST-Glass Fuse

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Glass Fuses for Voltage converters and step down transformers. Anti-surge cartridge fuse.

8ZED Anti-surge cartridge glass fuses for voltage converters and step down transformers.

If you need a replacement fuse you will need the correct  fuse size and style, below is the reference chart.

US Models Japanese Models
FUSE RATING         
STXP-U100 500Ma M205  STXP-J100  500Ma M205
STXP-U200 1 Amp M205  STXP-J200  1 Amp M205
STXP-U500 2.5A M205  STXP-J500  2.5A M205
STXP-U1000 5A 3AG  STXP-J1000  5A 3AG
STXP-U1500 8A 3AG  STXP-J1500  8A 3AG
STXP-U2000 10A 3AG  STXP-J2000  10A 3AG
STXP-U3000 15A 3AG  STXP-J3000  15A 3AG
STXP-U4000 20A 3AG  STXP-J4000  20A 3AG
STXP-U4000 25A 3AG    



  1. Make sure you have turned off the power at the 240v power point
  2. Untwist the fuse Holder anti-clockwise until the cap comes off.
  3. The fuse "pops out" (glass cylinder)
  4. The filament inside may be broken (some are difficult to see as they may break at the end)
  5. Place a new fuse into the cup part holder
  6. Twist the fuse holder clockwise until its screwed all the way in
  7. Turn the power on at the 240v power point You should hear a “Boing” spring sound as the transformer energizes 

Criteria Fuse Selection

Circuit overcurrent protection is important. Inadequate selection of fuses can lead to the breakdown of equipment, resulting in replacement costs.

The function of a fuse is to interrupt an uncontrolled fault current or overcurrent before serious damage can occur, such as the overheating of equipment.

Because a fuse is designed using a fusing element, it is particularly suited for reliable interruption of short-circuits. With overcurrents up to 2x or 3x the rated current, a fuse becomes less accurate and, as such, not so well suited for these conditions. Other overcurrent protection measures such as electronic protection, thermal overload elements or additional fuses are then necessary.

Normal Operation
After Switching ON under normal operating conditions, a fuse is subjected to a maximum operating current and a maximum operating temperature. A derating of the rated current is therefore usually necessary since a fuse is rarely operated at the set ambient temperature of 23 ˚C. As an example, let’s look at a scenario using a time-lag SMD fuse such as the UMT 250 from SCHURTER. With an operating temperature of 60 ˚C, the fuse needs to be derated by 17%, i.e., when the operating current is 1 A @ 60 ˚C, a rounded-up fuse value of 1.25A (1A / 0.83) is necessary.

Fuses can be in accordance with IEC 60127 or UL 248-14. Because of the different definitions between the two standards, fuses are not directly interchangeable as follows: fuses in accordance with IEC 60127 may be operated continually at 100% of the rated current value, whereas fuses in accordance with UL 248-14 only at 75%. UL 248-14 specifies a minimum of 4h operating time at rated current.

The self-heating effect of time-lag fuses is less than that of quick-acting. This can be seen from the typical values of voltage drop. For example, a 2 A 5x20 mm glass time-lag fuse has a typical voltage drop of 60 mV, whereas a typical quick-acting version is 90 mV. This difference is evident by the thicker fuse element (higher melting value I2t, see point 2) that is necessary for time-lag fuses. It should also be noted that fuses are heated by the current until element melts (opens) and interrupts the circuit.

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