(they are all off pigtails)
Adamlau
What wiring method was used for making up the pigtailed joint/s?
Example,
Wires twisted together then soldered and taped?
Cheap plastic wire connectors? Wires twisted together or wires just group butted under the wire connector?
Spring wire electrical connector, such as Scotchlok* brand?
Wires first twisted together then connector installed?
Wires grouped together, not twisted, and connector installed?
All can make a difference in wire contact line resistance.
What wiring method was used to make up the equipment grounding conductor?
Worst is the crimp only ground wire connector.
I have five unused receptacles in a dedicated 20A room circuit (I built the house and am a GC). Was considering removing them (they are all off pigtails) in an effort to reduce overall resistance through the circuit and placing brass cover plate over the openings.
Adamlau
Not sure you will gain any benefit by removing the unused receptacles.
As for using a brass blank plate instead of plastic or nylon, again I see no benefit.
If you were connecting your audio equipment to one of the unused receptacles then yes the receptacle cover plate can make a difference.
As for using a brass blank cover plate to control RFI/EMI, that might control air borne RFI IF the electrical branch circuit wiring is installed in metallic conduit and a metal box.
If the wiring in the walls is NM-B sheathed cable,(example Romex*), I see no benefit what so ever. And if the wall electrical box is made of plastic the conductive brass plate could do more harm than good.
If the electrical box is plastic by NEC code the brass plate would have to be connected to the equipment grounding conductor.