Grounding and Earth Connection Notes
In order to provide a ready, reliable source of backup power it is necessary to connect the power supply to an
effective grounding and Earthing 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 provides protection with respect to operator safety, system communication and
equipment protection.
Lightning strikes, grid switching or other aberrations on the power line and/or communications cable have the potential
to cause high-energy transients that can damage the powering or communications systems. The most viable method
available to protect the system from damage is to divert these unwanted high-energy transients along a low-impedance
path to Earth. A low-impedance path to Earth prevents these currents from reaching high voltage levels and posing a
threat to equipment.
The key to the success of lightning protection is single-point grounding so the components of the grounding system
appear as a single point of uniform impedance. Two places recommended by Alpha for single-point grounding are
connections in the enclosure and connections to Earth. Single-point grounding in the enclosure is achieved by bonding
all electrical connections to the enclosure, including the connection to Earth, as close together on the enclosure as
possible. Single-point grounding for the connection to Earth is achieved, for example, by the proper bonding of the
ground rods.
Safety Ground and Earth Connection
The safety ground and Earth is a two-part system, comprised of the utility service and the Alpha system.
1. First, utility service;
As a minimum requirement for the protection of Alpha equipment, the local utility service must provide a low-
impedance path for fault current return. In addition, there must be a low impedance bonded path between the Alpha
Power Supply power plug Ground Pin and the Enclosure.
2. Second, the Alpha grounding system;
The Alpha grounding system consists of a low-impedance connection between the enclosure and an Earth Ground
(located at least 6’ away from the Utility Earth connection).
This impedance between the enclosure and Earth must be 25 Ohms or less at 60 Hertz as measured by AMPROBE
Model DGC-1000 or equivalent. The measurement should be made on the wire or ground rod after it exits the
enclosure.
Local soil conditions will determine the complexity of the grounding system required to meet the 25 Ohm (maximum)
resistance specified above. For example, a single 8’ ground rod may be sufficient to meet the requirement. In
some cases, a more elaborate system may be required such as multiple ground rods connected by a #6AWG solid
copper cable buried 8-12” below the surface. Where this is not possible, contact a local grounding system expert for
alternate methods that will meet the 25 Ohm (maximum) specification.
All ground rod connections must be made by means of a listed grounding clamp suitable for direct burial or
exothermic welding.
Power Output Return
For proper operation, the Service Power Inserter (SPI) must be securely bonded to the enclosure.
Communications Grounding
For an external status monitoring transponder, the transponder chassis is typically bonded via a separate ground wire
to the enclosure. For systems using an embedded transponder, the grounding connection is typically made either
through a separate chassis ground block bonded to the enclosure, or by means of the internal mounting hardware
which bonds the transponder through the XM2-300HP. Please refer to the appropriate Communications product
manual for installation procedures.
Alpha strongly recommends on communication cables the use of a surge arresting device electrically bonded to the
Alpha Enclosure.
Low impedance grounding is
mandatory for personnel safety
and critical for the proper
operation of the cable system
.
WARNING!
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017-877-B1-001 Rev. A
