This document is intended to clarify equipment ground and electrical grounding procedures for Tarana G1 BN and RN units. Grounding is an integral part of any installation of electronic equipment. Proper grounds are especially vital for equipment that will be exposed to possible lightning events as well as inconsistencies in available power sources. Without proper installation a site can become disabled and possibly dangerous.
This document will not attempt to summarize all of the disparate information on grounding in general nor to repeat what is available in HVAC or HAM radio specifications documents. The purpose of this document is to define and describe ground and grounding (surge protection) for Tarana equipment. Reference is also made to two industry standards, the Motorola R56 manual and the TIA standards manual, which are linked for download at the end of this document.
Ground - In electrical engineering, ground or earth is a reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.
Ground Resistance - Ground resistance is the opposition of the earth to the flow of current through it; its value depends on the nature and moisture content of the soil, on the material, composition, and nature of connections to the earth, and on the electrolytic action present.
Electrical Grounding - Electrical grounding is done with the 3rd wire on an electrical cable and connected straight to ground before entering the power distribution outlet. This protects equipment from electrical surges and a possible overload in the case of a circuit malfunction. The presence of a “ground” wire increases the degree of electrical safety for anyone using an electrical device. This is not the ground for the RN/BN units, which protects those devices from surges from the electrical circuit. Electrical grounding is usually not directly connected to ground outside of termination into the power distribution (power receptacle), however in the case of tower/outdoor installations, the power cable is subject to lightning strikes and must be connected to additional grounding at the upper and lower ends of the power cable.
General Electrical Unit
Chassis Ground - Chassis grounding is done with a grounding wire attached to the grounding lug of a G1 node that is then attached to a ground rod at the installation site for the RN or the tower grounding system for the BN. The circuit is physically connected to the ground, which has zero-volt potential to the ground (earth). This will protect the installed BN/RN from non-direct lighting strikes and provide a pathway to ground for excessive voltage. More detailed drawings for the RN are covered in the residential grounding section.
BN Tower Grounding with RN Grounding Lug
Both electrical grounding and chassis ground are always required for G1 operation.
The illustration below shows the number of lightning strikes per kilometer, per year, worldwide.
Lightning flashes per square kilometer per year
Lightning is a significant danger for any outdoor equipment such as that used for fixed-wireless access (FWA). The key to safeguarding any installation is grounding. Grounding, done properly on large tower deployments, is capable of taking indirect lightning hits many times per year and still protecting the equipment. Anyone who has done tower deployments will tell you the worst place to be during a lightning event is near the equipment deployed; it is all grounded while you are not. This is also true of any equipment that is improperly grounded.
The following sections deal with grounding systems both on towers and residential deployments. No site is exactly like any other, even for new construction sites. The use of a combination of building steel, cold water pipes, and/or new grounding systems may be needed to ensure the equipment is protected.
The illustration below shows good examples of some of the many options available.
Towers are typically engineered to have good electrical grounding and are designed to have many points at which to ground equipment. Tower owners typically have their own grounding standards, so it is always a good practice to check with the tower management company to verify their requirements before installation. The most common requirement for towers is that the connection back into the tower grounding system will usually require a robust pressure connector or cadweld connection.
Ground resistance can be verified by testing a site before and after installation and is described in detail in section D3 of the Motorola standards guide. Testing will give you an idea of how much additional, if any, grounding might be needed at a site with an existing grounding system. This will be relative to the size and type of tower and if there are collocated systems already installed.
Tower grounding systems and cadweld
Ground resistance "Meg test" kit
The G1 BN must be chassis grounded to the tower grounding system as close to the installed unit as possible. Electrical grounding must be done to the same grounding system both at the top and bottom of the tower using the DC Defender grounding system or equivalent.
Tarana’s DC electrical ground for the BN is the DC Defender 1101-1110 or DC Defender 1101-1027-2. The model used depends entirely on the gauge of the power cable.
Use the DC Defender (DC Surge Protector) w/Mounting Kit (1101-1110-KT) when the cable size used to power BN is 10AWG or smaller.
Use the DC Defender (DC Surge Protector) (1101-1027-2) and mounting kit (1000-1702) when the cable size used to power BN is larger than 10AWG.
Tarana’s Ethernet ground for electrical for the RN is the Microsemi PD-OUT/SP11. This is primarily for the RN installations at subscriber sites and is solely for Ethernet grounding and protection.
Residential deployments typically do not provide the type of grounding system a tower will, but grounding is still necessary. Most of the time a dedicated ground system will need to be installed to safeguard the equipment, the home, and everyone in it.
Some of the biggest problems that arise when grounding at non-tower locations are the size, depth, and configuration of the grounding system. Home grounds can be utilized if they exist, but depending on the date of contruction and zoning laws, the existing system may not be adequate.
RN residential grounding
The recommended grounding system for G1 mounting on a residential or non-tower deployment is an 8-foot (2.4 meters) ground rod, 2 feet (.6 meters) below the surface with a direct connection either to the equipment or distributed ground system (bus bar). At a minimum, the 8-foot / 2.4 meter ground rod should be buried with a direct connection either to the equipment or distributed ground system (bus bar).
Any data cables, with the exception of fiber, must be grounded before they enter a structure. The BN should always utilize fiber for Ethernet connectivity instead of the copper port. In addition to providing a 10 Gbps connection, using the fiber port eliminates the need for grounding the copper data port. If a copper cable is used on the BN, and for all RN deployments, the data cable grounding system must be tied into the grounding system on site as described above.
For any deployments utilizing copper, the cable used should always be a shielded cable comparable to the TRD695AHF-7 from L-Com.
Tarana’s standard Ethernet grounding is the Microsemi PD-OUT/SP11.
Correct grounding is an absolute must in any FWA equipment installation. This document discussed some of the most important aspects with respect to Tarana G1. Grounding not only safeguards deployed equipment but other collocated equipment and, in the case of residential deployments, lives and health.
For industry standard grounding specifications and guidelines see the links provided below.
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