During an electrical emergency, what is the first step taken to respond?

The first step in responding to an electrical emergency on an Embraer Regional Jet (ERJ) is to deploy the Ram Air Turbine (RAT) automatically. The RAT serves as a backup power source, providing essential electrical and hydraulic power to critical systems in the aircraft when the normal power sources are lost. Deploying the RAT quickly restores some level of system operation, which is crucial for maintaining control of the aircraft and ensuring the safety of the crew and passengers.

The other options, while they may be necessary steps in particular scenarios, are not prioritized as the initial action. Connecting all buses to the main frames could be part of restoring power, but it does not address the immediate need for backup power. Isolating the main battery would further eliminate available power, making the situation worse initially. Shutting down non-essential systems could be a follow-up action to conserve power, but first, restoring power with the RAT is essential to maintain basic aircraft operations. Thus, deploying the RAT is critical in managing an electrical emergency effectively.