(2) For further assistance and guidance in the design of
cathodic protection systems for elevated cold water storage tanks, see Figures
102 through 104.
(3) The HSCBCI anodes were selected for this particular design
purely for illustrative purposes. It does not mean that this material is
superior to other types of anode material. Other acceptable anode materials
include aluminum and platinized titanium or niobium. With the advent of newer
tubular center connected anodes, the designer should choose these anodes over
the end connected in most cases because of their higher current capability and
(4) For this design, silicon cells should be specified for the
rectifier that protects the bowl and selenium cells should be specified for
the rectifier that protects the riser. Silicon cells operate more efficiently
at high dc output voltages than selenium cells do but require elaborate surge
and overload protection. This protection is not economical in the low power
consuming units. A guide for selection of rectifying cells is as follows:
Use silicon cells for single-phase rectifiers operated above 72 V dc or
three-phase rectifiers operated above 90 V dc. Use newer nonaging selenium
for single-phase rectifiers operated below 72 V dc or three-phase rectifiers
operated below 90 V dc.
Elevated Water Tank (Where Ice is Expected). Impressed current
cathodic protection is designed for an elevated water as shown in Figure 105.
The tank is already built, and current requirement tests have been made.
Anodes must not be suspended from the tank roof, because heavy ice (up to 2
feet thick) covers the water surface during winter. The weight of this ice
could not be tolerated on the anode cables, so another method of support is
used. Button anodes must be mounted on the floor of the tank and lightweight
platinized titanium anodes must be suspended in the riser from the tank