leading contact
A and C: normal normally open contact, e.g. B. contacts 1 and 2 or 13 and 14 in a relay
E: early make contact, e.g. B. Contacts 37 and 38
F, G: Overlapping NC and NO contacts
In the field of electrical engineering , leading contact means that the electrical connection of a specific contact of a connector or switch is established before the connection of all other contacts. Similarly, when the connections are disconnected, the one of the leading contact is the last to be interrupted.
Areas of application
The examples listed below are not intended to suggest that longer contacts / pins necessarily indicate a leading contact. Rather, the exact execution of both sides of a contact must be taken into account.
- In the case of mains plugs (e.g. Schuko plug connector), the protective conductor connections are leading, so that the device to be connected is earthed when plugged in before the connection to live conductors of the power supply is established. There are three stages with the CEE three-phase connector: First the protective conductor connection is established, then the connection for the neutral conductor , and only at the end are the external conductors contacted. This avoids a neutral point shift with its risk of overvoltages during the contacting process. The order is determined by a suitable combination of pins of different lengths and contacts recessed to different depths on the socket side.
- The same applies to some audio connections, such as the XLR plug connector, where the shield contact leads the signal contacts. In contrast, it behaves in the RCA connector , the shield lags (except in special versions).
- In the case of a residual current circuit breaker , the connection of the outer conductor (s) is first disconnected during the shutdown process , followed by the connection of the neutral conductor . The switch-on process is reversed, that is, the neutral conductor contact is connected leading .
- In contactor and relay circuits in automation technology, NC contacts are leading: The circuits to be opened are disconnected before the circuits to be closed are connected, see also switches , contactors and relays .
- Certain hot-plug- capable systems such as USB and Serial ATA use leading contacts in the connector for the supply voltage , so that this is already present when the data connection is established. This avoids a latch-up effect .
USB plug with clearly visible leading external contacts for the supply voltage, while the data connection uses the middle contacts behind.
Leading Serial ATA connectors (pins 1, 4 and 7).
The cinch plug is an example of leading contacts that are not adapted to the application: the leading inner contact causes unpleasant mains hum when pulling or plugging in, if only the inner conductor is in contact .
Individual evidence
- ↑ moeller (PDF; 508 kB): Projecting with mechanical auxiliary contacts in compliance with standards and functionally reliable , 4-pole switching with DILMP contactors , manufacturer itself