Alpha Technologies FlexNet ELPM 300-48D - Manual (Page 9)

9 010-322-C0-003, Rev C
Grounding Connection
In order to provide a ready, reliable source of backup power it is necessary to establish a grounding system
that not only provides for the safety of the service personnel responsible for its operation and maintenance,
but also facilitates the proper operation and protection of the equipment within the network. Such a grounding
system will provide protection with respect to operator safety, system communication, and equipment
protection.
Safety Ground
The safety ground is a two-part system. The first part is a return path for stray current back to the input
breaker, and the second is a return path from the Alpha enclosure to a second ground rod.
Typically, the safety, or utility ground, provides a return path to the input breaker or fuse panel by means of a
connection to an appropriate driven ground rod at the base of the power pole. This path must meet National
Electric Code (NEC) as well as local codes to ensure the breaker will open, preventing unwanted current flow
from posing a hazard to service personnel.
The second part of the safety ground arrangement is the ground path between the Alpha enclosure and a
second ground rod located at least 6 feet away from the driven ground rod at the power pole. The second
ground rod and enclosure are connected via an AWG #6 solid copper wire buried at a depth of 8-12 inches.
The wire is connected to the cabinet by means of a ground lug on the back of the cabinet (for pole-mounted
enclosures), or to a ground lug inside the cabinet (for ground-mounted enclosures), and connected to the
ground rod by means of a listed grounding clamp suitable for direct burial, or exothermic weld. Normally it is
specified that the impedance of this ground can be no greater than 25 ohms at 60 Hertz. If, however, dual
ground rods are installed approximately eight feet apart, it is not necessary to measure the impedance of the
ground rods to meet the maximum 25 ohms specification—it is assumed that the impedance specification is
met.
Strike (Lightning) Ground
Lightning strikes, grid switching, or other aberrations on the power line all have the potential to cause “fast
rise-time currents” which can cause damage to the powering system. Without a low-impedance path to
ground, the current, while traveling through wires of varying impedance, can produce high voltages which will
damage the powering equipment. The most viable method available to protect the system from damage is to
divert these unwanted “fast rise-time currents” along a low-impedance path to ground. A low-impedance path
to ground will prevent these currents from reaching high voltage levels and posing a threat to equipment. The
single-point grounding system provides a low-impedance path to ground, and the key to its success is the
proper bonding of the ground rods, so the components of the grounding system appear as a single point of
uniform impedance.
Low impedance grounding is mandatory for personnel safety and critical for the proper
operation of the cable system .
WARNING!