Application of 4-pole switching devices


Most low voltage switchgear has three contacts in the main circuit, which switch three-phase loads on all poles. In some applications, switchgear with four main poles is required, either for safety reasons or for an optimal solution of the application.

This may require various device configurations.

Switchgear applications with 4 NO contacts

Four NO contacts are necessary or at least very advantageous for the applications below:

Request n ° 1

Applications requiring the interruption of the neutral line to switch off or disconnect loads. This may be the case in power supplies subject to unfavorable earthing conditions, in TT power supplies, for protective disconnection in computer networks or to impedance earth. Care must be taken that the neutral pole closes before or at the same time as the other poles and opens after them or at the same time.

When changing non-linear consumers, special attention should be paid to the current load of the neutral line.

The effect of higher frequencies on the performance of low-voltage devices should be taken into account both in networks with higher base frequencies (for example 400 Hz) and in cases where current harmonics occur. These current harmonics occur if the supply voltage contains harmonics or if non-linear consumers are connected.

Application of 4-pole
Application of 4-pole

These consumers can, for example, be compensation for devices for luminescent lamps operating in the saturation range or devices with phase shift control. With consumers with phase angle control and with frequency converters, harmonics with frequencies up to several khz may appear in the power supply. The harmonic content can be increased by capacitors connected to the power supply, the current consumption of which increases with increasing frequency.

This factor should be given special attention in individually compensated motors and it may be necessary to correct the current settings of the protection relay.

In applications where current harmonics occur, the effect of the harmonics ( eg additional heating effects ) is added to that of the base frequency. This can be particularly critical in devices containing coils of ferromagnetic materials (bimetal heating coils, magnetic triggers, etc.).

In the case of loads with connection to the neutral conductor ( eg. Single-phase loads such as luminescent lamps, small current adapters, etc. ), the formation of a zero-sequence system can lead to thermal overload can lead to high harmonic content. Should also be taken into account when using 4-pole switchgear. To get training of Auto

Application n ° 2

Switching of supply systems ( eg for emergency power supplies ), where complete separation of the two power systems is required.

Application no.3

Switching of several single-phase loads (heaters, lamps) with a switching device.

Application n ° 4

Switching of direct current loads with a higher nominal voltage requiring the series connection of four contacts.

Switchgear designed for alternating current can carry at least the same rated rated operational direct current. With direct current, the skin effect in the circuits disappears and none of the specific effects associated with alternating currents such as hysteresis or eddy current losses occur.

DC devices operating at low voltage can be switched by AC switchgear without difficulty , since their switching capacity for low voltage DC is practically the same as for alternating current.

With voltages above approx. 60 V, the DC switching capacity of the AC switchgear with double-break contacts (eg contractors) decreases sharply. By connecting two or three circuits in series this limit can be increased to two or three times the voltage.

The reason for the reduced switching capacity with direct current compared to alternating current is the absence of the current zero crossover, which in alternating current favors the quenching of the electric arc. The electric arc in the contact system can continue to burn under higher forward voltages and thus destroy the board.

With forward voltages, contact erosion and hence contact life also differs from that of alternating voltages. The possible values ​​for direct current are specifically tested and documented. With direct current, the load influences the switching capacity more strongly than with alternating current. The energy stored in the inductance of the load must be largely dissipated in the form of an electric arc.

Therefore with a strongly inductive load ( large time constant L / R ) the permissible switching capacity for the same electrical lifetime is lower than that of an ohmic load due to the much longer breaking times.

Switchgear applications with 2 NO contacts and 2 NC contacts

Devices with two NO contacts and two NC contacts are useful in applications where one of the two circuits must always be closed.

These are, for example:

Switchgear applications with 3 NO contacts and 1 NC contact

Devices with three NO contacts and one NC contact are used in applications where, when the main load is turned off, for example the motor, another single-phase load must be turned on.

