Hidden Ethernet Failures That Don’t Show Up in Speed Tests

 We rely on speed tests like a doctor relies on a thermometer. It is the first tool we grab when the internet feels "sick." You open a browser, click "Go," and watch the needle spin. If the number comes back high—say, 900 Mbps on a Gigabit connection—you sigh in relief. The internet is fine. The problem must be Zoom, or the game server, or just a glitch.

But here is the uncomfortable truth: A speed test is a very shallow diagnostic tool. It measures throughput (how much data can be pushed through the pipe in a short burst), but it completely ignores stability, latency, power delivery, and physical integrity.

It is entirely possible to have a cable that passes a Gigabit speed test with flying colors but still causes your security cameras to reboot, your VoIP calls to sound robotic, and your file transfers to corrupt.

These are "phantom" failures—issues that lurk beneath the surface of a simple bandwidth check. In this guide, we will uncover the hidden ways Ethernet networking cables can fail without ever slowing down your speed test, and how to identify these silent killers before they ruin your network.

The "Micro-Drop" Phenomenon: Packet Loss

A speed test is an average. It sends a large file for about 10 to 15 seconds and calculates the average transfer rate. If your connection drops for 0.5 seconds during that test, the final number might dip slightly (from 950 Mbps to 920 Mbps), but you won't notice it. You still see a "fast" result.

However, in the real world, that 0.5-second drop is catastrophic.

• For a gamer: It’s a "lag spike" that gets you killed.
• For a VoIP call: It’s a robotic stutter or a dropped call.
• For a database: It’s a corrupted entry.

This is often caused by Packet Loss. This happens when a cable is damaged, kinked, or poorly terminated. The copper connection is physically unstable, causing data packets to "fall off" the wire. The router simply resends them (TCP/IP protocol), which maintains the illusion of a connection, but the real-time performance is destroyed.

To fix this, you need to ensure your infrastructure is built on high-quality Cat6 Plenum cabling that maintains tight twists and structural integrity, preventing the physical faults that lead to lost packets.

The Power Problem: Voltage Drops in PoE

Modern networks do more than move data; they move electricity. Power over Ethernet (PoE) powers security cameras, wireless access points, and door controllers.

A standard speed test only checks the data pairs (wires 1, 2, 3, and 6). It does not check the power delivery.

You can have a cable that transmits data perfectly fine at 1000 Mbps, but fails to power a camera at night. This usually happens when using cheap cabling with high resistance (like Copper Clad Aluminum). As the camera draws more power (for example, when the infrared night vision turns on), the resistance in the wire causes the voltage to drop.

• The Result: The camera reboots randomly.
• The Speed Test: Still shows 1000 Mbps.

To prevent PoE failures, you must use cat6 plenum cables made from 100% Solid Bare Copper. Copper has low resistance, ensuring that the voltage at the end of the run is stable, keeping your devices online regardless of their power load.

The Noise Floor: Crosstalk and EMI

Ethernet cables run through walls filled with electrical wires, and across ceilings filled with fluorescent lights and HVAC motors. All of these generate Electromagnetic Interference (EMI).

A speed test is a "loud" signal. It blasts data at full volume. Often, this blast is strong enough to overpower background noise, giving you a good result.

But normal network traffic isn't always a blast. It’s often a steady stream of smaller "handshakes" between devices. If your cable has poor shielding or loose twists, EMI can corrupt these delicate signals. This forces your computer to stop and ask for data to be repeated.

• The Symptom: Your mouse feels "floaty" in remote desktop sessions, or web pages hang for a second before loading.

In environments with high interference, standard unshielded cable isn't enough. Upgrading to Cat6A Plenum Cable provides a robust defense. Cat6a is designed for 500 MHz frequencies and often includes shielding (F/UTP) that acts as a barrier, reflecting noise away from the data and lowering the "noise floor" of your network.

The Vertical Stretch: Structural Deformation

Gravity is a silent enemy of network cabling. In multi-story buildings, cables run vertically through shafts (risers).

If a cable isn't supported correctly, its own weight can stretch the copper conductors inside the jacket. This stretching alters the "pitch" (the distance between twists) of the pairs.

