RF Shielding NM-B - Mike Holt's Forum

Ok, I was told I am not including enough information.

• I am running 10/2 NM-B in residential homes.
• I am running each branch circuit to a dedicated receptacle from the panel.
• 120 volt circuits
• I am powering high end audio gear that is very sensitive to RF.
• Most instances there is a signal voltage of about 2mV that is being boosted either 40 to 60 times its original voltage. It is very sensitive to noise.
• I don't like MC cable/EMT due to the parallel path of the metal case which causes all sorts of ground issues. Yes I run an extra ground and use isolated ground receptacles. This is what we do in recording studios. Most of my clients are home owners. Not studios. They do not want to use a Hubbell receptacle. They are going to replace the receptacle with a boutique one. Non of those are isolated ground.
• I have clients asking to shield the entire room. I have to advise an RF 5ghz wave is about 7cm long. It can slip through small cracks. They would have to use paints on the inside and outside the building. Fabrics in the walls and ceilings, as well as floor. films on windows as well as curtains. And all that needs to attached to a robust ground system. Its a massive endeavor. I thought it might be easier to apply some of these treatments to the in wall cabling itself. When I exit the wall most power cables and interconnect are shielded.

What worries me the most is the shielding on the cable needs to be grounded to work. That means I have a 20 awg dead soft silver wire wrapped around the entire length too ensure the whole of the sheath will drain properly. I have experimented with this idea. I know it works. But I worry an inspector will say that drain is a conductor that is not inside the raceway. 300.3(B). But its not really a conductor. Its only terminated on one end. In the main panel. Its a bond for a Mylar or RF fabric.

Interesting I said Bond. I wonder if I would have to wrap it down with a wire that is 10AWG? Its not a raceway. But a Mylar and RF fabrics are conductive. It is technically something that could become energized?????

I have not started specifying this technique as it is somewhat unusual and I want to know if electrical inspectors have a valid reason to say I can not do as such. If they do, I wont do it. I always specify NEC/UL compliant installations. But my test in my shop show I can shunt a significant amount of noise by using Mylar/RF fabric with a drain and tech flex over the top to protect the sheath. These rf signals are being amplified from the power connection and not the signal input? Seems like they need more filtering in the amplifier power supply. What is the harm of RF? How can they hear it?

Ive built 3 shielded rooms and it is not easy (it is not my area of expertise, but i seemed to know more of the issues than anyone else so i was voluntold). I was trying to get 100dB of attenuation and it was more like 30. Used foil on the walls and ceiling. Floor was metal pan. The door is the bugger, especially if you want years of service.

All power and signal lines had rf filters at the foil perimeter. Even if you shield most of the branch circuit, how do you keep rf from coupling to it in the panel or from other cables you didnt shield that couple through the neutral bar or power bus.