ETL 1110-9-10(FR)

5 Jan 91

Where:

I =

8.2 amp (Current requirement from item

10 of paragraph 2-3a)

IA =

1.0 amps/anode (Current

rating

per

anode from table 3-3)

N

=

8.2

=

8.2 anodes; use nine, 2-in.

1.0

by 60-in. packaged rod

anodes

4)

Calculate the resistance of a single anode-to-earth

(RA) from equation 1-6:

RA =

L

Where:

4500 ohm-cm (Soil resistivity

from

item 1 of paragraph 2-3a)

K

=

0.0234 (Shape function from table A-4

[where: L/d = 60 in./2 in. = 30])

L

=

5

ft (60

in.)

(Effective

anode

length).

d

=

2 in. (Anode/backfill diameter)

RA =

4500 x 0.0234

5

RA

=

21.06 ohms

5)

Calculate the number of anodes required to meet

maximum anode groundbed resistance requirement.

A

distributed anode array does not lend itself to an

exact calculation of equation 1-11 because the anodes

are positioned at various locations and are not

located in a straight line. Equation 1-11 assumes a

straight line configuration. However, to approximate

the total anode-to-earth resistance, equation 1-li may

be used.

35

Integrated Publishing, Inc. |