• The Hidden Failure: The cable passes a continuity test (the wires are still connected), but the Impedance has changed. This causes "Return Loss," where signals bounce back down the wire.

A speed test might not catch this because the router compensates for the error, but the efficiency of the link is compromised. Using proper cat 6 riser cable is essential. Riser cables are engineered with distinct tensile strength properties to withstand vertical runs without deforming internally.

The Water Torture: Environmental Corrosion

Water is the ultimate destroyer of electronics, but it works slowly.

If you run a standard indoor Ethernet cable outside to a security camera, it might work perfectly for six months. A speed test will show full Gigabit speeds.

But microscopically, UV rays are cracking the jacket. Humidity is seeping in. Water travels via "capillary action" down the inside of the wire, eventually reaching the pins in your switch. As the copper oxidizes (rusts), the resistance rises.

• The Failure: One day, the link simply dies. Or worse, the water shorts out your expensive switch.

This is a failure of specification, not speed. Any cable running outdoors must be direct-burial. These cables feature a UV-resistant jacket and a gel-filled or tape-wrapped core that blocks water ingress, ensuring the cable lasts for years rather than months.

The "Good Enough" Termination

The connection point—the RJ45 plug or the Keystone jack—is the weakest link in any network.

A technician might crimp a connector where only 7 of the 8 pins make good contact.

• 10/100 Mode: Ethernet is smart. If it detects a broken wire, it often "downshifts" from 1000 Mbps (Gigabit) to 100 Mbps (Fast Ethernet) because 100 Mbps only requires 4 wires.
• The Trap: Your internet connection might only be 100 Mbps, so a speed test shows "Full Speed." You don't realize your internal network has been crippled by 90% until you try to transfer a file between computers.

Using high-quality ethernet cable accessories ensures a gas-tight connection on all 8 pins. Gold-plated contacts prevent corrosion over time, ensuring that your network negotiates at the highest possible speed every time you plug it in.

Installation Stress: Kinks and Snags

In large commercial installations, installers pull thousands of feet of cable. If a cable is pulled too hard (exceeding 25 lbs of tension) or yanked around a sharp corner, the copper inside can micro-fracture.

This creates a "high resistance event" at that specific spot. Data can jump the gap, but heat builds up. Over time, this weak point degrades.

• The Consequence: Intermittent connectivity that gets worse as the building warms up during the day.

Professional installers use spools designed for easy deployment, like a Black Cat6a Plenum on a wooden drum, to ensure the cable comes off smoothly without snagging. Careful handling during installation prevents these latent defects that no software test can see.

Regulatory "Failures"

Finally, there is a failure that has nothing to do with data: Safety.

A cable can transmit data at 10Gbps perfectly but still be a liability. If you use non-rated cable in a plenum air-handling space (the space above a drop ceiling), you are violating building codes. If a fire inspector sees it, you will be fined and forced to rip it out.

This is a financial and legal failure. To avoid this, always check the jacket rating. Using a CAT6 Plenum TAA Compliant ETL/UL Listed Cable proves that the cable has been tested for smoke and fire safety. The "ETL/UL Listed" mark is your protection against liability.

When to Look Beyond Copper

Sometimes, the hidden failure is simply asking copper to do something it can't physically do. Copper has a distance limit of 100 meters (328 ft).

If you run a cable 350 feet, you might get a link light. You might even get a ping. But the packet loss will be massive because the electrical signal is too weak.

• The Fix: Don't extend copper beyond its limit. For long-distance runs (campus backbones, large warehouses), switch to fiber optic cable. Fiber uses light, which can travel for kilometers without the signal degradation that plagues copper.

Beyond the Speed Test

A speed test is just a snapshot of your network's best-case scenario. It doesn't tell you if your network is safe, stable, or reliable.

Real network performance is about consistency. It’s about PoE cameras that stay on during a storm, VoIP calls that sound like you’re in the same room, and file transfers that never fail.

To achieve this, you have to look past the numbers and focus on the physical infrastructure. By choosing high-quality, solid copper cabling and the right jacket for the environment—whether it's Plenum for safety or Direct Burial for durability—you eliminate the hidden failures that software can't see. Build your network with NewYork Cables, and you won't just pass the speed test; you'll survive the real world.