Going Beyond the Codes: An Expanding List of On-the-Job Tips
By Richard Kithil, President & CEO, NLSI
- Don’t work on any lightning protection issues where thunderstorms
- When working around RF, wear a personal electromagnetic energy (EME)
- Always have some form of two-way communications while working alone.
Electromagnetic Energy Safety
- 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
- Aluminum ladders designed for climbing should not be used as cable
trays or runways.
- Cable separation should consider AC power, DC power, RF, ground,
and data ground cables to avoid induced interference.
- Leave all battery
issues to a battery expert.
- 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.
- 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.
- 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.
- For tower-top pre-amps that require DC voltage for operation, use
a lightning arrestor that can pass DC current.
- To pass a safety inspection, must-have items include ABC and CO2
fire extinguishers; first aid kit; interior and exterior lighting.
- Incoming coaxials must be run through weather ports (boots) that
also are rodent- and insect-proof.
- 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.
- Before excavating or digging, do the “locates.” Call
before you dig!
- 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.
- Wear safety glasses, hard hat, and steel-toed boots when working
with high-compression fittings.
- Braided bonding straps should not be used because they corrode too
quickly and can be a point for RF interference.
- Avoid differences
in potential. Do not install separate grounding electrode systems.
Follow NEC 250/IEEE 142/FAA 019d requirements here.
- Before disconnecting a grounding electrode conductor, check for
current. Never disconnect the ground of a live circuit — death
or severe injury could result.
- 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
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
- 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.
- Optimum spacing apart for ground rods is 2 X length.
- A bare copper buried ring electrode provides more conductor surface
area than many rods. Consider a ring electrode where practical.
- 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.
- 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)
- 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
- 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
- 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.
- 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.
- 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.
- 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.
- Maintenance of SPDs enclosed within a panel requires panelboard
cover removal. This work should be performed only by a licensed
- SPD cabinets containing MOVs should not be encapsulated. Only removable
module MOVs are acceptable.
- Never look into a fibre optic cable. Invisible laser light is dangerous
and can cause damage to the eyes.
- 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.
- 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.
- 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.
- If you don’t bond everything, your lightning protection
system won’t work.
More to come, no doubt…