Why the main knife fuse always burn out?

My installation circuit is concealed. Wire is installed on the wall, and recently main knife fuse always burn out, then good and bad. Should not be to overload, do you know the reason, and how to solve?

If you know it is not overload. then the only other solution is bad insulation of the wires.
This can be tested by use of a high voltage insulation tester 500V. there your leak current is measured.

You can do some kind of analysis in terms of how long does it take to blow the fuse. Does it blow instantly or does it blow after minutes or an hour ? What is the rated current of the fuse ? Then you could go into the data sheet and estimate the current flowing when the fuse blows. Did you calculate the expected current in your circuit ? Maybe everything is ok, but the fuse is to small ? Did it work before ? Was something changed in the circuit ? Maybe you have more information for us ?

A fuse will only open when its current rating is exceeded. Your circuit is drawing more current than the fuse is rated for. It is overloaded.

As far My experience in this situation, insulation level is very weak, if these is any joint in the cable than may be joint fails which in result make direct contact between line to line , line to neutral and line to ground fault cause of knife type fuse burning in feeder pillar.

Do you know how to change the fuse ***safely*** ?
Is this in an ordinary house ?
Do the lights and the power sockets all go dead, or do some things still work ?
Did the fuse blowing start after a new item of equipment was installed ?
Do you know how to calculate how much current all your electrical appliances take ?

I will check out the wires.

I think it is not overload.

Overload you can calculate easy
Voltage X Fuse rating = Maximum line load in Watt / VA.
so 230 V. X 16Amp. = 3620 Watt so it is best not to load more than 3000Watt.

Also keep in mind if the original fuse was a slow blow do not replace for fast blow, if there is a equipment connected that have big start up current, like a big air condition or compressor.

If the isolation is bad from the wires you can also smell a burn smell and it is asking for a electrical fire. All wires need to be replaced and the system not powered until then.