Copper Twisted Pair Ethernet vs Extreme EMI: Testing Performance and Packet Loss

Written by Don Schultz, trueCABLE Senior Technical Marketing Specialist, BICSI TECH, INSTC, INSTF, Fluke Networks Copper/Fiber CCTT Certified

A potential significant operational risk to your structured cabling system is invisible. This invisible threat can cause Ethernet cable packet loss, inability to establish reliable link speeds, and can cause all sorts of mayhem that will make the average IT person rip their hair out trying to run down what is wrong. Is it a ghost or gremlin? Perhaps, but likely the reason is quite pedestrian in nature. It has to do with electricity and the fields it throws off.

Of course I am talking about the part of the electromagnetic spectrum that you cannot see, which is electromagnetic energy that can cause interference. You have experienced interference before, most likely with radio transmissions (old style FM/AM and WiFi access points), and not even realized it. This energy can become strong enough to affect physical cable, too. The reason has to do with how copper twisted pair Category cable such as Cat6 and Cat6A is constructed--the use of metallic conductors to carry electrical (low voltage) signaling. Metal, as it turns out, tends to not behave well when subjected to strong EMI fields. Highly conductive metal like copper (which is the best metal for metallic communications cable) just makes it worse.

Given all of this, and the paranoia people may experience due to an invisible foe, just how much of a threat is EMI and RFI to your LAN cable? The answers might surprise you, and trueCABLE conducted cable EMI testing around this to help you understand what might be a real threat and what might not. trueCABLE did some mad scientist experiments using microwaves, magnets, hair dryers, and electrical circuits so you would not have to. We then used uber-advanced testing equipment to find out what the effects were.

What is EMI and Why Does It Matter for Ethernet?

To understand EMI (Electromagnetic Interference) it is necessary to understand what EMR (Electromagnetic Radiation) is. EMR is a self-propagating wave of energy that results from periodic oscillations of electric and magnetic fields, as a result of movement of charged particles such as electrons. Anything moving charged particles will have some degree of resultant EMI field. In your home, that is literally anything powered by electricity, including the AC electrical circuits supplying the energy needed to power up your home appliances. Even human beings generate an electromagnetic energy field, although it is very subtle.

EMI (Electromagnetic Interference) is the undesirable disruption caused by a source of EMR that negatively affects the “victim”. This relationship is often referred to as “the disturber” and “the disturbed”. Not all EMR will result in interference, as it greatly depends on the field strength “the disturbed” is exposed to. EM fields are all around us at all times, unless you live in a lead lined box with lead walls a foot thick, in which case you are protected from external sources of EMR but still subject to sources of EMR inside your lead protective box.

Common Sources of EMI:

• DC Motors (especially brush type)
• Power lines and transformers
• Consumer electronics
• Household appliances
• Bunched (bundled) power circuits
• Breaker boxes
• Arc welders
• Power strips
• High voltage lighting (studio lighting, street lights, etc.)
• Fluorescent light ballasts
• Industrial equipment
• Radio transmitters, etc.

How EMI disrupts Ethernet signals

EMI strong enough to overcome the built-in EMI/RFI protection of copper twisted pair Category cable such as Cat5e and Cat6 will induce unwanted electrical currents (called voltage induction) onto the metallic copper conductors. This is often called “noise”. The following issues may result:

• Packet loss
• Signal distortion
• Reduced throughput
• Failed links
• Intermittently operating links

Your LAN equipment will do what it can to compensate, but ultimately it may not be able to prevent a complete link failure.

DC Motor EMI Interfering with Copper Twisted Pair Cable Conductors
Image courtesy of Fluke Networks

Copper Ethernet Cable Types and EMI Resistance

Typical unshielded (U/UTP) copper twisted pair Category cable (aka Ethernet) shrugs off mild forms of EMI pretty well. The very design of the cable provides a degree of protection. Copper twisted pair cable uses the following strategies to not only operate, but provides adequate protection from EMI in most situations:

• Differential signaling
• Pitch twist rate
• Varying twist rates on adjacent pairs
• Copper conductor insulation thickness
• Outer cable jacket

External EMI Passing Through Twisted Pair Circuit
Image courtesy of Guralp

Differential signaling with twisted pairs uses the twist rate to maintain constant relative distance from the EMI source to ensure both conductors get equal or near equal EMI coupling. As the EMI coupling should be equal on both conductors, this would be subtracted out at the sending/receiving ends via your LAN equipment.

If this is not enough to avoid EMI, the next steps for EMI mitigation are separation distance and shielding from the source of EMI.

Distance is your friend, and you can find a great deal of recommendations around separation distances in Top 2 Things to Consider When Running Ethernet and Power Cable. That said, sometimes distance alone is not enough. You may need to use shielded cable. Some shielded cable is better than others for certain types of EMI resistance and ESD protection. Shielded cable comes in many different types, and you can learn a great deal more about that in Ethernet Cable Shielding Types.

Test Setup: How We Simulated “Extreme” EMI

trueCABLE was curious about the actual “on the ground” effects of EMI on copper twisted pair communications cable. Simply put, what really causes packet loss and to what degree? This turned into quite a fun exercise in experimentation and thinking of ways to cause trouble, which is quite fun! We also discovered quickly that there are many permutations and combinations that may or may not pose issues. The trueCABLE team had to settle on a single cable type and four different potential problems due to time constraints! We tried to be “extreme” about it as well!

The trueCABLE team discovered early on that using shielded cable mitigated the effects of any of the below experiments we conducted, so we opted to use unshielded cable to show you test results that were not…boring.

