A camera feed looks clean on the bench, then turns noisy after it's routed across a machine line. An RF link works during startup, then starts dropping packets when a VFD cabinet next to it ramps up. A maintenance tech swaps the sensor head, replaces the connector, checks the power supply, and the fault still comes back.
A lot of those problems trace to one quiet decision made early: the wrong coax cable. Not a defective cable. The wrong size, impedance, shield, connector fit, or jacket for the job.
In industrial work, coaxial cable sizes aren't just catalog details. They affect whether the cable fits the conduit, whether the connector grips the jacket correctly, whether the run survives repeated door movement, and whether the signal arrives with enough margin after it crosses a noisy plant floor.
What Do Coaxial Cable Sizes Really Mean
When people say “coax size,” they usually mean one thing and accidentally ignore three others.
They notice the cable looks thin or thick. What matters in practice is a combination of outside diameter, internal geometry, impedance family, and mechanical behavior. If you only look at the RG label, you can still make a bad choice.
The modern coax form goes back to a 1929 patent milestone documented by the National MagLab, filed by Lloyd Espenschied and Herman Affel and granted in 1931. That design formalized the familiar structure of a center conductor, insulation, and outer shield sharing the same axis. That basic arrangement is still what you're buying today, even when the part numbers and jacket materials change.
In a plant, that geometry becomes practical fast. A smaller cable may route cleanly through a hinge area or crowded enclosure. A larger cable may handle a longer RF or video run with less trouble. Neither one is automatically “better.”
Practical rule: Coaxial cable sizes describe both the cable's physical envelope and the electrical system it belongs to.
Size is more than diameter
Two cables can look close in thickness and still belong to different use cases. One may suit a short jumper to an antenna coupler. Another may be more at home on analog video or a longer backbone run. If the impedance is wrong, the connector is wrong, or the bend radius is ignored, the installation may still fail even if the cable physically fits.
That's why broad application context matters. If you need a refresher on where coax shows up across RF, video, communications, and equipment interconnects, this overview of what coaxial cable is used for is a useful baseline.
What engineers should check first
Before comparing part numbers, ask these questions:
- What signal are you carrying. Analog video, RF, antenna feed, test signal, or another coax-based link.
- How far is the run. The route on paper is rarely the route in the machine.
- What's the environment. Oil mist, abrasion, washdown, heat, vibration, and EMI all matter.
- How will it terminate. A good cable with the wrong connector family becomes scrap.
If you treat coaxial cable sizes as just a thickness choice, you'll spend time chasing faults downstream.
Anatomy of a Coaxial Cable and Its Core Components
A coax cable is easiest to understand if you think of it as a protected pipeline. The signal travels in the center path. The surrounding layers keep that path stable and defend it from outside noise.
The center conductor and dielectric
The center conductor carries the signal. In practical terms, this is the path you're trying to preserve from one end of the run to the other. If that conductor gets nicked during stripping or work-hardens from repeated flexing, performance can drift long before the cable looks obviously damaged.
Around it sits the dielectric insulator. This layer doesn't just prevent a short to the shield. It holds the spacing between the center conductor and the outer conductor. That spacing is a big part of what establishes the cable's characteristic impedance.
Consider the spacing inside a precision bearing. If the dimensions shift, the assembly still exists, but it no longer behaves the way it was designed to.
The shield and outer jacket
The shield is the cable's protective barrier against external electrical noise. In a factory, that matters around drives, motors, switching supplies, welders, and long parallel runs with power conductors. The shield also serves as part of the coax transmission structure, so poor termination at the shield side isn't a cosmetic defect. It directly affects performance.
The outer jacket is the mechanical armor. It's what takes the scraping, clamping, oil exposure, and general abuse of routing through trays, machine frames, and enclosure entries. A cable can have the right electrical design and still fail early if the jacket doesn't match the environment.
A coax cable works because its geometry stays controlled. Once installers crush it, over-bend it, or terminate it with the wrong tooling, the cable may still pass continuity and still perform badly.
Why geometry matters
Coax isn't just “wire with shielding.” It's a controlled transmission line. Major reference guidance notes that the most common coax impedances are 50, 75, and 95 ohms, with specialized applications ranging from 35 to 185 ohms according to ShowMeCables' coax history summary.
