Electrical equipment will spontaneously ignite if it is not grounded due to leakage. It depends on whether there are combustible materials and whether the ignition point of combustible materials can be reached. If the ignition point is not reached, it will not spontaneously ignite.
Of course, when the heat dissipation of electrical equipment is not good, it will be overloaded and overcurrent for a long time, and it will spontaneously ignite when it reaches a certain temperature. This has nothing to do with grounding or not.