Disclaimer: I'm not a trained electrical engineer...I'm a recent Computer Science grad with about ten years experience as a RF test tech. I don't know everything, and to me, experience reigns supreme for practical applications like this. I'm also the only RF person in my organization. I'm reaching out for an experienced RF, EMI, or EMC specialist to chime in on this issue.
I have a wireless shielded room which doubles as an office constructed of 16 gauge welded steel used for isolating emissions within it from the outside world. It hasn't been maintained well and there have been several improper electrical penetrations of the shield in the last couple of decades. As the new RF engineer, I'm trying to restore the shielded effectiveness (SE) for electrical field and plane wave attenuation of at least 60dBm up to 10GHz. We'll have an SE test done after the repairs are complete.
I've made several repairs, including designing and installing waveguide-below-cutoff (WBC) penetrations for fiber and getting rid of ethernet and coax cables. I've properly filtered all of the POTS phone lines, made some repairs to the finger stock & knife edge doors, patched holes, checked the honeycomb filters, and treated several areas for corrosion/rust.
Here's the last remaining issue...
The room has digital control lines for HVAC thermostats (Metasys N2, RS485, shielded twisted pair) going through the "dirty side" of the filter enclosures and penetrating through a small 3/8" hole in 16 gauge steel to the "clean side" of the filter enclosure. I'm not allowed to remove the lines. I have two options that I can see: convert to fiber and pass through a WBC or bond the cable shield to the steel enclosure. Electrically filtering the digital cables, from what I think I understand, would be problematic because it would filter out the high-frequency components in the digital signals. Please correct me if I'm wrong there. Converting to fiber is difficult due to a lack of AC outlets for the fiber converters on both sides of the shielded room.
I think I want to bond the cable shield to the steel enclosure and stuff the 3/8" hole around the cable with steel or copper wool. Do you experienced folks think that this will be "good enough" to achieve the shielded effectiveness of >60dBm for electrical field and plane wave attenuation up to 10GHz?