RF Shielding NM-B

[Rex Hungerford]

Is there anything saying I can not take a piece of 10/2 NM-B, paint the jacket with RF shielding paint, pull a mylar shield over it, wrap a drain wire around the mylar, cover it all in tech flex. The drain would only connect to the line side panel. The load side would be in a plastic box and the drain would be taped over.

Or the same situation but the NM-B jacket is wrapped in a RF shielding fabric, no paint, no mylar, then a drain wrapped over the fabric, then tech flex and landed the same as above.

Thanks

 

[ActionDave]

You are holding back on too much necessary information. What is the application? What are the voltages involved?

All the rules in the NEC are mandatory or permissive. The NEC says you shall or shall not do blah, blah, blah, and anything other than that is allowed. Ultimately it's up to you and your own conscience what you do in any electrical install.

 

[suemarkp]

If you're going to all that effort, why not just use MC cable or sleeve the NM in FMC? Or how about an RF filter near the item which is either causing RF or being affected by RF? Are you trying to do a TEMPEST retrofit?

 

[tom baker]

Please Sweeny post in members trading post on the book about tracing emfs, it also discusses gaussmeters. The book is about to go to goodwill if you want it let me know

 

[hbiss]

Why don't you just run EMT and be done with it?

-Hal

 

[Jon456]

Is this for a homeowner who's paranoid about EMF radiation?

 

[Rex Hungerford]

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.

 

[suemarkp]

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.

 

[Rex Hungerford]

Filters on equipment can dramatically reduce dynamics and life. Puts a veil over the music.

RF acts much the same when coupled to the power line. It creates a distortion that blocks your ability to hear full frequency. I'm not saying that technically correct. You hear it when you get rid of it. Details you never heard in a record are there. A stand up bass or violin will sound more like its in the room with you. Not like its on a record.

There are some filters that block RF. On some systems they work well on preamps and digital equipment. That is one place were I have heard a back to back, filtered and not filtered. Its very apparent.

I have never heard a filter improve an amplifier. The amp always sound better direct to the wall. So I want to shield the power to those outlets for sure.

And yes you have a point, any break in the shield and noise can get back in. A plastic plate over the duplex could let it in. The duplex itself could let it in. It gets all over. My hope is to limit the expose by shielding as much as I can. All the in wall wires are antenna.

 

[ActionDave]

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.

What is a "dead soft silver wire"?

 

[Rex Hungerford]

What is a "dead soft silver wire"?

Pure silver wire. Comes in many gauges. I use 20 to 22 awg. Dead soft is just a term for how stiff it is. Some is medium soft. Harder to wrap and bend.

 

[ActionDave]

Pure silver wire. Comes in many gauges. I use 20 to 22 awg. Dead soft is just a term for how stiff it is. Some is medium soft. Harder to wrap and bend.

I've never heard of it. Sounds expensive. Where do you get it? Who is in charge of regulating the quality and purity of dead soft silver wire?

 

[Rex Hungerford]

I buy it through Rio Grand. A online jewelry shop. Its not signal wire. Its a drain. I could use copper too. Non of that is very pure eithet. The copper that is. Most is cheap china wire pulled through high speed dies with all sorts of crystal boundary. Real, pure copper cost $16 to $40 a foot for 10/2. But non is UL for use in the USA.

 

[don_resqcapt19]

Sounds like you need to install a technical power supply and shield the output side. No matter what you do to the branch circuits, there will be RF introduced on the line side of those branch circuits. However 647.3 does not permit them in dwelling units. I understand there are some cord and plug connected ones that can be used as long as everything is connected by cord and plug.

 

[ActionDave]

I buy it through Rio Grand. A online jewelry shop.

Never heard of them.

Its not signal wire. Its a drain. I could use copper too. Non of that is very pure eithet. The copper that is. Most is cheap china wire pulled through high speed dies with all sorts of crystal boundary. Real, pure copper cost $16 to $40 a foot for 10/2. But non is UL for use in the USA.

That china stuff is so inferior.

 

[Rex Hungerford]

Hopefully this can not get too sidetracked. I understand a lot of people get consternation over rich people going to crazy extremes with their hobbies. I am trying to assist them in getting the most from what they are doing. I think I touched on a important point in my additional comments. If I do this, am I actually bonding a metalic object that could become energized and 20 AWG would be to small. Would 250.96 apply. 250.102? Table 250.122?

 

[Russs57]

If you use a high quality amplifier and feed it with a perfect 60 hertz sine wave....you will get high quality power.

You might want to consider the distortions that the audio equipment causes.

I like "balanced power" myself. Anything remotely digital has an isolation transformer and a filter in front of it.

I like vinyl and tubes.

 

[Rex Hungerford]

Never heard of them.

That china stuff is so inferior.

As a total aside, can anyone help me get 10/2 NM-B that is twisted, with a jacket on the ground and made with better copper in the USA. I would purchase a 10,000 spool if I could get it for $1 a foot.

 

[tthh]

So, I assume you're running 10/2 to a regular 20A outlet? To keep the impedance as low as possible?

What about 10/2 MC cable? Isn't that providing some shielding due to the outer metal cover and it has a full size ground?

 

[Todd0x1]

So you're doing this fancy wiring, but what about RF shielding the utiliy's feeders to the structure and isolating it from the neighbors with its own transformer, etc?