Selective circuit breaker

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Selective miniature circuit breakers in a block of 3, the left one has a transparent housing half for teaching purposes

A selective line circuit breaker (SLS switch) , depending on the manufacturer, also a selective main line circuit breaker ( SH switch, SHU switch), is a special line circuit breaker that meets selectivity requirements for upstream and downstream overcurrent protection devices. This means that in the event of a short circuit , an SLS switch does not switch off immediately like other miniature circuit breakers, but with a delay, which means that downstream fuses or normal miniature circuit breakers always switch off beforehand. However, since these often have insufficient switching capacity for the large short-circuit currents in low-impedance (i.e. strong) networks, the SLS switch immediately limits the current by inserting a current-limiting resistor.

SLS switches are used instead of the previously usual fuses in front of electricity meters from energy supply companies . For Germany it was planned to introduce the SLS switch with the TAB 2000 . Due to a lawsuit against the VDEW sample wording of the TAB 2000, § 7.4 (2), and a settlement proposed by the court, which was accepted in December 2005, the TAB has been revised. Since then, a "selective overcurrent protection device" has to be provided in the lower connection area of ​​the meter space, whereby the SH switch is only given as an example in brackets; accordingly, other selective solutions for short-circuit protection are also permitted. Today, the SLS switch replaces the Neozed switch disconnectors (Linocur switches) that were previously used in new systems , the NH fuses or the large Diazed fuses that were used even earlier (the latter both also known as "armored fuses").

Like other miniature circuit breakers, SLS switches are equipped with a toggle switch that can be used to switch the system manually without exposing live parts such as fuses. SLS switches may therefore also be operated by people who are not qualified electricians. One therefore also speaks of the “lay-user activation option for the customer system”. They can usually be locked and provided with a seal .

Layout and function

Selective miniature circuit breaker with transparent housing for teaching purposes, side view

In the adjacent picture:

  1. Arc extinguishing chamber (1 of 2)
  2. Main contact 25 kA (1 of 2)
  3. Actuating coil for main contacts (main current path)
  4. Current limiting resistor (auxiliary current path)
  5. thermal overcurrent release (bimetal in the main current path)
  6. thermal delayed release in the event of a short circuit (bimetal in the bypass current path)

The contact for the delayed (final) shutdown is covered.

In the event of a short circuit, the main current contacts open immediately using the actuating coil and the current is limited by the wire resistor in the auxiliary current path. The current now flows through the narrow bimetal in the auxiliary current path and after a short time triggers the switching mechanism, which opens a contact in the auxiliary current path. If the short circuit has already been eliminated within this period of time (e.g. because the downstream miniature circuit breaker has switched off), the main contacts close again and no tripping takes place.
The thermal overcurrent shutdown takes place with the (thick) bimetal, which, like the actuating coil, is traversed by the current.

Some models only switch on the main current path (again) automatically when a voltage to earth occurs. This prevents the unlimited current from flowing in the event of a short circuit when switched on by hand. Furthermore, the current limitation is not ended when the current falls below the trigger value, but only when the voltage at the outlet returns.

There are tripping characteristics E and Cs, which differ in that Cs is used for higher starting currents, e.g. B. of engines is suitable.

See also

Individual evidence

  1. ↑ BDEW: Legal notice to § 7.4 (2) of the VDEW sample wording of the TAB 2000, taking into account the specifications of the comparison to the SH switch ( memento of the original from July 2, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and still Not checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.bdew.de
  2. ↑ Technical information on § 7.4 (2) of the VDEW sample wording of the TAB 2000, taking into account the specifications of the comparison to the SH switch Online available at the Forum Netztechnik / Netzbetrieb im VDE (FNN) (PDF; 54 kB)
  3. ↑ Hager SLS Exx series
  4. ↑ http://www.e-volution.de/files/download/0/1101_1/0/seiten_aus_katalog-hager_EV_ZP_sls-kap13.pdf (PDF, 393 kByte, page 10)