Here is what the trueCABLE team did:

• We bought a hair dryer, microwave oven (700W), a big magnetic parts holder dish, and a 50 foot three-prong extension cord you can find anywhere.
• The team then installed a 295 foot trueCABLE brand Cat6 Unshielded Riser permanent link in our testing center at Kansas City, MO to measure Cat6 EMI performance.
  • Note this cable was run from rack to rack, terminated to trueCABLE brand Cat6 unshielded punch down keystone jacks mounted into unshielded tool-less patch panels.
• We attached the extension cord using nylon ties directly to the Cat6 unshielded cable, every four feet. The attachment total was 30 feet.
• The extension cord was then plugged in (or disconnected) for various test scenarios.

When plugged in, the extension cord was serving as a 120VAC electrical circuit that we could use to “disturb” the copper twisted pair Cat6 cable. The idea was to simulate the worst case example of Cat6 unshielded cable running too close in parallel to ROMEX in a wall, or other pathway.

The testing device used to evaluate how much “disturbing” the Cat6 cable experienced was a netAlly LinkRunner® 10G. Why did trueCABLE pick this device and not a Fluke Versiv2 (DSX-8000) certification device? Simply put, the certification device takes a momentary snapshot of the link and certifies it against the TIA standard but does not allow for reliable “what if” scenarios that can environmentally develop. The LinkRunner permitted BERT (Bit Error Rate Testing) to send and receive data packets at various speeds for as long as needed while we conducted testing. This permitted the “what-if” tests we needed to accomplish.

If you are interested in the different kinds of testers out there, and what they do, may I suggest taking a look at Ethernet Cable Testers: Which Is Best for My Application?

The Results: Performance and Packet Loss Under EMI

That said, we still certified the link according to the TIA Cat6 Permanent Link +PoE test metrics and the link passed. Of course this was with the electrical cord unplugged. This was to ensure that we started off with a good link.

The video provides a far more detailed analysis and explanation of what we did, but here are some pictures of the testing taking place:

Test #1: Electrical cord plugged into 120VAC outlet, but no load placed on AC circuit

Test #2: Strong magnet (AC electrical cord unplugged)

Test #3: Microwave oven load (AC electrical cord plugged in, microwave cycled on/off)

At this point, we were really beginning to wonder if our tester was working correctly. If so, what would it take to generate some error packets!?

Test #4: Hair dryer (same test setup as microwave, hair dryer swapped in replacing the microwave oven)

Analysis: What the Data Shows

So what do these tests prove and is this indicative of real world situations? That is a tough question to answer as each install is different. We can only summarize our findings for this particular environment with these tests we performed. We can make some concrete conclusions, however:

• Oscillation of the magnetic field is what generates EMI significant enough to generate data packet errors
• The mere presence of a singular 120VAC circuit (no load on it and therefore no oscillation) in close proximity to your unshielded Cat6 cable will not cause issues
• Strong magnetics (such as those used to secure parts trays to metal surfaces) do not cause issues no matter how close they get to the unshielded cable
• Not all consumer appliances or devices will cause severe enough EMI to generate data errors on your cabling even if an oscillating load is placed on that 120VAC circuit
• The hair dryer (of all things) was the trouble causer?

In summary of the test results, there are a lot of permutations and situations that make tracking down what will cause issues and what will not cause issues pretty difficult.

How to Protect Your Network from EMI

As mentioned above, generally you will want to use unshielded copper twisted pair Ethernet and simply keep your distance from any strong EMI sources. Here are some very generalized tips:

• You may run various types of communications cable inside the same pathway without issues. So coaxial cable, Ethernet cable, and even low voltage fire alarm cable require no separation. For the electricians among you, that means Class 2 and Class 3 circuits can be run together.
• NEVER run communications cable in the same pathway as 120V or higher electrical wiring unless the pathway has a listed divider or permanent barrier to keep them separate. In electrician-speak that means no Class 1, power, electric light, or non-power limited fire alarm cables in the same pathway as Class 2 or Class 3 low voltage cables unless a listed divider or barrier is installed.
• In situations where a dedicated pathway is not used (like inside wall cavities), a minimum separation of 2 inches on parallel must be maintained from Class 1, power, electric light, or non-power limited fire alarm circuits when using unshielded communications cable. This requirement does not apply when the communications cable is shielded or if the communications cable is permanently separated from Class 1, lighting, or electrical cable by using firmly fixed rigid non-conductive conduit such as PVC or flexible tubing.
• You may run low voltage communications cable over AC wiring at a 90 degree angle without restriction, but you should not allow the wires to physically touch. This is known as “crossing at right angles''.

trueCABLE recommends an 8 inch separation minimum (when in parallel with electrical wiring) with unshielded twisted pair cable. This may be reduced to 2 inches in the same wall cavity when using properly bonded and grounded shielded cable. As a best practice, the communications circuit should be on the opposite side of the wall cavity from any power circuits.

In extreme cases, you will probably want to opt for fiber optical cable. Fiber optical cable is immune to EMI interference issues. This is especially true if you intend to deploy a LAN with application speeds at or above 10GBASE-T in areas where EMI may pose an issue.

Conclusion

This testing was fun and interesting. The team had quite a bit of fun doing “what-if” scenarios and bringing creativity to this endeavour. It is obvious that a great deal more testing needs to be done in order to generate some broader and more useful tips and data points. We would like to invite any readers to please make suggestions for any “disturber” sources so we can further experiment. Experimentation with separation distance in parallel is a future product. For example: Will that hair dryer cycling on/off still pose issues if the electrical cable and Cat6 cable are separated by 6”? How about 2”? We want to know, and we are sure you do too! With that, I will sign off and say…

HAPPY NETWORKING!!

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