The house is protected: automatic fuses, difavtomatov and RCD

The house is protected: automatic fuses, difavtomatov and RCD

In recent years, intra-house elec­tri­cal net­works have become much more com­plex, the load on them has increased sev­er­al times. The require­ments for pro­tec­tion devices have also increased — the noto­ri­ous “plugs” (pro­tec­tive cir­cuit break­ers for a screw car­tridge) are tech­ni­cal­ly out­dat­ed and are used less and less in EU. They were replaced by more mod­ern and advanced mod­u­lar cir­cuit break­ers mount­ed on a DIN rail.

The house is protected: automatic fuses, difavtomatov and RCD

First level of protection — circuit breakers

Devices of the first lev­el of pro­tec­tion — auto­mat­ic switch­es — basi­cal­ly pro­tect the intra-apart­ment wiring and pow­er receivers from the dam­ag­ing effects of high cur­rent, which occurs pri­mar­i­ly dur­ing a short cir­cuit. Accord­ing­ly, it is nec­es­sary to choose a device depend­ing on the cross-sec­tion of the wire and the way it is laid.

In every­day life, switch­es are used, designed for a rat­ed cur­rent from 6 to 32 A; this fig­ure must be indi­cat­ed on the prod­uct. Sim­plis­ti­cal­ly, we can assume that 6 and 10 A machines are used in light­ing net­works with a small load (less than 1 kW for a sin­gle-phase 220 V net­work). 16 A machines are installed in apart­ments most often. For par­tic­u­lar­ly pow­er­ful equip­ment (for exam­ple, instan­ta­neous water heaters), auto­mat­ic machines of 32 A or more will also be required.

The house is protected: automatic fuses, difavtomatov and RCD

What hap­pens to the cir­cuit break­er when the load in the net­work reach­es a dan­ger­ous val­ue? The wire starts to heat up. The device includes a ther­mal release with a bimetal­lic plate. When a cer­tain tem­per­a­ture is reached, it acts on the cocked shut­down mech­a­nism, which breaks the con­tact. If the load slight­ly exceeds the nom­i­nal, the machine does not turn off soon. But when the load is twice the nom­i­nal, the shut­down will fol­low in a few sec­onds.

The house is protected: automatic fuses, difavtomatov and RCD

To turn off the net­work dur­ing a short cir­cuit, anoth­er release is used — elec­tro­mag­net­ic. It cuts off the cur­rent almost instant­ly — in mil­lisec­onds. At this moment, a very large short-cir­cuit cur­rent pass­es through the machine — thou­sands of amperes. House­hold mod­els of auto­mat­ic machines are usu­al­ly designed for a max­i­mum short cir­cuit cur­rent of 4500 or 6000 A. If it is high­er, then the release will not be able to break the cir­cuit.

When choos­ing a cir­cuit break­er, in addi­tion to the rat­ed cur­rent, pay atten­tion to the type of dis­con­nec­tion. It is denot­ed by the Latin let­ters B, C (devices of oth­er types are not found in every­day life) and means the max­i­mum load that the machine can with­stand with­out trig­ger­ing the elec­tro­mag­net­ic release. Type B devices can with­stand 3…5 rat­ed loads before dis­con­nect­ing the cir­cuit, and type C — 6…10 rat­ings. Type C automa­ta are used in cas­es where there are pow­er­ful elec­tric motors that can cre­ate an addi­tion­al (so-called reac­tive) load at start­up.

Do not try to con­nect all sock­ets and appli­ances through one switch. It is desir­able that each group of devices has its own machine.

What do power outages indicate?

Many users do not pay atten­tion to the fre­quent trip­ping of cir­cuit break­ers, which is one of the most com­mon mis­takes in every­day life. Reg­u­lar­ly “knocks out traf­fic jams”?

Per­haps they are weak, can not cope with the load.

