ETL 1110-9-10(FR)

5 Jan 91

to be protected to assure uniform distribution of the

protective current to all structure components. The

higher the soil or water resistivity, the further away

the ground must be located. For this example, previous

experience has shown that the nearest anode should be

located a minimum of 100 ft from the structure to

assure good current distribution. Since there are no

other underground utilities in the area, the groundbed

may be installed either perpendicular or parallel to

the pipe (figures 2-IA and 2-lB).

8)

Determine the

total

circuit

resistance

(RT)

from

equation 1-3:

RT = RN + RW + RC

Where:

RN =

Groundbed resistance-to-earth (ohms)

RW =

Header cable and resistance (ohms)

RC =

Pipe-to-earth resistance (ohms)

a)

RN

=

1.67 ohms

Specify anodes with individual lead wires of

sufficient length so that each anode wire can be

run directly to the rectifier without splices.

(This is virtually always true for anode bed

designs where the individual lead wire lengths

required do not exceed an average of 400 ft.)

b)

Anode lead wire resistance from equation 1-15:

c

LW RMFT

RW '

1000 ft

Where:

LAVG =

Total of each actual lead wire

lengths/number of anodes

=

(140 ft + 120 ft + 100 ft + 80

ft + 60 ft + 40 ft)/6 anodes

=

90 ft per anode

LW

=

LAVG/N

=

90/6

=

15 ft

28

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