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 ~ National Lightning Safety Institute ~

Section 5.1.11

Going Beyond the Codes: An Expanding List of On-the-Job Tips

By Richard Kithil, President & CEO, NLSI

General Safety

  1. Don’t work on any lightning protection issues where thunderstorms are forecast.
  2. When working around RF, wear a personal electromagnetic energy (EME) monitoring device.
  3. Always have some form of two-way communications while working alone.

Electromagnetic Energy Safety

  1. In environments where explosion hazards may exist, non-incendive intrinsically safe electrical components must be used where acceptable. Note that some areas may be entirely unacceptable for housing electronic equipment.

Communications Sites

  1. Aluminum ladders designed for climbing should not be used as cable trays or runways.
  2. Cable separation should consider AC power, DC power, RF, ground, and data ground cables to avoid induced interference.
  3. Leave all battery issues to a battery expert.
  4. Fixed or portable fire suppression systems must not be used in communications sites. If a building has a sprinkler system, make sure the cable runways do not block the sprinklers.
  5. Generators installed outside buildings, within 1.8m (6 feet) of the buildings, must be bonded to the nearest practical earth electrode system. Longer distances should have an additional ground rod.
  6. Generators inside buildings should have fresh air intake sized at 1.5 times the radiator dimensions to assure adequate ventilation. Vibration isolation between the generator and frame is recommended.
  7. For tower-top pre-amps that require DC voltage for operation, use a lightning arrestor that can pass DC current.
  8. To pass a safety inspection, must-have items include ABC and CO2 fire extinguishers; first aid kit; interior and exterior lighting.
  9. Incoming coaxials must be run through weather ports (boots) that also are rodent- and insect-proof.
  10. Tower lighting cables carrying AC power should not be bundled along with transmission lines or other conductors anywhere within cable ladders or the building interior.

External Grounding

  1. Before excavating or digging, do the “locates.” Call before you dig!
  2. Exothemic welding should not be done unless another person (experienced in first aid) is present. A suitable fire extinguisher should be present during the process.
  3. Wear safety glasses, hard hat, and steel-toed boots when working with high-compression fittings.
  4. Braided bonding straps should not be used because they corrode too quickly and can be a point for RF interference.
  5. Avoid differences in potential. Do not install separate grounding electrode systems. Follow NEC 250/IEEE 142/FAA 019d requirements here.
  6. Before disconnecting a grounding electrode conductor, check for current. Never disconnect the ground of a live circuit — death or severe injury could result.
  7. For non-critical sites, an electrode system resistance of 25 ohms is OK. For critical sites, where disruption of service could cause system-wide outages, an electrode system resistance of 5 ohms is suggested. “Outside the box” solutions to improving grounds include chemical ground rods; prefabricated/buried wire grid; Ufer ground; magnesium sulphate; and other backfills. (The best cost/benefit artificial ground enhancement electrode is Coke Breeze. Avoid bentonite due to its shrinking and expanding properties.)
  8. Check soils for pH (hydrogen ion concentration) for acidic soils where pH is below 7. In highly acidic soils, larger diameter conductors should be considered.
  9. Optimum spacing apart for ground rods is 2 X length.
  10. A bare copper buried ring electrode provides more conductor surface area than many rods. Consider a ring electrode where practical.

Power Sources

  1. Aluminum conductors should not be used. Never mix aluminum and copper wires, connectors, panels, or receptacles. The two metals have different coefficients of expansion, so loose connections or joints can result.
  2. Consumer grade power receptacle strips should not be used for permanent installations. Do not mount receptacle power strips on the floor. Damage can result from foot traffic, water, water seepage, or fire sprinkler activation, with electrocution of personnel a major hazard.

Surge Protection Devices (SPD or TVSS)

  1. Gas discharge tubes (GDT) should not be used as AC power line SPDs. OK to use them on signal and data lines. When the GDT “crowbars” the transient, it effectively shortcircuits the line, causing a momentary power outage for at least one-half cycle. This normally will trip the breaker.
  2. MOVs are suitable only for secondary protection in a redundant scheme. They act as high impedance open circuits until breakdown voltage is impressed. Then they begin to clamp. Specified breakdown voltage is maintained at low current, but at (lightning’s) high currents, the clamping voltage might rise higher than specified. MOVs degrade with use and their life is a function of numbers and sizes of surges.
  3. The voltage clamping of SADs is constant with use, however individual SADs are unable to absorb very much current. For this reason they are staged in a series/parallel configuration to increase total power handling capabilities. SADs provide the tightest clamping characteristics. SPDs using silicon avalanche diode (SAD) technology may develop an artificial diode bias when subjected to strong RF fields that may be present at AM, FM, or TV broadcast sites. This bias may cause data circuit errors.
  4. Common mode AC power SPDs should not be used. These devices may fail in a shortcircuit condition. Should this occur, the AC power neutral conductor becomes bonded to the ground or equipment grounding conductor, causing undesired currents in the ground or grounding conductor(s). This is a personal safety hazard and a violation of NEC. Note: Common mode circuits may be used on signal/data lines.
  5. SPDs come in packaged assemblies, and typically the above devices are staged inside. Redundant SPD philosophy is the following: Protect the Main Panel; Protect Relevant Branch Panels; Protect the Relevant Plug-ins; Protect Signal/Data.
  6. All AC power SPDs should have the International CE certification. This is a more rigorous test standard than the IEEE certification. UL certification brings even lesser testing requirements.
  7. Maintenance of SPDs enclosed within a panel requires panelboard cover removal. This work should be performed only by a licensed electrician.
  8. SPD cabinets containing MOVs should not be encapsulated. Only removable module MOVs are acceptable.
  9. Never look into a fibre optic cable. Invisible laser light is dangerous and can cause damage to the eyes.

Air Terminals

  1. A little bitty lightning rod cannot carry all the current and voltage. Where they gonna go? They will attach to all conductors, and flow according to impedances.
  2. Alternatives to rods: Overhead grounded shield wires and free-standing nearby conductive masts/poles. These indirect designs often are better than rods...so says NASA E-0013 and USAF AFI 32-1065. In some cases (for example, steel radio tower), no rods may be the answer. A rod design is very high maintenance.
  3. Air terminals are one of several lightning protection defenses or sub-systems. Others include bonding, grounding, shielding, and surge protection. Select a facility or structure of concern and rank them 1, 2, 3, etc. in order of importance.

Bonding

  1. If you don’t bond everything, your lightning protection system won’t work.

More to come, no doubt…


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