These applications could include:

  1. Safety circuits
  2. DC braking systems activated when a driver is stopped
  3. Clutches that must be released when the drive is turned off

Leave a Comment

Your email address will not be published. Required fields are marked *

50% OFF ON ALL COURSES till 15 May 2022
This is default text for notification bar

of escort çukurova escort kozan escort seyhan escort yüreğir escort adana mutlu son masaj besni escort kahta escort gölbaşı escort adıyaman mutlu son masaj bolvadin escort dinar escort sandıklı escort emirdağ escort afyon mutlu son masaj diyadin escort doğubayazıt escort patnos escort ağrı mutlu son masaj ortaköy escort aksaray mutlu son masaj merzifon escort suluova escort taşova escort amasya mutlu son masaj çankaya escort keçiören escort yenimahalle escort mamak escort etimesgut escort sincan escort altındağ escort pursaklar escort gölbaşı escort polatlı escort çubuk escort kahramankazan escort beypazari escort ankara mutlu son masaj alanya escort manavgat escort serik escort antalya mutlu son masaj şehitkamil escort nizip escort ıslahiye escort antep mutlu son masaj ardahan mutlu son masaj artvin mutlu son masaj hopa escort borçka escort aydın mutlu son masaj efeler escort nazilli escort kuşadası escort söke escort didim escort incirliova escort çine escort germencik escort balıkesir mutlu son masaj karesi escort altıeylül escort edremit escort bandırma escort gönen escort ayvalık escort burhaniye escort bigadiç escort susurluk escort bartın mutlu son masaj batman mutlu son masaj kozluk escort sason escort beşiri escort bayburt mutlu son masaj bilecik mutlu son masaj bozuyuk escort bingöl mutlu son masaj solhan escort genç escort karlıova escort bitlis mutlu son masaj tatvan escort güroaymak escort ahlat escort bolu mutlu son masaj gerede escort burdur mutlu son masaj bucak escort bursa mutlu son masaj osmangazi escort yıldırım escort nilüfer escort inegöl escort gemlik escort mudanya escort mustafakemalpaşa escort gürsu escort karacabey escort orhangazi escort kestel escort iznik escort çanakkale mutlu son masaj biga escort can escort gelibolu escort ayvacık escort çankırı mutlu son masaj çerkes escort çorum mutlu son masaj sungurlu escort osmancık escort alaca escort iskilip escort denizli mutlu son masaj pamukkale escort merkezefendi escort çivril escort acıpayam escort tavas escort diyarbakır mutlu son masaj kayapınar escort bağlar escort yenişehir escort ergani escort bismil escort sur escort silvan escort çermik escort dicle escort düzce mutlu son masaj akçakoca escort kaynaşlı escort edirne mutlu son masaj keşan escort uzunköprü escort ipsala escort elazığ mutlu son masaj kovancılar escort karakoçan escort erzincan mutlu son masaj erzurum mutlu son masaj yakutiye escort palandöken escort aziziye escort horasan escort oltu escort pasinler escort odunpazarı escort tepebaşı escort eskişehir mutlu son masaj bulancak escort espiye escort tirebolu escort görele escort giresun mutlu son masaj gümüşhane mutlu son masaj kelkit escort hakkari mutlu son masaj yüksekova escort şemdinli escort hatay mutlu son masaj antakya escort iskenderun escort defne escort dörtyol escort samandağ escort kırıkhan escort reyhanlı escort arsuz escort altınözü escort hassa escort payas escort erzin escort yayladağı escort ığdır mutlu son masaj yalvaç escort eğirdir escort sarkıkaraağaç escort ısparta mutlu son masaj istanbul mutlu son masaj izmir mutlu son masaj buca escort karabağlar escort bornova escort karşıyaka escort konak escort bayraklı escort çiğli escort torbalı escort menemen escort gaziemir escort ödemiş escort kemalpaşa escort bergama escort menderes escort aliağa escort tire escort