SOT Relay wireing question

OK, I have seen this many times in the past, but I am not sure of the exact reason for doing it. When wiring a relay socket base, why is there a diode between 13 and 14 (coil wires) I have seen them wired this way, and seen them wired without it. I am replacing some socket bases due to broken din rail hooks, and the locations for 13 and 14 are in different places on the new socket base, consequently the old diode leads are not long enough, are these even needed?

The diode is placed there to absorb / limit the counter-electromotive force generated when the magnetic field around the coil collapses. This is for the protection and to increase life of the contacts supplying the signal to the relay coil.

Diodes are used for DC relay coils and RC (resistor-capacitor) suppressor devices are used for AC relay coils. Please note that diodes are polarity sensitive while RC devices are not.

The diodes also protect your outputs on your PLC cards if that is what is firing the relay.

Think of it this way (some one told me this and I think it is the best anology). Imagine the spark plug in your car. That spark is the result of the feild colasping in the coil. Now imagine that going backward into your circuit. The diode bleeds this power off helping your equipment last longer.

You do not absolutly have to have it but it is a nice insurance policy.

FYI.... you can find this diode on solenoids also and it does the same thing.

tacm, in attached file you have a complete explanation. It is an academic approach to the problem.
I hope you'll be satisfied with the answer....

Merry Christmas to all!

Best regards,
Pandiani