Where do you connect the fuse cable wire from a car stereo you have a Red wire that is the live a black wire that is earth and a yellow wire that is for fuse where do you connect the yellow wire too?

Some people may want to use a bunch of smaller, individually insulated, wires (like ten 14g wires) in place of one larger wire (like a 4g wire). This may be OK as far as current carrying capacity is concerned but the problem comes in when you have to fuse it. A 4g wire can handle about 125 amps.

A 14g wire can handle about 15 amps. If one of the strands of the 14g wire is shorted to ground (like where it runs through the firewall), the main 125 amp fuse would not blow and the wire would burn. To properly protect the multiple strands of insulated wire, you'd have to use ten 15 amp fuses in individual holders (each wire would have its own fuse).

I know that this may be an 'off the wall' situation but I've had several emails about this (generally concerning two or three 8g wires and a large wafer fuse) so there are, at least, a few people who don't fully understand this. These are the recommended maximum fuse ratings for the corresponding wire size. Using a smaller fuse than what's recommended here will be perfectly safe.

A fuse does not blow when the current reaches its rated current. It is designed to pass its rated current without opening. A fuse will take varying times to blow under different conditions.

A fuse will pass significantly more than its rated current for a very short time. It may take 10 minutes or more to blow a fuse at 25% over its rated current. The table below is an example of the specifications for a slow blow fuse.

You can see that a 20 amp fuse may pass 40 amps of current for as long as 5 minutes before blowing although it probably wouldn't take a full 5 minutes to blow. The times for other fuses will be slightly different. This graph lets you see the estimated time that it might take for an ANL type fuse to open.

The data used to create the graph was found on the Bussmann web site. You can see that it would take as much as 10 seconds to blow at double its rated current flow but it would only take approximately 0.1 seconds to blow it if 1000 amps of current passed through the 100 amp fuse. If your amplifiers would intermittently draw 200 amps, the fuse probably would not blow.

If they drew 200 amps for more than 10 seconds, the fuse would likely blow. If the wire was shorted to ground, the current flow would be extremely high (probably more than 1000 amps) and the fuse would blow almost instantly. Although it's obvious when a fuse has blown/opened as it is designed to do but a lot of people still want to know what a blown fuse looks like.

Below are several examples. The first image has three 15 amp fuses. The one on the left is a normal fuse.

The fusible element is intact. The middle fuse blew from a slight overload. The fuse on the right has blown violently.

When the element essentially explodes splattering the entire window with the molten remains of the fusible element, you know it was a significant overload. In this image, you see what it looks like when a glass fuse blows as it was designed. Again, this was a significant overload.

Many times, the element has just a tiny break in it and you have to hold it up to a light to see it. It was stated that these fuses blew as they were designed to blow. That means that they opened in the middle of the element where it could clearly be seen in the viewing window.

In some instances (cheap AGU fuses, in particular), the fusible element will become desoldered from the end cap and the fuse will stop or intermittently pass current. This is what a blown ANL fuse looks like. Unlike other fuses that allow you to see through to the other side, you can't see an opening in the fusible element.

If you didn't look at the fuse before it was blown, it may be difficult to know if it was blown without using a multimeter to check it. There are several ways that you can check a fuse. When checking fuses in the circuit, you put one meter probe (meter set to DC volts) on each of the terminals and the meter should read approximately 0v DC.

When checking the fuses in the circuit and using the meter set to DC volts, the power should be as it would normally be when the fuse being tested had voltage on it. This means that if you're checking a fuse to see if it has voltage across it, and the fuse is used for something that only has power when the key is in the ign/on position, the key must be in that position. If it's not, there will be no voltage applied and there will be no voltage across the fuse, even if it's blown.

If the fuse reads something significantly higher than 0v, remove the fuse and check it out of the circuit. For this, you will set your meter to ohms. Touch the probes together to see what the meter reads.