K
can anyone give the detail of interposing relay... where it is used....
Sir can you please explain the "Driving Relay"?Excellent response, James.
I would just add a little clarification. Relays used as interposing relays are generally necessary because the circuit(s) being switched have voltages and/or currents which can't be accommodated by the "driving relay".
For example, let's say the relay of a PLC can only accommodate 0.5A at 220 VAC, but the solenoid which is to be connected to the relay requires 1.2A at 220 VAC. In this case, an interposing relay with contacts rated for operation at 1.2A at 220 VAC would be used as an interposing relay "between" the PLC relay and the solenoid. The coil of the interposing relay should require less voltage and current than the driving relay is rated for, and the contacts of the interposing relay must be rated to handle the requirements of the load (solenoid, light, contactor, motor, etc.).
As James says, many people ask why is the "second" relay necessary and I've seen them eliminated by site personnel, sometimes with catastrophic results. At one site, a 250 VDC solenoid coil drawing about 12.0 A was connected directly to a relay that was only rated for 3.2 A at 125 VDC, and an interposing relay which had experienced a couple of failed coils was eliminated. The PLC relay and the printed circuit card it was mounted on as well as the printed circuit cards on either side of the PLC relay card were all destroyed. It turns out that interposing relay manufacturer had produced a bad batch of relay coils causing the higher-than-expected failure rate of the interposing relay.
But, there are also applications which don't require interposing relays, but because they were part of a "standard" or generic design they were included with the equipment and do represent another possible point of failure. So, if you have questions, you need to consider the capability of the driving relay and the load before making any changes to existing circuits.
I hope this wasn't redundant, but just made things a little clearer.
Thread starter | Similar threads | Forum | Replies | Date |
---|---|---|---|---|
P | ESD system - Interposing Relay Panel - SIL Capable | Distributed Control Systems - DCS | 3 | |
T | Diagnostic Coverage for SIS Solenoid Through Interposing Relay | General Automation Chat | 3 | |
T | Wiring of Interposing Relay | General Automation Chat | 5 | |
T | Interposing Relay Testing | Power Generation | 3 | |
A | Interposing relay Panel | Process Control | 7 |