Fuse Rating

[Abdul wahid]

Hi. I have a doubt regardng fuse. Imagine that i have a equipmnt which is working at 12v Dc / 3 amps. In this equipmnt power cable have positive (in tis wire having 5amps fuse)and negative terminal. Then i connected the equipment with 12v Dc 30 Amps Power supply. According to fuse behaviour its dependent on current. in this case the supply from power supply is 12 v 30 amp which is passing to through the positive and negative terminal. But how the fuse in positive terminal is still working?according to the fuse behaviour it has to blown. Pls clarify

 

[Martaine2005]

Hi Abdul,
The simplest answer is:
If your equipment requires 3 amps, there will be no problem with the fuse.
The equipment only draws the current it needs. \however, if the equipment develops a fault, the potential for it to draw a massive amount of amps is where the fuse will work (blow).
So only under fault or wrong fuse rating conditions.

Martin

 

[Abdul wahid]

Hi Abdul,
The simplest answer is:
If your equipment requires 3 amps, there will be no problem with the fuse.
The equipment only draws the current it needs. \however, if the equipment develops a fault, the potential for it to draw a massive amount of amps is where the fuse will work (blow).
So only under fault or wrong fuse rating conditions.

Martin

Ty martin. But the thing the power cable to the unit have fuse(positive terminal). It doesnt contain anythg. Imagine one simple wire with fuse hav a fuse rating of 3 amps. If i send 12 v 30 amps into it, i has to blow. Am i ryt?

 

[Martaine2005]

I am not really sure I understand the question sorry.
Is there a fuse? Or just a wire rated at 3 amps?

Also if you send 30 amps? How?
The equipment will 'draw/pull' only the current it requires.

Think of house wiring. The main circuit is 32 amps. But you can still use the same circuit for a 1 amp phone charger with much smaller wire.

Martin.

 

[Abdul wahid]

I will tel u clearly now. I hav one Gps which works at 12v 3amps. This GPS unit having one power cable, which is connected with power supply 12 v 30 amps. power cable(one side connected to the gps unit and other side connected to power supply)
The other side connecred to power supply having two wires: one positive and one negative. In this positive terminal having one fuse 3 amps.

Now my doubt is how the 12v 30 amps from power supply passing through the 3 amps fuse in the power cable

 

[Martaine2005]

Ok, the 12 volt 30 amp supply is just the maximum the supply can deliver if a device requires that amount.
Remember, It's not the supply current rating that is of concern here.
Only the current required by your gps device.
Imagine your device is drawing 1.5 amps from your 30 amp supply, there is still 28.5 amps left for other devices (threoretical example) of course.
Do you understand that example?

Martin