Is wearing a suit and tie considered imitation of the disbelievers, and how do we distinguish between blameworthy imitation and other types?

Nothing is forbidden merely because disbelievers do it. The prohibited imitation is in doing what is specific to their religion or customs, such that anyone who sees it would think that the person belongs to them. As for things that have become widespread among people and no longer distinguish non-Muslims, like ties and suits, these do not fall under the prohibition.

The use of electricity and modern inventions does not fall under the category of imitation at all, as the Prophet, peace and blessings be upon him, adopted the Persian stratagem of digging the trench. Sheikh Ibn Uthaymin is of the view that imitation of disbelievers is for a person to dress in their attire such that when a viewer sees him, he says: "This person is one of the disbelievers." However, what is common among Muslims and disbelievers is not imitation.