How to use the fuse correctly? In this article, we will talk about what is a fuse and present all types of fuses that exist. Let’s give fuse box tips, fuse holders and many other information about the applications of fuses, come on guys!
The correct choice of the fuse is very important because when the wrong dimensioning occurs, the risks and damages can be enormous. In order to define which fuse should be used, it is necessary to evaluate the operating conditions of the circuit that will be protected, in order to prepare this device in case it is requested in some overcurrent situation.
Fuse, what is it?
The fuses are composed of a conductor of a reduced section mounted on an insulating material base. The physical structure is the base that supports the fuse holder and the protection ring that aims to protect and avoid the contact of the base thread with the circuit. The fuse itself is the replaceable part and every fuse must have a description of the current value it supports expressed in its body.
Fuse: what is it for?
The short circuit can cause fires and various damages to electrical equipment and that is why fuses are so used. Fuses are devices used for protection against overcurrent, short circuit and long-term overload.
Fuse: how does it work?
The fuse is nothing more than a connecting link through which the current flows. Several fuses are made with a small low melting metal alloy, usually lead. The operation is very simple, when the intensity of the electric current exceeds the limit of that fuse, this alloy heats up well and melts, causing the interruption of the current flow.
So, when these conditions happen and the fuse blows, preventing the passage of electric current, in addition to preventing fire risks, there is also protection against damage to electrical and electronic installations and equipment.
But to guarantee this effective protection, it is essential that the capacity of the fuses is correctly sized, otherwise, if the fuse does not blow out when there is an overload, the circuit wiring and the devices connected to it, may suffer various damages.
Fuse: Important features
- Rated current: it is the current value that the fuse can withstand without blowing. This current information is usually described on the fuse body.
- Breaking current: the maximum current that the fuse can break.
- Conventional actuation current: it is the specific current value that causes the protection device to actuate in a determined time.
- Characteristic curve: it is the relation between the time required for the interruption in function of current.
Fuses can be classified as fast or delayed and this depends on the time of operation of each one. Delayed fuses are mostly used for motor protection because of the peak current that occurs at startup.
Another feature that differentiates one fuse from the other is the time it takes to blow. This time is proportional to the square of the applied current and the thermal inertia of the material used in the link. Exactly why the variation of the material used interferes with the action speed of that fuse, that is, the action speed can be very slow, slow, fast or very fast!
The category and specification of the fuse service classes is defined using two letters, the first being lower case and the second capital letter, as shown in the table below.
To better understand this usage according to the classification, we will show some examples.
- “AM” – The first letter is a lowercase a which indicates that the performance is against short. The second letter is a capital M which indicates that this fuse is for motor protection.
- “GL / gG” – The first letter is a lowercase g which indicates that the actuation is against overload and short. The second letter is L and G which indicates that this fuse is for cable protection and general use.
- “AR” – The first letter is a lowercase a which indicates that the performance is against short. The second letter is a capital R that indicates that this fuse is for semiconductor protection.
NH type fuse – These fuses are used in industrial electrical installations to protect against short-circuit overcurrents. They have the use category “gL / gG”, and can be found in 6 different sizes, meeting the nominal current from 6 to 1250A. NH fuses are current limiters with high breaking capacity, which can be 120KA at up to 690VAC.
Type D fuse – These fuses are used for short circuit protection in electrical installations. They have a “gL / gG” utilization category, and can be found in 3 different sizes, meeting the nominal current from 2 to 100A. D fuses have a breaking capacity of 20A – 100kA, 25 to 63A – 50 to 70kA.
There are several types of fuses and if you have understood the information, you will know that its use depends on the category, the rated current and the breaking capacity. So just look at each of these points in detail and you will certainly choose the correct fuse.
Finally, we want to leave a very important explanation, the use of fuses for short circuit protection is very efficient, but not for overload protection, because the current intensity can be 1 to 4 times its nominal value. Therefore, for protection against overload, the most suitable is to use circuit breakers.v