Alpha Technologies XM3-HP Series - Technical Manual - Manual (Page 14)

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. This 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. The 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
Power Supply ground pin and the enclosure.
2. 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.
SPI
14 017-882-B0-001 Rev. C2 (10/2013)