ERICO Practical Guide to Electrical Grounding - Manual (Page 41)

33 Chapter 2: Building Lightning Protection
NFPA 780, STANDARD FOR THE
PROTECTION OF LIGHTNING
SYSTEMS - AN OVERVIEW
In addition to the general requirements covered above, the
following requirements apply to those lightning instal-
lations which must be installed in conformance with NFPA
780. Keep in mind that these requirements represent a small
portion of NFPA 780. Designers and installers who must
meet these requirements are encouraged to obtain a copy of
the standard to review all of the lightning system
provisions.
1. Section 1-3: Unless approved by the authority
having jurisdiction, all lightning system compon-
ents shall be listed or labeled. In other words, a
testing laboratory,
such as Underwriters
Laboratories (UL), must have evaluated the product
to determine that it meets appropriate designated
standards and is suitable for use in a specified
manner. Exothermic connections,
properly
installed, while not listed, are routinely approved by
UL inspectors.
2. Section 1-4: As with any electrical work performed
under the NEC, the installation of lightning
protection systems installed under NFPA 780, must
be in a neat and workmanlike fashion. While the
terms “neat and workmanlike” are undefined, this
general requirement should clearly prohibit shoddy
work on lightning protection systems.
3. Section 3-1: NFPA 780 contains two classes of
materials that must be used to install lightning
protection systems, Class I and Class II materials.
Class I materials are used on ordinary structures
which do not exceed 75 feet in height. Class II
materials must be used for ordinary structures
which exceed 75 feet in height. An ordinary
structure can be a residential,
industrial,
commercial, farm or institutional type of structure.
NFPA 780 contains charts which list the different
materials for both classes. For example, solid type
air terminals for Class I structures must be a
minimum diameter of 3/8 inch copper or 1/2 inch
aluminum. For Class II structures, solid type air
terminals must be a minimum of 1/2 inch copper or
5/8 inch aluminum.
4. Section 3-7: Any lightning system protection
components which are subject to physical damage
or displacement are required to be adequately
protected by protective molding or coverings. Metal
raceways are permitted to be used, but as with the
grounding electrode conductor, metal raceways
must be bonded at both ends to ensure electrical
continuity.
5. Section 3-9.1: In general, where air terminals are
used, they shall be mounted such that the tip of the
terminal is at least 10 inches above the object or
area it is to protect. (Fig. 2-16) However, Section 3-
11 allows air terminals to be placed at 25 foot
intervals (rather than 20 foot intervals) provided
they are at least 24 inches above the object or area
they are intended to protect. (Fig. 2-17)
6. Section 3-10.3.1: The rolling ball theory of
protection is a frequently used concept to determine
the area of protection around a building or structure
from lightning strikes. Basically, the zone of
protection is thought to include the space not
intruded by rolling a ball, which has a radius of 150
feet. In other words, if the rolling ball were to touch
two air terminals, there must be a gap between the
bottom of the rolling ball and the structure to be in
the zone of protection. (Fig. 2-18)
7. Section 3-16.1: Ground rods which are used to
terminate a down conductor must be at least 1/2
inch in diameter and a minimum of 8 ft in length.
Ground rods are permitted to be constructed of
copperbonded steel, copper, hot-dipped galvanized
steel or stainless steel. The connection of the down
conductor to the ground rod must be made by
bolting, brazing, welding or other listed high-
compression connectors. ERICO offers a full line of
high-strength, corrosion-resistant ground rods and
accessories such as CADWELD connections,
grounding clamps, couplers and driving tools to
meet the needs of contractors installing ground
rods.
8. Section 3-17: To ensure that a common grounding
potential exists for all metal objects in and around
the building, all metal objects shall be intercon-
nected, including; electrical service, telephone,
CATV, underground metallic piping systems and
gas piping systems, provided the connections are
made on the customer’s side of the meter.
9. Section 3-19.1: If the building contains a structural
steel framework, such framework may be permitted
to be used as the main conductor of the lightning
protection system provided the structural steel is
electrically continuous. (The LPI standard LPI-175
also requires the steel to be at least 3/16” (4.8mm)
thick.) Where such steel is not electrically
continuous it can be made so by the use of
appropriate bonding jumpers. (Fig. 2-19)
Grounding Book 4/14/99 10/5/99 6:01 PM Page 33 (Black plate)