Earthing Site

8/13/2019 Earthing Site

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Earthing the site

Overview

The following provides information on suggested earthing procedures for outdoor anM-Cell6site. It is assumed that for indoor installations, adequate building earths will

already be in place.

The separate earth systems must be isolated from each other to facilitate periodic

testing of the earth systems. Earth inspection pits are provided for this purpose.

Earthing requirements

Each M-Cell6site eternal earth must be assessed on an individual site basis as

conditions will vary considerably depending on local soil conditions and site

topography. It is essential that a site survey and soil resistance test be performed

before installation. The site architect defines the site and foundation earthing

requirements to ensure a resistance of less than 10 ohms. ! typical site earthing

plan is shown in Figure 1-1.

Figure 1-1 Typical site earthing plan for open field site

Earth electrode system

The earth electrode system consists of a series of interconnected earth electrodes"minimum of four# that are located outside the foundation reinforcing metalwor$.

%efer to Figure 1-1for details. The earth rods should be connected together using

TCO30 solidtape conductors, avoiding any sharp bends& a minimum bend radius of

!0 mm is recommended"

Cross bonding'oundation metalwor$ must be connected to the earth electrode networ$. The earth

system must also be cross-bonded to an ad(acent antenna mast, with two connections

made between the two systems. !ll earth cable terminations must be crimped,

clamped or welded& soldered (oints are notpermitted.

Earthing #rocedure
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The M-Cell6equipment must be earthed as detailed in this procedure. Ma$e provision

for routeing the earth cables into the site and to the cabinet before beginning

installation of the system rac$s.

Ecavate the site to accommodate the foundation to a depth determined by the site

architect for M-Cell). 'or the earth components to be used, refer to Figure 1-1and

proceed as follows*

+. rive a minimum of four co##erearth rods "$ m long"./ inches# below

the surface, and connect these rods together with %0 mm"0.++1inches# Cross

2ectional !rea "C2!# solid conductor.

1. Connect the earth rods to the cabinet earth busbar via a 30 mm "0.++1inches#

C2! solid conductor.

4. Chec$ that the earth electrode installation resistance is less than 10 ohms. If

the resistance is greater than 10 ohms, install more earth rods to bring the

resistance within s#ecification"

. Cross-bond the earth system to the ad(acent antenna mast earth with

conductors of 30 mm "0.++1inches# C2!, buried at a depth of not less than

!00 mm"+.)5 inches#.

/. 6ond equipment such as fences, fuel tan$s, metal buildings, or steel building

s$ids associated with the site to the closest earthing rod or bonding wire.

Earth electrode testing

Three methods of earth electrode test "earth mat# are used and should be tested as

detailed in 623)3+ +)th Edition "or equivalent country regulations#*

'all of potential.

)+.57 rule.

2lope method.

The method of test to be used at a specific site is determined by the site conditions,

the etent of the earth system and the limitations of the site boundaries. The method

used at the site is to be determined from the earth electrode compliancy certificate and

repeated annually. 6efore proceeding with the test, ensure that the resistance of the

test leads is less than 0.0/ ohms.Fall of #otential

This method of testing is used for measuring resistance of earth electrodes but is only

practical on single earth electrode systems.

rive the current test spi$e and potential spi$e into the ground as shown in'igure +-

1. 8erform the three resistance tests and chec$ that the average of the three tests is less

than +0.0 ohms.

&1"'( )ule

This method applies when the three electrodes "earth, potential and current# can be

positioned in a straight line, the soil is homogenous and also when single electrodesystems are being used.
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2et up the test equipment as shown in Figure 1-with the potential spi$e placed at a

distance of )+.57 of the distance from the earth electrode to the current test spi$e. !

greater accuracy can be achieved by increasing the number of readings.

*lo#e method

This method applies to large earth systems. %efer toFigure 1-but insert thepotential spi$e at a number of points between the earth system and the current spi$e.

! minimum of si readings must be ta$en to plot a graph and this graph compared to

published tables to calculate the resistance.

9n completion of testing, complete and sign the earth electrode test documentation

"'orms of Completion and Inspection Certificate#.

Figure 1- Earth electrode test setup

The cell site equipment must be earthed "in the same common earth point as its power source#.

8rovision should be made for routeing earthing lines into the site and to the cabinet before

beginning the installation of the system cabinets.

There is an earthing terminal "stud# located on the interconnect panel on top of each cabinet.

%efer to the site-specific documentation for detailed site earthing information.

Transient and lightning #rotection1.05 Mbit:s lines connected to Motorola equipment have secondary transient

protection as part of the balanced-line interconnect board "6I6# or T4 board. Ensure

the receive and transmit antenna connections to the building are fed through coaial

electromagnetic protection "EM8# devices.

Cabinet earthing #oints
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Overview

+-Cell& ,T* cabinets .ndoor/

The main earth connection point on the M-Cell6indoor cabinet is a 1/ mm M+0 threaded stud on the

top panel, to the rear of the power input plastic housing. This connection is for protective earthing andfunctional earthing of the cabinet.

+-Cell& side cabinets Outdoor/

The outdoor M-Cell6has a main earth busbar plate in the side cabinet.

The main earth busbar plate is of 50 ) mm cross section, with two rows of eight

M+0 1/mm studs for ma$ing eternal earth connections on the bottom side of the

plate and a single row of eight M+0 1/ mm studs for ma$ing antenna feeder earth

connections on the top side of the plate.

+ain earth busbar

The main earth busbar must be connected to the main cabinet earth connection point via 4/ mm

1

C2!green and yellow sheathed stranded conductor. The antenna input line earths, ac input earth, and rac$frame earths must all be connected to designated earth studs on this earth plate. %efer to Figure 1-1for

the M-Cell6main earth busbar connection diagram.

+-Cell& earth #late Outdoor/The following diagram shows the M-Cell6earthing plate*

Figure 1-1 M-Cell6earthing plate

ositive earth cabinets
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To connect a positive earth cabinet to the main dc power source, Motorola recommends using a 4/ sq.mm dc input power cable with a maimum length of 1 m "50 ft.#.

'or positive earth applications "-5; dc#*

The negativepower cable is blue.

The #ositive"earth# cable is blac.

ositive earth cabinetTo connect dc power cables to a positive earth cabinet*

+. Connect the earth wire from the master earth bar to the earth stud on top of the cabinet.

1. Connect the blac$ positive "

Earthing Site

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