This con­clu­sion is made by the home­own­er and goes to the store for a more pow­er­ful machine — by 20, 25, and prefer­ably by 32 A. Keep in mind: you can­not replace machines with­out con­sult­ing an elec­tri­cian! More­over, shut­downs should not be ignored. As a rule, they sig­nal that some sec­tion of the wiring is dam­aged or can­not cope with the load. If you sim­ply replace the machine with a more pow­er­ful one, then the dam­aged wire will heat up and col­lapse even faster.

How to prevent current leakage?

Cir­cuit break­ers are basic pro­tec­tion against short cir­cuits and net­work over­load.

Unfor­tu­nate­ly, elec­tric­i­ty can also car­ry oth­er dan­gers that oth­er devices are used to pre­vent.

Elec­tric shock pro­tec­tion. Units of the sec­ond lev­el — resid­ual cur­rent devices (RCDs) — appeared in the 70s. 20th cen­tu­ry and has since been wide­ly used in devel­oped coun­tries. By deter­min­ing the dif­fer­ence in cur­rent strength in the live con­duc­tor and the neu­tral con­duc­tor, the RCD is able to detect the cur­rent that flows along an unin­tend­ed route (neu­tral). If the leak­age cur­rent (dif­fer­en­tial cur­rent) reach­es a pre­de­ter­mined val­ue, the RCD trips and opens the cir­cuit. The response time should be as short as pos­si­ble (for most devices it is a few mil­lisec­onds). The main cri­te­ri­on for choos­ing an RCD for the con­sumer is the amount of leak­age cur­rent (it is indi­cat­ed on the case).

The most sen­si­tive mod­els oper­ate at a cur­rent of 10 mA. Such an RCD can be rec­om­mend­ed for instal­la­tion in wet rooms (bath­room, sauna) or, for exam­ple, in a nurs­ery. How­ev­er, a high­ly sen­si­tive device can even respond to the con­nec­tion of suf­fi­cient­ly pow­er­ful (2–3 kW) equip­ment. There­fore, in every­day life it is com­mon­ly accept­ed to use an RCD that oper­ates at a leak­age cur­rent of 30 mA. Its effect is quite notice­able, but it is con­sid­ered safe for a healthy adult under nor­mal con­di­tions (at room tem­per­a­ture and low humid­i­ty). But such a cur­rent allows you to con­nect suf­fi­cient­ly pow­er­ful equip­ment to the net­work.

The house is protected: automatic fuses, difavtomatov and RCD

How to use RCD correctly?

The resid­ual cur­rent device needs reg­u­lar per­for­mance mon­i­tor­ing. The lat­ter, how­ev­er, will not be dif­fi­cult — once a month you need to press the but­ton locat­ed on the RCD case. A healthy device will turn off and turn off the volt­age.

Fire pro­tec­tion. Devices of the third lev­el of pro­tec­tion — fire dif­fer­en­tial load switch­es. In fact, they are the same RCDs, but with a high­er trip cur­rent (hun­dreds of mil­liamps). Such switch­es are designed to pro­tect against the neg­a­tive effects of hid­den wiring dam­age.

For exam­ple, a con­duc­tor broke in some area, the screw clamps on the sock­et ter­mi­nals loos­ened (they need to be tight­ened reg­u­lar­ly, but few peo­ple do this) — accord­ing­ly, the con­duc­tive abil­i­ty wors­ens, the dam­aged area begins to warm up. The heat can be strong enough to even­tu­al­ly lead to a large leak­age cur­rent and a fire. Fire pro­tec­tion dif­fer­en­tial switch­es respond to such leak­age. These devices can be rec­om­mend­ed to own­ers of old hous­es with dilap­i­dat­ed wiring.

The first three lev­els involve pro­tec­tion from prob­lems asso­ci­at­ed with inter­nal fac­tors. The next two lev­els are pro­tec­tion from adverse exter­nal influ­ences.

The house is protected: automatic fuses, difavtomatov and RCD

Over volt­age pro­tec­tion. If instead of 220 V, 250–280 V is sud­den­ly sup­plied to the net­work, then house­hold appli­ances can mas­sive­ly fail. Many man­u­fac­tur­ers, know­ing about the unpleas­ant fea­tures of domes­tic net­works, sup­ply their equip­ment with built-in pro­tec­tion, how­ev­er, spe­cial devices of the fourth lev­el — dif­fer­en­tial switch­es (RCD with over­volt­age pro­tec­tion) — pro­vide effec­tive pro­tec­tion for all house equip­ment.

