By Greg Worthman, Product Manager, Amphenol Broadband Solutions
The Internet of Things (IoT) has increased, exponentially, the number of connected devices in the average home. From an entertainment standpoint alone, consider multiple set-top boxes, music devices, etc. Add to this home security devices such as electronic locks and cameras, as well as increasingly popular home management systems, connected appliances, and more. Each of these devices is vulnerable to surges produced by electrical events. Such current can enter the home through any number of conductive routes, including CATV cables. Often, electrical surges are the result of events that occur during severe weather.
When contemplating protection approaches for the customer’s premises some things to consider are:
- Power Line Shorts due to Fallen Trees – protection should include prevention of up to 500VAC from using the CATV drop as a path to ground
- CPE Loss – protection should isolate the CATV from the ground return path for surges entering the home via the AC wiring
- Reverse AC Faults – if home AC wires are reversed, protection should prevent a short circuit to ground
- Lower Operational Costs – any preventative measure is more valuable if it can reduce truck rolls, eliminate damaged equipment, reduce risk and/or increase safety
Lightning flashes occur in all 50 states as well as across Canada. The density of cloud-to-ground flashes varies widely depending on locale. Florida ranks first over the last ten years with 20.8 flashes per square mile while the state of Washington ranks lowest with a mere 0.4 flashes. These cloud-to-ground lightning flashes were measured by the National Lightning Detection Network® (NLDN®), which is owned and operated by Vaisala, over the land area inside state borders. Clearly, CATV engineers in those areas of the country at the higher end of the flash density spectrum must plan for lightning surge protection. Still, those that build and manage networks in areas that only experience occasional strikes must still keep protection in mind as the damage from an event can be just as severe no matter what part of the country it occurs in.
Electrical strikes from storm activity range from just a few to 100,000 or more volts, establishing a potential for arc-over point ignition sources and related architectural fires. Obviously, protecting the premises from ingress of these strikes will protect sensitive electrical equipment, the structure itself and could, quite possibly even save lives.
Of course, lightning is but one of the sources of possibly damaging surges. Power lines that have not been properly installed and/or maintained present another threat that can cause dangerous conditions. These types of situations may occur in rural environments, but can also be found in the networks of larger providers as well. Safeguarding against the danger presented by power lines and similar threats must be a consideration in the planning and deployment of communications networks.
Considering that both CATV coaxial cable and AC power lines are exposed to the electrical charges caused by lightning, and that surge levels are unpredictable, isolators are a logical deterrent to protect against passing current into the subscriber premises. Isolators protect persons, property and provider equipment from harm or damage – while maintaining the service provider’s demanded RF performance level. Such protection plays a significant role in reducing customer premise equipment (CPE) replacement costs.
The best approach to protecting networks includes a variety of preventive measures throughout the cable plant, including bonding, grounding, powering and isolation hardware. When considering the customer’s premises, Isolators prevent CATV lines from passing current. The ideal isolator design embodies both an open circuit throughout low frequencies of DC to 60 Hz ensuring safety, while simultaneously providing a short circuit across the entire 5 – 1000 MHz CATV frequency range - ensuring RF screening effectiveness. Isolators can also prevent a short circuit to ground if home AC wires are reversed.
Fortunately, there is much research and best practices that have been embodied in the standards developed around surge protection over the years. Many telecom companies prefer the ANSI/IEEE C62.41 standard for “Recommended Practices on Surge Voltages in Low Voltage AC Power Circuits” which specifically identifies surge levels and establishes the surge protection parameters necessary to achieve the highest telecom equipment survivability. Such documents can be an excellent source of information and can help to identify the proper products to address surge protection.
Another valuable resource is the vendor community itself. When considering working with a vendor, ask yourself:
- Has the vendor incorporated the appropriate standards recommendations in its products?
- Do the products degrade with repetitive spikes?
- Has the vendor incorporated surge protection across its product line?
- Does the vendor incorporate a variety of protection techniques in its products, signifying a deeper understanding of surge protection?
The right vendor can be the best insurance against catastrophic failure associated with an energy spike in the network.