Are You Leaving the Back Door Open?

Unshielded twisted pair cable is a great way to transmit audio and video signals for long distances around homes, offices, churches and restaurants. Audio Authority has used UTP cable and balanced line technology for years because it inherently rejects RF interference. While every professional integrator installs AC power conditioners and surge protectors on AC lines, many do not realize that UTP cable presents a potential back door for transients to damage expensive equipment. Transients, or transient spikes, are brief but powerful surges, sometimes exceeding 100,000 volts. This article explores the exposure and the remedy that UTP cable presents to AV integrators.

Myth #1: All Significant Power Surges are Caused by Lightning or Downed Power Lines

The most powerful transients are usually caused by lightning or the occasional suicidal squirrel, but many damaging transient spikes originate from utility grid switching or even internal sources such as load switching or loose connections. In fact, 80% of transient spikes originate inside the building!  When an electric motor starts, lights are switched on, or any other power switch is closed, the electrical circuit is briefly disturbed by a spike in voltage and current, potentially causing damage to connected equipment. Examples include refrigerators, air conditioners, copy machines, banks of fluorescent lights, and any equipment that has motors that switch on and off.

Myth #2: AC Surge Protectors Protect All Equipment Down Stream

Why aren’t surge protectors on the AC line able to protect equipment connected by UTP cables? Each AC circuit produces a field, and if UTP cable is near enough, noise in that field can be induced into the UTP cable, potentially causing damage to the equipment at each end. Long runs of unprotected UTP cable act like antennas, so when a UTP cable is routed near an AC line, a strong transient can cause catastrophic damage, even though surge protection breaks the path to the AC circuit.

Myth #3: Minor Transients are Not Dangerous

External sources generally cause the immediate, catastrophic damage, but smaller transients can cause damage over time. UTP cables carrying audio and video signals are connected to equipment with sensitive components. Microscopic runs on processor chips are extremely susceptible to transient related heat stress. The first transient may just cause a heat blister on a tiny trace, but repeated small transient spikes encounter the resistance of that blister and can eventually interrupt the trace, causing a failure. Failures like this are generally attributed to normal wear and tear since they can’t be attributed to a major transient event.


While every electrical environment has transients, equipment damage is not inevitable. Ideally, UTP cable should be kept away from AC lines, but this is not always feasible. AV integrators should install surge suppression for long UTP cable runs, and not just in lightning-prone regions. There are frequent surges produced inside every building that could be doing cumulative damage to high-value equipment. Install UTP surge protectors designed for use with audio and video signals to protect your customers’ custom electronics investment.