That's why connector selection has to match more than just thread style or coupling style. The cable's OD, dielectric dimensions, and impedance family all need to line up with the connector and tool set.
A quick layer-by-layer check
When I inspect a field termination, I'm looking for four things:
- Center conductor condition. No scoring, bending, or partial cuts.
- Dielectric shape. No mushrooming, crush marks, or heat damage.
- Shield preparation. Braid and foil handled cleanly, with no stray strands bridging where they shouldn't.
- Jacket support. The connector body should grip the jacket correctly, not just the braid.
If one of those is wrong, the assembly may work for a while. That's the dangerous kind of failure.
Common Coaxial Cable Types and Specifications
The RG label helps you narrow the family, but it doesn't replace reading the actual cable spec sheet. In industrial environments, I treat RG as a starting point, not a final answer.
The reason is simple. Coaxial cable sizes act as a shorthand for both electrical class and mechanical envelope. Widely used families span about 4.95 mm OD for RG-58, 6.15 mm for RG-59 and RG-62, 6.90 mm for RG-6, and 10.30 mm for RG-11 and RG-213, as outlined in the RS coaxial cable guide. That spread changes how the cable bends, what gland or bulkhead it fits, and which connector bodies terminate properly.
The common families in plant work
Here's the practical view.
RG-58 is one of the smaller common options. It's easier to route in tighter assemblies and short equipment runs. I usually think of it as the cable you choose when routing flexibility and compactness matter, and the run length isn't pushing the design.
RG-59 often shows up in video-oriented conversations and legacy-style camera work. It sits in a middle zone mechanically, where installation is still manageable but the cable feels more substantial than RG-58.
RG-6 is a common workhorse when a project needs a broadly familiar cable family with more physical body than the smaller options. It often lands in video and RF-adjacent installations where a technician wants a practical balance between routing and lower-loss behavior.
RG-11 moves into the larger, stiffer category. With this, installers gain electrical advantage on longer runs but start paying for it with bend radius, termination bulk, and cabinet-entry headaches.
Common Coaxial Cable Specifications
| Cable Type | Impedance (Ohms) | Outer Diameter (Approx.) | Center Conductor | Common Industrial Use Case |
|---|---|---|---|---|
| RG-58 | Commonly used in 50-ohm systems | 4.95 mm | Varies by construction | Short RF jumpers, tighter routing inside equipment |
| RG-59 | Commonly used in 75-ohm systems | 6.15 mm | Varies by construction | Analog video and shorter CCTV-style runs |
| RG-6 | Commonly used in 75-ohm systems | 6.90 mm | Varies by construction | CCTV, video distribution, general longer in-building runs |
| RG-11 | Commonly used in 75-ohm systems | 10.30 mm | Varies by construction | Longer backbone-style runs where lower loss matters |
I'm leaving the center conductor entry qualitative on purpose. Manufacturers vary the conductor material and construction, and it is at this point that people get into trouble by assuming all cables with the same RG label are identical.
What works and what doesn't
What works is matching the cable family to the actual installation.
- RG-58 works well when you need compact routing and the signal path is short enough that a smaller cable won't become the weak point.
- RG-59 still fits older video and shorter surveillance-style runs where flexibility matters more than squeezing every bit of attenuation margin.
- RG-6 is often the compromise when a team wants a familiar size that supports broader use without the stiffness penalty of larger cable.
- RG-11 earns its place on longer routes where the run length justifies a bigger cable and larger connector hardware.
What doesn't work is selecting by habit. I've seen technicians choose the cable they keep on the truck, then fight gland fit, connector mismatch, and awkward cabinet bends for the rest of the day.
If you need a cable to turn sharply inside a machine door, a larger coax may solve one electrical problem and create three mechanical ones.
Don't trust the RG number alone
Always confirm these details on the actual part:
- Impedance
- Outside diameter
- Shield construction
- Jacket rating
- Connector compatibility
That last point gets overlooked most often. A connector sold for “RG-6” may still not fit every RG-6 cable correctly if the braid, dielectric, or jacket dimensions differ enough from the connector's expected geometry.
