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One of our fuses in our secondary fuse box just blew. Luckily, there there is a backup. I am not an electrical professional but I know a little 101.

I just want to ask about the correct fuse / amps to install if I have this kind of setup:

enter image description here

As I said, one of the small fuses just blew and I replaced it with a 30 A fuse. Is it safe to use 30 amps? Because when both of my aircon and computer is on, the fuse copper was sparking. I am not sure what's causing it - is it the contact between the fuse holder and the fuse, or is it the fuse itself that just can't handle the current flowing? I noted when I turned off my PC, I don't see any spark.

Anyway the fuse I was using is this:

enter image description here

I am using 30amps, I think those are the big ones installed in our main fuse box.

Can you please give some advice about proper installation and what type of fuse to use?

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    \$\begingroup\$ You should always replace a fuse with one of the same or lower amperage, never higher. \$\endgroup\$ – stevenvh Jun 23 '12 at 15:18
  • \$\begingroup\$ @stevenvh I ran and took a quick look on our secondary fuse box and all of them has 30amp fuse. What could be the cause of the sparks? I just thought maybe it was the contact but maybe you guys can see something else \$\endgroup\$ – Jayson Ragasa Jun 23 '12 at 15:22
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    \$\begingroup\$ A spark means a bad contact. But I'm not acquainted with that type of fuse, or how they're mounted, so I'm hesitating to give you advice; this is about your safety. (In Belgium we use this type of automatic fuse.) \$\endgroup\$ – stevenvh Jun 23 '12 at 15:31
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    \$\begingroup\$ @JaysonRagasa - I think Steven has a point here - you probably have no answers as people (me included) will be reluctant to risk giving 100% good and correct advice. Even with the right advice, it risks being misinterpreted, so I think it's probably best for you to get a local electrician in, preferably to fit you a fuse made during this century ;-) \$\endgroup\$ – Oli Glaser Jun 24 '12 at 1:06
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    \$\begingroup\$ Please speak to an electrician soon - poor contacts in high current wiring are a major cause of electrical fires. The sparking causes the contact to get worse, causing more heat and sparking and so on. \$\endgroup\$ – Cybergibbons Jan 20 '13 at 12:52
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The type and rating of the fuse you must use depends on your local regulations and laws, so it is difficult to help without knowing.

However, the regulations, no matter in which country, depend on physics - more precisely, they ask if the fuse will prevent the wires, switches and outlets from burning in case something fails and causes an overcurrent.

Despite your nice diagram, we can't tell what types (diameters/cross section) of wire are used in your installation, and where the wires are put. For example, different ratings apply depending on whether your wires are laid out in a stone wall or in a wooden construction, or in a wooden construction containing some thermal insulation making it harder for your wires to get rid of heat.

A typical installation in Europe, for example uses wires with a cross section of 1.5 mm2 and fuses with 16 A. If the cross section of the wires is smaller, the fuses have a lower rating, too. If the wires are put inside of thermal insulation material (e.g. in an outside wall or along the roof), you may have to use 13 A or even 10 A for the same 1.5 mm2 wire.

If you are not absolutely certain about your local regulations, please ask a professional electrician. If not done right, you put your house in danger of burning down.

Also, if you have sparks in your fuse holders, I think it's time to replace the entire fuse-and-holder combination. Sparks / arcing may cause very much heat, starting a fire in your fuse compartment!

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    \$\begingroup\$ I'll one-up that. Nothing to do with local regulations-- there's something wrong and an electrician should be called in. \$\endgroup\$ – Scott Seidman Mar 21 '13 at 20:37

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