IDM - Where to install fuses and fuse terminal blocks?

The fuses are apparatus of protection that should include in IDM/SDM installation. To define de right local to install, you should consider some points listed below:

• PT used;
• Values of the fuse;

The use of these devices is indicated and necessary because, in the event of a shot circuit, there is no appreciable damage to the monitoring IED.

Product Specifications:

Is possible to access more detailed specifications of the pieces of equipment IDM and SDM above:

IDM:

TP:

Choose the appropriate local to install:

The fuses can be used before or after the PT of the commutator motor voltage measurement. It will depend on the criteria of each project.

In the topics below, some advantages and disadvantages of each kind of installation will be shown:

Fuse terminals installed on the primary PT measurement:

Fuse terminals installed on the secondary PT measurement:

Fuses specifications:

For the applications using the measurement PT, supplied by Treetech, we highly recommend the following specifications:

• Installing on the PT primary:
  • Fuse terminals SHT-4H Phoenix;
  • Glass fuse 5x20 mm, 50 mA, commutator motor voltage, class F.
• Installing on the PT secondary:
  • Fuse terminals SHT-4H Phoenix;
  • Glass fuse 5x20 mm, 100 mA, 250 V, class F.

Further guidance:

1. IDM inputs use, at most, mA units. In other words, the smaller the fuse, the more protected it is.
2. The recommendation for using 100mA is that, at a given current, it will burn out very quickly. But it is not just any fuse that you can use. It is possible to check the spreadsheet at the bottom of this page for the actuation time.
3. The glass fuse of 100 mA, class F, is one of the lowest electrical currents and it is still easy to find.
4. Is possible to use a 150 or 200 mA? Yes, it is an option, but it can burn out very slowly. The longer it takes to burn out, the more the protected product has to endure. You can see the comparative table of actuation times in the enclosed data sheet.
5. Important hint: Have low filament strength. The lower the better. This item is usually not in the documentation and varies with each manufacturer. The best quality ones have R<10 ohms. Resistances higher than 10 ohms cannot be used in current inputs, as they disturb CT measurements.

Fuse test mode:

Using a multimeter in ohms, low impedance:

• If there is continuity or very low resistance (less than 10 ohms) the fuse is in good condition.
• If there is no continuity or infinite resistance, then the fuse is open (blown). Replace it with one of the same currents.
• Intermediate states, in other words, high resistances, may indicate the presence of moisture, but in any case, the fuse is open and must be replaced.

Of course, fuses with transparent glass casings can easily be checked visually. If the internal wire is interrupted, it is certainly open or blown. What happens is that sometimes the fuse has the internal wire interrupted near the soldering point, at one end, and this cannot be observed, giving the impression that it is good when it is not. If in doubt, test it! (How to test fuses (INS042)).

Additional Information:

• Glass Fuse (Fast Action) 5x20mm (Pack of 10 Pieces) - ZH - Eletrolico - Industrial Automation 24h!  
• Fusi - Bras. Fusíveis Brasileiros Ltda
• Attached are the datasheets of the fuse and the fuse terminal block.