Calculate the total circuit resistance (RT). cont'd

ETL 1110-9-10(FR)
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ETL 1110-9-10(FR)

5 Jan 91

Deep anode groundbed resistance graphs are available for

deep vertical ground beds. (See figure 2-9a through 2-9c

located in section 2-4.)

For a single horizontal anode:

4L 2 % 4L (2h)2 % L 2

(0.0052) p

RA '

(eq 1-7)

[1n

2dh

(2 h)2 % L 2

& 1]

where RA is the anode-to-electrolyte resistance in ohms, p

is the electrolyte resistivity in ohm-cm, L is the length

of the backfill cylinder in feet, d is the diameter of the

backfill cylinder in feet, and h is the depth of the

backfill cylinder in feet.

If the horizontal anode dimensions are assumed to be 6 in.

in diameter, 8 ft long, and buried 6 ft below the surface,

the following empirical expression may be used.

RA =

(eq 1-8)

441

where RA is the anode-to-electrolyte resistance in ohms and

p is the electrolyte resistivity in ohm-cm.

For multiple vertical anodes:

RN =

(0.0052) p

[(ln (8L/d) -1)

ln (.656 N))

(eq 1-9)

where RN is the anode-to-electrolyte resistance, p is the

electrolyte resistivity in ohm-cm, N is the number of

anodes, L is the length of the backfill column in feet, d

is the diameter of the backfill column in feet, and Cc is

the center-to-center spacing of the anodes in feet. This

equation assumes a linear configuration of the groundbed

anodes.

If the number of anodes used does not produce a low enough

anode-to-electrolyte resistance, the number of anodes will

have to be increased accordingly.