Grounding & Earthing

Grounding Method

Grounding (also known as "earthing") is regulated by local electrical codes.  There can be health & safety risks as well as fines for code non-compliance when performed improperly or not at all. Aruba cannot accept liability for grounding decisions - these are solely customer responsibility.

 

For this reason, grounding should always be performed by a licensed electrician with detailed knowledge of local electrical codes.  Preferably a master electrician, because our experience is that most electricians don't have experience with radio systems.

Grounding procedures are covered in detail in the Installation Guide for each outdoor AP product.

In summary, each and every AP installed outside on a pole of any type, or above a rooftop must be properly grounded.  Every Aruba outdoor AP includes a ground lug to which a grounding conductor (usually copper) can be bonded. 

The recommended dimensions of a grounding conductor is a minimum cross section of 6 millimeters.  This is fairly large.  The proper way to bond the wire is actually to use a "grounding strap" to bond to the chassis, and then connect the strap to the actual ground conductor that goes to the building ground system.  Sometimes a dedicated ground must be installed if there is no nearby pre-installed grounding system.


300px-Groundstrap.jpg

A ground strap is shown in figure 1.  One end is designed to be screwed into the AP chassis with the screw provided in the box.   The other end is actually an adjustable clamp into which the copper grounding conductor is inserted.

 

Aruba does not provide the grounding straps in the box for cost reasons.  The price of copper fluctuates greatly, and the straps also add shipping weight.  They can be purchased by the local installation team prior to deployment.

 

Here are links to the correct bonding straps that should be purchased to attach an Aruba outdoor AP to a 6mm cross section grounding wire:

Do I need to ground APs below the roofline?

Ultimately this decision must be made by a licensed electrician. It is a customer responsibility to perform this in a legal and safe manner.

 

That said, there is general agreement that APs mounted to the exterior of a building well below the roofline are covered by the buildings "cone of protection" from the building earthing system. (Obviously - judgment is required here - if the structure to which you wish to mount does not have an earthing system then this guidance does not apply).

In this case, APs are treated like security cameras or other electronic equipment commonly mounted around the exterior perimeter of the building.

Again, the customer is responsible to consult with their licensed electrician to make the final determination.

 

Do I need to individually ground the LAR-1 or LAR-24?

No.  So long as the AP chassis is properly earthed.

You will find a ground ring with a crimp-type connector in the box for both the LAR-1 and LAR-24.  However, use of this is only necessary if the AP itself is not grounded (which should never ever be the case).

In the event of a discharge event, the impedence of the ground path through the chassis is lower than the impedence through copper grounding wires run directly to the LARs.  So even if you properly hook up individual copper cables with 6mm cross sections to each LAR, discharge will flow through the chassis anyways.

Given the cost of copper wire, the cost of labor to connect ground lines, and the poor appearance of having many ground wires running to individual antennas, this is an obvious benefit for all Aruba customers.

LARs should be properly torqued and weatherproofed as documented elsewhere in Arubapedia and our Installation Guides.  

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‎09-26-2014 04:44 AM
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