TL;DR: If the cable entering the shielded room carries Ethernet, we have you covered. If it carries something else, we still probably have you covered. Four questions will make sure:
- What equipment is on each end of the cable?
- Is the device on the Ethernet network?
- What connector and cable are being used?
- Is power carried on the same cable?
Any one of them narrows the field; two usually land on the exact filter. The rest of this article explains why those four questions work.
Customers describe their filter requirements in very different ways.
| Customer says | What we still need to know |
|---|---|
| “I need a CAT 6 filter.” | What signal the CAT 6 is carrying. |
| “I need an RJ45 filter.” | What’s plugged into the other end. |
| “I need a filter for the camera.” | Network camera, or analog? |
They might all be talking about the identical signal requiring the same filter — or about three completely different signals that need three completely different filters. The name of the cable, the shape of the plug, and the job the device does are all clues. But only one thing determines the right filter: the signal traveling on the conductor as it enters the room.
Every wire that passes through the wall of a shielded room is called a conductive penetration, and every one of them needs a filter matched to the signal it carries. Not the cable. Not the connector. The signal.
The rest of this article walks through the clues in the order customers usually give them — what the device does, what the cable is, what the plug looks like — and ends at the answer: what the signal is.
What the Device Does — a clue, not an answer
The application — “it’s a camera,” “it’s the nurse call,” “it’s the fire alarm” — is usually the first thing anyone knows about a cable. Good information to have, but by itself it almost never identifies the filter. Most of these systems come in an older version that doesn’t use Ethernet and a newer version that does, and both versions often run on the same CAT cable with the same RJ45 plug.
| The device | What it could be | The tell |
|---|---|---|
| “The camera” | A modern network camera (Ethernet, often with power on the same cable) — or an older analog camera that has never heard of the internet. | Does it plug into a network switch? |
| “The nurse call” | A modern system where every room station is a network device — or an older one sending simple electrical signals to a central panel. | Network switch or control panel — follow the wire. |
| “The fire alarm” | Usually one genuine network connection for monitoring, while the detector loops and horn/strobe circuits are not Ethernet at all — even when wired with network-style cable. | Ask per cable, not per box. |
The application might narrow down the options, but not enough. The question that settles it is simple, and you don’t need to be technical to ask it.
Whatever cable the application uses, ask the customer’s installer or IT person if the other end connects to an Ethernet network switch. Yes means it’s Ethernet and we have the filter. No — or nobody knows — means we keep going. “What’s a network switch?” means we need to ask different people.
What the Cable Is — the medium, not the message
CAT cable is where most of the confusion lives, so here is the two-minute explanation. CAT cable — CAT 5e, CAT 6, CAT 6A, and so on — is simply eight copper wires, twisted into four pairs, inside one jacket. What makes one CATegory different from the next? Mostly precision. Higher categories twist the pairs more tightly (and twist each pair at a slightly different rate so the pairs don’t interfere with each other), use better copper and insulation, and are tested to stricter limits on signal loss and crosstalk. Tighter construction means the cable stays electrically “transparent” at higher frequencies, and that translates directly into speed.
| Category | Typical Ethernet capability | Worth knowing |
|---|---|---|
| CAT 5e | 1 Gb/s at the standard 100 m (328 ft) channel length | Also supports some 2.5/5 Gb/s applications, depending on the installed channel and equipment. |
| CAT 6 | 1 Gb/s to 100 m; 10 Gb/s on shorter channels | 10GBASE-T reach is installation-dependent — commonly about 121–180 ft, limited by alien crosstalk (noise from neighboring cables, not extraterrestrials). |
| CAT 6A | 10 Gb/s to 100 m | The usual choice for full-length 10GBASE-T channels. |
| “CAT 7” | — | Never recognized by the US cabling standards body (TIA). The international standards call similar cable “Class F,” so the cable exists — the US label doesn’t. |
| CAT 8 | 25/40 Gb/s over short channels | Built for short server-to-server links in data centers. Pulling CAT 8 to a camera is buying a race car to fetch the mail. |
Now the myth-buster: the CAT rating almost never changes the filter. A CAT 6 cable carrying gigabit Ethernet and a CAT 8 cable carrying gigabit Ethernet get exactly the same filter, because the filter responds to the signal, not the cable’s rating.
And here’s the bigger point: because CAT cable is cheap, everywhere, and easy to install, contractors use it for everything. Those eight wires routinely carry things that aren’t Ethernet — control signals, low-voltage power, simple on/off contacts, and about a hundred other things engineers invented because “we had spare pairs.” The cable can’t tell you what’s on it. It’s just the road; we need to know what’s driving on it.
One more thing you’ll encounter: shielded CAT cable, which adds a foil wrap around the pairs. It helps reject noise — but only if the shield is properly grounded at both ends, and a badly grounded shield can actually make things worse by acting as an antenna. Either way, a shielded cable is not a substitute for filtering the penetration. They solve different problems.
The cable is the road. The signal is the traffic. The CAT rating is the speed limit — it tells you the fastest thing the cable could carry, not what it actually carries. Don’t ask what the cable is rated for. Ask what’s on it.
