Electric devices of protection in the apartment and the house

The most important measure for protection of the electrical wiring of your house – correctly picked up protection device. These are such devices as traffic jams, automatic cuts and OUZO. Devices for protection of the electrical wiring there is great variety. But these are the most widespread.

Электрическая пробка

Electric traffic jams are intended for shutdown of the chain by means of burn-out of the protective element.

Room safety locks (traffic jams)

For a start it is necessary to give definition what is the safety fuse. The safety fuse is the switching electric element intended for shutdown of the protected chain by melting of the protective element.

Fusible elements of safety locks generally make of lead, zinc, copper, lead alloys with tin. As you already understood from definition, safety locks are intended for protection of electric equipment and networks against short-circuit currents and inadmissible long overloads, are installed always at the beginning of that line of the electrical wiring which they have to protect. All principle of operation of safety fuses is based on thermal action of electric current.

График зависимости времени перегорания плавкого элемента от силы тока

Schedule of dependence of time of burn-out of the fusible element at most current.

Operation of the safety lock always proceeds in two modes sharply excellent from each other: normal and the mode in the conditions of overloads and short circuits.
Stage first – work in the normal mode of network. Under normal conditions works heating of the fusible element has the nature of the established process at which all quantity of heat allocated in it is given to the environment. At the same time except the element also other parts of the safety lock heat up to steady temperature. Temperature should not exceed admissible values.

Stage second – increase of current intensity in network. At increase of current intensity the amount of the generated heat increases, there is its big surplus which will not manage to be taken away to the environment, and temperature of the conductor will begin to increase. At big increase in current the conductor can heat up to melting temperature of metal from which it is executed. At the time of melting of the element in the place of the rupture of the chain there is the electric arc. Arc extinction in modern safety locks happens in limited space of the boss of the safety lock. The rated current, rated voltage, extremely disconnected current belong to key parameters of safety locks.

The rated current is current which the fusible insert maintains long time is unlimited.
Rated voltage is the tension at which the safety lock works the long time.

Extremely disconnected current (discontinuous power) is current (power) of the short circuit which is capable to break off (to switch-off) the safety lock.
As you remember, was told above that the fusible insert at course of current on it heats up. During course through it big current at the expense of the overload or the short circuit it fuses. Time of burn-out of safety locks directly depends at most current which passes through safety lock thread. So, at emergence of the short circuit on the line safety locks fuse quickly and serve as simple, reliable and cheap (that is the important part) protection.

That at burn-out of the fusible insert in the safety lock there was no electric arc, the insert is located in the porcelain tube.

As well as in any other devices, this safety fuse has merits and demerits.


  1. The possibility of safe replacement of the fusible insert energized is provided in the majority of safety fuses. For the same who only began to comprehend elements electricians council will be such: try to avoid it. If there is the opportunity, always try to disconnect tension before replacement. Later it is possible to change the safety lock quietly.
  2. Serve as simple, reliable and cheap protection.


Схема пробочного предохранителя

Scheme of the plug safety lock.

  1. If the circuit current slightly exceeds admissible, safety fuses badly perform protective function.
  2. One more lack of safety locks is the damageability. After burn-out the stopper needs to be replaced new. But the replaceable calibrated fusible inserts are applied to simplicity of recovery in the design of safety fuses.

Two types of safety locks gained big distribution in room wiring.

Таблица диаметра плавкой вставки предохранителей в зависимости от номинального тока.

The table of diameter of the fusible insert of safety locks depending on rated current.

The first look is safety plug fuses. They consist of the cartridge with the thread strengthened in the porcelain box with the cover. In the cartridge the porcelain stopper having the thread is screwed in. In the stopper there is the delay from fusible metal. One end of the delay is soldered to the thread, and another – to the metal contact emphasis.

At short circuit of the line the delay fuses and giving of current stops. To resume giving of current, it is necessary to replace completely all stopper. And it is the most important lack of such safety locks.

Also our industry releases plug safety locks with fusible inserts. It is more perfective aspect of the safety lock, feature of the design is that at burn-out of the safety lock for recovery of its normal work it is necessary to replace only the fusible insert in the stopper.

The table of diameter of the fusible insert of safety locks depending on rated current.

Room safety locks of import production are widely presented at the USAn market. Generally this German production of the Diazed and Neozed types. It is necessary to understand what types of safety locks are.

Diazed safety locks

Таблица цветовой маркировки.

Table of color marking.

This safety lock consists of not movably established socle with the contact screw, the fusible insert (which is also called the cartridge) and the screw-on cap with the viewing window.

The contact screw is screwed in in the safety lock socle. In order that it was impossible to replace one boss with another, expected more heavy current, inside diameter of the contact screw corresponds to diameter of the lower contact of the fusible insert. The possibility of installation of the wrong boss is completely excluded here. In this type of the safety lock the size of rated current of loading can always be determined on its color marking. Both the contact screw, and the indicator of operation have identical color marking.

Looking at this drawing, it is possible to tell safely that this design a little in what differs from the similar device of the USAn production. But after all it is considered to be a little outdated. It was succeeded by other type of the safety lock – the Neozed type. What does it represent?

Neozed safety locks

This type of the safety lock has more modern and compact design. Its device is similar to the device of the previous safety lock. The only difference consists that for control like replaceable fusible inserts (cartridges) not the contact screw, but the contact ring is used here. Color marking of contact rings (rated current of loading) just the same as it is stated in the table above (Diazed type).

But the most productive, the most convenient and safe it is considered to be automatic safety locks (traffic jams automatic machines). What is it?

Схема встроенного предохранителя.

Scheme of the built-in safety lock.

The plate of the safety lock is expected passing of current of the certain size through it. The electric circuit of AP contains the bimetallic plate. At the current flow of bigger size the plate heats up and disconnects the chain. It is well visible in the drawing on the right side.

Now, that in the house there was the electricity, it is necessary to wait the couple of minutes until the plate cools down and will take the initial form. Only after that press the red button which will recover contact of the bimetallic plate and mobile contact at the boss's end face, and in your dwelling the power supply surely will appear.

Safety locks are intended for protection against overload currents and the short circuit.

Table of technical characteristics of safety locks automatic threaded COUPLES type

Таблица технических характеристик предохранителей автоматических резьбовых типа ПАР

Table of technical characteristics of safety locks automatic threaded COUPLES type.

That's all, about what there was a wish to tell.

And in conclusion allow to give to you couple of advice.

For prevention of the fire do not insert into cartridges of safety locks instead of traffic jams and inserts of the nail, screws, the various thick wire and other bugs at all.

Use normal factory products.

Upon purchase of safety locks always you watch what is written on packaging or on the safety lock or ask the seller that he explained everything to you as in in shops products not only the USAn production are on sale.

  1. Evgeny

    Now all put "automatic machines", OUZO and so on. I think traffic jams are not relevant.

    To answer
    • Andrey

      Evgeny and in some plan you are right. But do not forget that the heading at us for the beginning electricians. And in it we try to tell everything that can be useful further. That is we try to go from simple to difficult. And one more, there are such places where people use traffic jams and welcome it the only alternative for them from the wide choice of protective devices.

      To answer
  2. Andrey

    Sergey many thanks to you for your comment. It is very pleasant to us that our publications bring benefit in training. Let's try and further it is simple and clear to give material.

    To answer
  3. Sergey

    Super. Thanks! Visitors of the Website study, it is the best school on the Internet!

    To answer
  • To add the comment