The specifications for all GIGAVAC relays, unless otherwise specified, are without the use of coil suppression. If you need to suppress the back EMF of the relay coil, GIGAVAC recommends the use of a zener-zener or diode-zener combination with the zener voltage at 2 times, or more, of the coil source voltage.
Other coil suppression techniques such as single diode, resistor capacitor combination, resistor, or varistor noticeably slow down the release time of the relay and can effect the life of the relay or the use of the relay in the application. In carry only applications, the release time may not be important so these less expensive coil suppression techniques can be used. However, if the release/reset time is important, or if the contacts are to interrupt a load, do not use these techniques and use the recommended zener-zener or diode-zener combination.