How Cable Size Impacts Signal Loss and Frequency
Cable size affects signal loss the same way pipe size affects flow. A larger path usually lets you move what you need with less penalty over distance. In coax, that penalty shows up as attenuation.
For practical field work, the two big rules are straightforward. Longer runs lose more signal, and higher-frequency signals are less forgiving than lower-frequency ones. That's why a cable that seems acceptable for one low-demand link can become troublesome on video, RF distribution, or higher-frequency test work.
Why larger cable often helps
A larger cable generally gives the signal an easier trip. That doesn't mean every large cable is ideal, but it does mean diameter often buys you useful margin on long runs.
This visual makes the trend clear.
The chart compares RG-6 and RG-11 and shows lower loss for the larger cable across the same frequencies. That lines up with what installers see in the field. If the route is long and the signal budget is tight, upsizing the cable can be the difference between a dependable installation and one that only works when conditions are perfect.
Why bigger isn't always better
The mistake is assuming lower loss automatically means best choice.
A larger coax is harder to bend, harder to dress cleanly inside compact enclosures, and less pleasant to terminate in volume. On moving equipment or in cramped machine frames, those mechanical penalties can outweigh the electrical gain.
There's also an impedance trade-off underneath the size discussion. The Wikipedia coaxial cable reference notes that historically optimal impedance for lowest loss in air dielectric is about 76.7 Ω, while more common dielectrics shift the low-loss range to 52–64 Ω. Maximum power handling is instead near 30 Ω. That's why industry settled around practical standards like 50 ohms and 75 ohms. They represent engineering compromises, not magic numbers.
Field judgment: The best cable is the one that meets the signal requirement and still survives the route, the bend, and the connector scheme.
What frequency changes in real installations
As frequency rises, installation quality matters more. Small geometry changes that might be tolerated at lower frequencies can become expensive mistakes.
Pay attention to these failure points:
- Tight bends. These distort the cable geometry and can change local impedance.
- Poor shield termination. Noise rejection suffers, and the transmission path itself is compromised.
- Wrong connector match. Even if it “fits,” the transition may be poor enough to create reflections or excess loss.
- Unnecessary adapters. Every added interface is another opportunity for mismatch and mechanical looseness.
If you're designing for reliability, don't treat coax like generic hookup wire. At higher frequencies, it behaves more like a precision mechanical part with electrical consequences.
Choosing the Right Coax for Industrial Automation
In industrial automation, choosing coax is rarely about the prettiest spec sheet. It's about surviving the operational route and preserving enough signal margin that maintenance won't inherit a recurring fault.
I use a simple selection process. Start with the signal, then the route, then the environment, then the connector system. If you reverse that order, you usually end up forcing the wrong cable into the project because the connector was convenient or the stockroom had a partial reel left.
Start with the signal and run
First, define what the cable is carrying. A short RF jumper inside a panel, a plant-floor camera run, and an antenna feed to a roof-mounted device don't place the same demands on the cable.
Then map the actual route, not the straight-line distance. Include tray drops, service loops, door movement, bulkhead transitions, and detours around hot or noisy equipment.
A practical decision path looks like this:
- Identify the system impedance. If the equipment expects 50 ohms, don't try to “make” a 75-ohm cable work because the connector body looks similar.
- Estimate how demanding the run is. Long routes and higher-frequency signals generally justify a larger cable family if the mechanics allow it.
- Check routing difficulty early. If the cable must pass through a tight hinge area or crowded gland plate, a physically smaller cable may be the only workable choice.
- Choose margin on purpose. If the installation is hard to access later, don't design on the edge.
Match the cable to the environment
Plant conditions punish weak assumptions.
A coax route near drives and motor feeders needs strong shielding discipline and careful separation practice. A washdown area needs jacket and sealing details that won't turn brittle or leak. Outdoor runs need weather-aware entry points and strain relief.
That same thinking applies when the project lives in a modified enclosure or containerized equipment package. If you're planning cable routes through retrofitted structures, this Quickfit Container Accessories guide is useful for thinking through penetrations, mounting changes, and physical layout before you finalize cable entries.
