The option to cut power are negotiated into the service contracts.

For instance an aluminum smelter may need a certain amount of notice to shut down their machinery, so they may negotiate an hour of notice or whatever they need. The power company may have to briefly load shed residential while still in the notice period, but then they take the smelter offline and restore service.

I find it highly likely that high consumption electric car fast charging site would negotiate to be the first in line to have their power cut given they don't have any equipment that could be damaged and they'd be most interested in discounted power.

I was remembering how critical infrastructure stays on. Most critical infrastructure is commercial.

However, a business park or an office block gets cut off with the homes.