What the Plug Looks Like — sometimes an answer, usually not
Connectors fall into three groups: the ones that settle the question, the ones that usually settle it, and RJ45.
| How much it tells you | Connector | The signal |
|---|---|---|
| Settles it | HDMI | HDMI video. Nothing else uses that plug — a rare moment of clarity in this industry. |
| 3-prong plug or IEC connector | AC power. The IEC connector is the one on the back of every computer and piece of rack equipment. | |
| F-connector / RG-style coax | An RF signal — the screw-on fitting on the back of every TV and cable box. | |
| Usually settles it | BNC | Almost always analog video or an RF signal. (Broadcast folks: yes, digital SDI video also rides BNC — another reason to confirm.) |
| XLR | Almost always audio. | |
| USB | Usually USB data — but plenty of USB cables carry nothing but charging power. Worth confirming, rarely a surprise. | |
| Settles nothing | RJ45 | Anything. Truly anything. Keep reading. |
RJ45: The Great Impostor
RJ45 deserves its own paragraph, because it has earned it. Technically it’s an “8 Position/8 Conductor” (8P8C) modular connector, but most people — including us — call it an RJ45. The “RJ” stands for Registered Jack, from the old Bell System catalog of standardized telephone connectors. The number is just the catalog entry; RJ45 is not thirty-four better than RJ11. Your old home phone plugged in with RJ11, a small six-position plug carrying one or two twisted pairs. RJ45 is its bigger sibling: a wider eight-position plug carrying all four pairs of a CAT cable. And that’s all the RJ45 standard defines — the plug and which wire lands on which contact. It puts no restrictions whatsoever on what travels through those contacts. We see RJ45 carrying Ethernet, Ethernet with power (PoE), serial control signals, dimming controls, simple contact closures, low-voltage DC power, and dozens of proprietary systems.
The plug tells you the shape of the connector, not what signal is on the cable. “I need an RJ45 filter” is like saying “I need tires.” Excellent. Tires for what? A bicycle? A forklift? A Corvette? One more question always gets us there.
What the Signal Is — the answer
The signal is what the filter sees. Once we know the signal, the filter picks itself.
Our filters come in two families, and the difference is worth thirty seconds. A passive filter (our Pasif line) is built from simple electrical components that let the intended signal pass straight through while blocking high-frequency noise — nothing is altered, the signal just travels through a cleaner path. An active filter (our ACTIV line) does something stronger: it stops the incoming signal completely at the wall and generates a brand-new, perfectly clean copy on the other side. Nothing passes through; the signal is rebuilt. That rebuild is what lets active filters achieve 100dB of shielding effectiveness across a wide frequency band, and it’s also why each active filter works only with the signal it was designed to rebuild. Fast digital signals with broad frequency content, like Ethernet, get active filters. Slower control signals, plain power, and older protocols get passive filters.
Here’s the map:
| Signal | Filter |
|---|---|
| Ethernet (gigabit) | ACTIV 10G (100dB) or Pasif 1G |
| Ethernet (10-gigabit) | ACTIV 10G (100dB) |
| Ethernet with power (PoE, up to 60W) | ACTIV POE (100dB) or Pasif 1G |
| Not Ethernet: control signals, serial data, low-voltage DC, contact closures | Pasif 1G with terminal block adapter |
That last row is the catch-all worth remembering. When the signal on a CAT cable turns out not to be Ethernet, the answer is usually the Pasif 1G with our terminal block adapter, which breaks the eight wires out to individual screw terminals so each one can be connected to its real job. One filter, one adapter, and most non-Ethernet signals on CAT cable are covered. (Each line handles up to 500mA at 57VDC or 40VAC, so you’ll want to know the voltage and current on each wire.)
We also make active USB and HDMI filters and a passive AC power filter — if your penetration carries one of those, ask us.
And whatever the signal, the physical pass-through is already solved: every filter mounts through the shield wall with our Universal Mounting System, which handles walls from 1/8 inch to over 11 inches thick.
Four Questions That Get You to the Right Filter
If you remember nothing else from this article, remember these:
- What equipment is connected on each end of the cable?
- Is the device on the Ethernet network? (The customer’s installer or IT person will know.)
- What connector and cable are being used?
- Is power being carried on the same cable?
You don’t need to answer all four. Any one of them narrows the field; two usually land on the exact filter. Three makes our applications engineers smile.
Frequently Asked Questions
Can CAT 6 cable carry something besides Ethernet?
Constantly. Access control, RS-485, door contacts, low-voltage power, and dozens of other signals ride on CAT cable because it’s cheap and already in the wall. The category name describes the cable’s capability, not its cargo.
Does an RJ45 connector mean the signal is Ethernet?
No. The connector is just eight contacts. Ethernet is the most common tenant, but fire alarm panels, proprietary controls, and serial links use the same plug.
Do I need a different filter for CAT 5e versus CAT 6?
Usually no. The filter is matched to the signal, not the cable category. The same ACTIV 10G handles Ethernet from 10 Mbps to 10 Gbps regardless of which category cable delivers it.
Can a filter pass PoE?
Yes, with the right filter. The ACTIV POE is built for powered Ethernet up to 60W. Standard data filters do not pass power, which is exactly why we ask whether power shares the cable.
Why doesn’t PoE damage devices that weren’t built for it?
Because Power over Ethernet is a negotiation, not a firehose. Before applying power, the sourcing equipment probes the line for a specific resistance signature and only energizes the pairs when it finds one. A device without that signature simply never receives power.
The filter doesn’t care what the cable is called.
It cares what signal is on it.
If the cable carries Ethernet, we have you covered. If it carries something else, we probably still do. And if you don’t know, tell us what you do know — even if all you know is “it’s blue and has an RJ45 on the end.” We’ve started with less. Contact our engineering team and we’ll work backward to the signal together.
Still Not Sure What’s on the Cable?
Send us what you know — photos of the cable and connectors, equipment model numbers, or drawings. We’ll work backward to the signal.