SPDs must be installed in all build­ings with light­ning rods, as well as in hous­es with over­head pow­er lines locat­ed in areas where thun­der­storms are fre­quent (more than 20 hours per year).

Surge pro­tec­tion. Appro­pri­ate devices of the fifth lev­el (the so-called SPDs) pro­tect the inter­nal elec­tri­cal net­work from the effects of pow­er­ful (thou­sands of volts), but extreme­ly short in time (of the order of microsec­onds) volt­age surges that are detri­men­tal to sen­si­tive elec­tron­ic equip­ment.

Circuit breaker selection parameters depending on the type of electrical appliances and the nature of the load

Elec­tri­cal appli­ance (device) pow­er, kWt Rat­ed cur­rent of the cir­cuit break­er, A Shut­down type
Fridge 0.3…0.5 6 FROM
Stor­age type water heater four twen­ty AT
Instan­ta­neous water heater 6 32 AT
Kitchen sock­ets (elec­tric ket­tle, toast­er, bread machine) 2 ten AT
Air con­di­tion­er 3.5 twen­ty FROM
Wash­ing machine 2.5 16 FROM
elec­tric stove 5 25 AT

Devices of each lev­el of pro­tec­tion solve their own range of tasks and, by and large, do not inter­sect with devices of oth­er lev­els. How­ev­er, some of them can per­form the func­tions of sev­er­al lev­els of pro­tec­tion. For exam­ple, there are so-called difau­tomats, which are a com­bi­na­tion of auto­mat­ic switch­es and dif­fer­en­tial cur­rent switch­es, that is, devices of the first and sec­ond lev­els. They are rec­om­mend­ed to be used, in par­tic­u­lar, when there is an increased risk of a short cir­cuit to earth. For exam­ple, street seg­ments of the elec­tri­cal net­work (gar­den sock­ets and light­ing ele­ments) are equipped with difav­tomata­mi.

All devices must be con­nect­ed in strict sequence, in accor­dance with the rec­om­men­da­tions of man­u­fac­tur­ers and the require­ments of GOST R 51628–2000 “Dis­tri­b­u­tion boards for res­i­den­tial build­ings”. Wiring dia­grams can be com­plex, so leave the job to a qual­i­fied elec­tri­cian.

All mod­ern cir­cuit break­ers are quite com­plex devices, when con­nect­ed, polar­i­ty, input and out­put ter­mi­nals must be strict­ly observed, and also not to con­fuse, say, phase and neu­tral. Unfor­tu­nate­ly, RCDs and oth­er devices are often con­nect­ed incor­rect­ly. In such cas­es, the RCD will not work and, most like­ly, will fail. When prop­er­ly con­nect­ed, all devices, as a rule, serve “from repair to repair”.

Break­downs usu­al­ly occur due to some exter­nal cause. For exam­ple, too much short-cir­cuit cur­rent when the con­tacts open caus­es a pow­er­ful spark, sim­i­lar to a weld­ing arc. In gen­er­al, each oper­a­tion of the machine slight­ly reduces its resource. There­fore, do not use pro­tec­tive devices as mains switch­es. For pow­er man­age­ment, it is best to install spe­cial cir­cuit break­ers. If there is no such switch, then before turn­ing off the pro­tec­tive devices, dis­con­nect the entire load from the net­work, turn off the equip­ment and light­ing.

One of the most com­mon myths is that RCDs do not work in a two-wire net­work (with­out ground). In fact, if there is no earth, then RCDs can not only be installed, but nec­es­sary! If, say, some­thing goes wrong in a wash­ing machine with­out a short cir­cuit (on a 220 V case), its oper­a­tion with­out an RCD will be dead­ly.

Sergei Akin­feev

Easy9 launch man­ag­er, schnei­der elec­tric

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