Device and use of safety fuses
The safety fuse is the simplest device for protection of electric units against big overloads and short circuits. In all cases when safety locks can provide necessary sensitivity of protection, it is recommended to use them instead of automatic cuts. The rated current, rated voltage and extremely disconnected current belong to key parameters of safety locks.
The principle of operation of the safety lock is simple.
Its fusible insert at course of current on it heats up. During the overload or the short circuit it fuses. The current circuit at the same time is broken off. That at burn-out of the fusible insert there was no dangerous electric arc which can damage the equipment or constitute danger to service personnel, it is located in porcelain tubes. Fusible inserts of safety locks make of lead, its alloys, zinc, aluminum, copper, silver.
Fusible inserts from lead and its alloys have low melting temperature and also possess the thermal lag in view of the big specific heat capacity of these metals. Therefore short overloads do not disconnect such fusible inserts. But, on the other hand, because of rather high unit resistance of these materials the section of fusible inserts on big currents turns out big and at their burn-out the large amount of metal is sprayed. The scope of such inserts — tension up to 500 Century.
On the design safety locks can be threaded type (plug) or tubular. The basis is plastic, fastens to the load-carrying structure the screw. In the tube (VTF) there is the dry quartz sand. The tube is established in the safety lock cover opening.
For normal safety locks, except traffic jams with fusible inserts plug automatic machines which are screwed in the same basis instead of traffic jams are issued. At the overload and short circuits in the line the automatic machine disconnects the line the contacts. The chain is recovered by pressing the button. The button serves, for shutdown of the chain (instead of the switch). Broad application is found by the AB-25 submachine guns.
For domestic needs switches with degrees of protection of IP 20 for the opened and closed electric conductings are issued. Besides for the buried wirings IP 54 switches can be used.
Big range of design features of switches and switches and also their external and color design allows to carry out their selection according to assignment, the room interior and also provides convenience and reliability at operation. Often use the switches and switches installed directly on the wire to portable and floor (floor lamps) lamps. They can be lever, push-button.
At direct placement on the lamp sometimes use cord switches. Keyboard mechanisms of switches use as wall more often. It is the best of all to install switches so that inclusion happened pressing of the upper button, impact on the upper of the key or transfer of the lever in upper situation (at application of lever products).Top