Alpha Technologies GMX-915 - Manual (Page 12)

12 017-932-B0-002, Rev. B
Grounding Connection Notes
In order to provide a ready, reliable, source of backup power, it is necessary to establish a grounding system
that provides for the safety of service personnel and for the proper operation and protection of equipment
within the network.
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 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) standards and local codes to ensure the breaker will open and prevent 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 six feet away from the driven ground rod at the power pole. The second
ground rod and enclosure are connected via #6AWG solid copper wire buried at a depth of 8 to 12 inches.
The wire is connected to 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). Connection to the ground rod is made with
a listed grounding clamp suitable for direct burial, or by exothermic weld. Normally it is specified that the
impedance of this ground can be no greater than 25 Ohms at 60Hz. However, if dual ground rods are installed
approximately eight feet apart, it is not necessary to measure the impedance of the ground rods (it is assumed
that the impedance specification is met).
Signal Ground
For proper operation, the Service Power Inserter (SPI) must be securely grounded to the enclosure chassis.
For systems utilizing ESM/DSM status monitoring, the ground connection is made through a separate chassis
ground block (Alpha P/N 162-028-10).
Strike (Lightning) Ground
Lightning strikes, grid switching, or other aberrations on the power line all have the potential to cause “fast
rise-time currents” that 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 that 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!