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ETL 1110-9-10(FR)
5 Jan 91
RC
=
0.0 ohm (Resistance of the tank-to-
water
and
negative
wire
is
negligible)
b)
Calculate the total resistance of the main anode
rods circuit (RT):
RT = 1.33 +0.13 + 0.0
RT = 1.46 ohms for main anodes.
c)
Calculate the total resistance of the stub anode
rods circuit (RT):
Where:
RN = 21.03 ohms (from step 12)
RW = 0.13 ohm (same as main anode header)
RC = 0.0 ohm (negligible)
RT = 21.03 + 0.13 + 0.0
RT = 21.16 ohms for stub anodes.
14) Design riser anode.
a)
Current requirement = 14.5 amp (from step 4)
b)
Number of anode rods required from step 6 = 15
rod segments (4-ft long each)
c)
Select riser anode system.
For proper current distribution in the riser
pipe, the anode units should not be placed too
far apart. It is generally considered that each
anode unit protects a length along the riser pipe
equal to 1 times the spacing of the anode from
the riser pipe wall plus the length of the anode.
The length of riser protected by one 4-ft long
anode located 2.5 ft from the riser wall is
therefore:
(2.5 x 1.5) + 4 = 7.75 ft
Number of anode required for a 115-ft riser:
N=
115
= 14.8 or 15 anodes
7.75
96
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