Remember, as a thumb rule, that whenever the inductive load is used in the circuits; depending upon the nature of the load, there can be or can not be a need for a snubber circuit. Snubber circuit is basically used to cater for the dv/dt and di/dt side effects. We mostly used capacitors and inductors in designing snubber circuits. Usually a RC snubber is used with the thyristors so that false turn on of the thyristor due to the high dv/dt can be avoided. The values of these passive components are calculated depending upon the load and the selection of components. Since most of the AC loads are inductive in nature, so there is often a need of the snubber circuit with MOC3021 and BT136. Here is the modified version the MOC3021 circuitry for an inductive load.
Here you can see that there are snubber circuits, one for the triac and the other for the opto triac. A combination of 39 ohm resistance and 0.01u is a protection for the triac BT-136, similarly 470 ohm/0.05 u is for the opto triac. The above circuit had been tested practically.
More to follow.