An electrical room is a Class C hazard, which is a statement about the ignition source rather than about the fuel. The energized equipment does not burn. What burns is cable insulation, wire jacketing, terminal blocks, and the accumulated dust and debris inside enclosures, all ignited by a fault that releases an enormous amount of energy in a very short time. Once the circuit is de-energized the fire reverts to an ordinary Class A fire in the insulation.
That distinction drives agent selection completely. Water and foam conduct, and applying either to energized gear creates a shock hazard for responders and a ground fault path that can propagate the fault. Dry chemical is non-conductive in the moment of discharge but leaves a hygroscopic, corrosive residue across every relay contact, bus connection, and control card in the room, which routinely converts a contained fire into a full switchgear replacement.
The dominant ignition mechanism is an arcing fault, and the conditions that produce one are almost always maintenance-related: loose connections that heat under load, tracking across surfaces contaminated by dust and salt-laden humidity, degraded insulation, and moisture intrusion. In coastal South Florida the salt content of the air and the humidity load make tracking and corrosion a materially larger contributor than in inland climates, which is why NFPA 70B maintenance discipline does more to prevent these fires than any suppression system does to control them.