NSA has very strict power filtering rules for their Red/Black systems. Their building is covered in a copper Faraday cage. They also have a double outer shell,

NSA has very strict power filtering rules for their Red/Black systems. Their building is covered in a copper Faraday cage. They also have a double outer shell, with space between the two walls, where speakers play white noise. All this is public knowledge for many decades now. Food for thought. If anyone is surprised by power line exfiltration they just didn't do a basic google search.