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ETL 1110-9-10(FR)
5 Jan 91
acceptable. As the required current increases, the total
resistance should be reduced. See table 3-10.
is
calculated in different ways according to the type of anode
installation. The anode-to-electrolyte resistance for a
single anode is given by RA.
For a single vertical anode:
RA =
(0.0052)
p
[ln (8L/d)-1]
(eq 1-4)
(L)
Where
RA is the anode-to-electrolyte resistance for a
single anode, p is the electrolyte resistivity in ohm-cm,
L is the length of the backfill column in feet, and d is
the diameter of the backfill column in feet.
It should be noted that the anode dimensions are the over-
all length and diameter including backfill, if the backfill
is coke breeze and is not significantly more than 2 ft
longer than the anode or not significantly more than 20 ft
longer than the anode column in a deep vertical groundbed
configuration.
For earth backfill, the backfill column
dimensions should be the dimensions of the manufacturer's
standard packaged anode can. Bare ceramic anodes shall not
be installed in ground without coke breeze backfill. Coke
breeze allows venting of gases and effectively reduces RA.
If vertical anode dimensions are assumed to be 6 in. in
diameter and 8 ft in length, the following empirical
relations may be used:
(eq 1-5)
RA =
p
398
If the anode dimensions are different, a different empiri-
cal relation may be used:
RA =
p K
(eq 1-6)
L
where RA is the anode-to-electrolyte resistance, p is the
electrolyte resistivity in ohm-cm, L is the length of the
backfill column in feet, and K is a shape function that is
selected from table 3-4.
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