Connector fit decides whether the design is real
The cable OD often proves to be the downfall of many decent designs. It isn't a footnote. It dictates whether the connector, gland, clamp, and bulkhead hardware will support the assembly correctly.
For industrial builds, I check these items together:
- Connector family. BNC, TNC, N-type, and other styles all bring different mechanical and environmental trade-offs.
- Cable-specific termination parts. The connector must match the cable's actual geometry, not just the rough RG name.
- Panel and enclosure hardware. Entry hardware has to fit the jacket OD and hold strain without crushing the cable.
- Serviceability. A beautifully compact termination that can't be reworked on the plant floor is often the wrong answer.
If you're reviewing the wider connector range around machine and panel work, this guide to industrial automation connectors helps frame how coax interfaces fit alongside the rest of an automation system.
Good coax selection happens where electrical performance and installability overlap. If either side gets ignored, reliability drops.
What I'd choose in common plant scenarios
For a short internal RF link, I'd lean toward a smaller cable that routes cleanly and doesn't fight the enclosure layout.
For a camera run across a facility, I'd pay more attention to route length, EMI exposure, and how many transitions or adapters the run includes.
For a longer backbone-style link, I'd strongly consider a larger cable if the tray space, bend radius, and connector hardware support it.
For a high-vibration machine, I'd favor the cable and connector combination that holds geometry and strain relief well under motion, even if that means giving up some convenience during installation.
That's the fundamental balancing act behind coaxial cable sizes in automation. The cable has to perform electrically, fit mechanically, and stay stable after the machine starts doing its job.
Installation Tips for Reliable Coaxial Connections
A well-chosen cable can still fail because of bad installation. Most coax problems I see in service work come from termination damage, crushed routing, or poor support at the enclosure entry.
Handle the cable like a controlled part
Don't strip coax with whatever side cutters happen to be in the pouch. Use the stripping tool made for that cable family and connector style. The difference shows up immediately in dielectric condition and braid control.
Respect bend radius. If an installer forces a large coax around a sharp cabinet corner, the cable may pass a quick continuity check and still perform poorly. Coax depends on geometry, so crushed or ovalized sections matter.
A few habits prevent most field failures:
- Use the correct prep tool. Clean, repeatable strip lengths matter on coax more than on ordinary power wire.
- Support the cable near entries. Let the connector carry signal, not mechanical load.
- Seal outdoor or wet-area terminations. Water intrusion usually starts at the connector transition.
- Keep the shield intact. Sloppy braid handling creates intermittent problems that are hard to diagnose.
Pay attention to entries and strain relief
Cable entries deserve more thought than they usually get. If the gland or bulkhead insert doesn't fit the cable OD correctly, the assembly either slips, leaks, or gets over-compressed. A solid reference on selecting the right sealing hardware is this guide to cable glands.
I'd also treat coax runs the same way I treat structured cabling work in offices and technical spaces. The root causes overlap more than people think: poor terminations, bad routing discipline, and unnecessary stress on the cable. This article on addressing slow office internet issues is useful because it reinforces the same installation mindset, even though the application context differs.
Don't judge a coax termination by appearance alone. Tug retention, shield continuity, and fit at the jacket are what keep the link stable over time.
A simple verification routine
Before closing the panel or handing the machine off, I'd check:
- Connector seating. Fully engaged, mechanically secure, no wobble.
- Jacket support. The connector or strain relief grips the cable properly.
- Routing quality. No flattening, kinks, or sharp edge contact.
- Shield path. No loose strands, no accidental shorts, no exposed mess.
- Environmental protection. Outdoor or washdown connections sealed and supported.
If you want a visual walkthrough of basic coax handling and termination, this short video is a useful companion.
A reliable coax install usually looks uneventful. That's the point. No heroic troubleshooting later, no mystery noise, no intermittent alarms after the first production shift.
Products for Automation carries a broad range of industrial connectivity components, including cable management and interface hardware that help engineers build cleaner, more reliable systems. If you're sourcing parts for a machine build, retrofit, or maintenance job, visit Products for Automation to find compatible industrial components with clear specifications and support.