Contactor

[arunavac]

please tell me about contact multiplication in any control circuit and what do u mean by main contact and aux. contact?

 

[charlie b]

A “contactor” is essentially a coil of wire that, when energized, creates a magnetic field that causes its contacts to move. This can cause two contacts to touch each other, thus completing a circuit, or can cause two contacts that had been touching each other to move away from each other, thus opening a circuit. It can also be set up to do both (i.e., open one set of contacts and close another set of contacts). There will be one or more springs that would pull the contacts in one direction, and the magnetic field from the coil will pull them in the other direction. Thus, with the coil deenergized, the contacts are in one configuration, and with the coil energized they move to the opposite configuration.

You can set it up so that a “main” set of contacts does one job (such as turning on a motor), while at the same time one or more other sets of contacts (“auxiliary contacts”) are doing other jobs (e.g., turning on a light to tell you that the motor is running). You can use a single contact, such as from a pressure switch or a level switch, to energize a coil of a contactor, and then have several sets of contacts from that contactor to do a number of jobs. That is what is meant by “contact multiplication.”

 

[LarryFine]

You can use a single contact, such as from a pressure switch or a level switch, to energize a coil of a contactor, and then have several sets of contacts from that contactor to do a number of jobs. That is what is meant by “contact multiplication.”

This is accurate. (Not to imply the rest wasn't. )

I did a Google search for "contact multiplication" and Google completed it with 'relay' added on. The first link was to an ABB site, and the text described using a multipole relay to "add" contact sets to a controller.

We're basically doing the same thing any time we use a 2p or 3p contactor to energize line-to-line loads (in addition to the current capacity benefit.) A lighting contactor is another (and expensive!) example.

 

[rcwilson]

In hard-wired relay control circuits (as opposed to programmable logic circuits like a PLC) a contact multiplier is used to send the same logic signal to different circuits. It is just a relay with multiple contacts.

Example: Imagine a conveyor system that when the conveyor is running needs to sound a 24 V alarm horn, flash a 120V beacon, and signal the upstream conveyor that it is OK to sending product down to this conveyor. That's three signals at different voltages going to three different circuits.

But your conveyor motor starter only has the three Main Contacts that power the 3-phase conveyor motor and one Auxiliary Contact that mimics the main contacts - it closes when the motor is running.

You need a contact multiplier to get three signals from the one auxiliary contact. You wire the aux contact to energize a relay coil that operates three contacts.

In the utility world, a circuit breaker has main contacts that make and break the high voltage current. The circuit breaker mechanism has auxiliary contacts that indicate whether the breaker is open or closed. In some protection schemes, more contact signals are needed than are available on the breaker, so a contact multiplying relay is used.

In critical circuits, the contact multiplying relay can add another source of failure if the coil fails. The signal from the failed relay might indicate the breaker is open when it is really closed. Good engineers design the circuits to be failsafe when failures like this occur.

 

[billsnuff]

To continue where Charlie left off:

I have a machine that has a start relay the changes the state of 6 circuits, 4 NC and 2 NO, the relay for slow speed has 7, 3 NC and 4 NO, and splice speed also has 7 3 NC and 4 NO.

3 contact relays 24 circuits.......