ERICO Practical Guide to Electrical Grounding - Manual (Page 100)

The electromotive series (Table 6-1) lists several materials
from the most anodic, or most active, at the top of the list to
the most cathodic, or least active, at the bottom of the list.
Also listed is the voltage or potential of the materials in
seawater in relation to hydrogen. Any material on the list
will protect any material listed below it.
The impressed current system uses an outside source of
electricity from a DC power supply, powered by solar, wind
or the power company. This system uses a DC current of a
magnitude greater than, and flowing in the opposite
direction to, the natural galvanic cell current. An anode is
also required with the impressed current system but it can
be of an inexpensive material such as scrap steel or graphite
(Fig. 6-5). There is practically no limit on the current output
in an impressed current system.
To conserve the current requirements for cathodic
protection on a pipeline, normal installation practice calls
for pipes to be coated to insulate the pipe from the corrosive
environment. However, these coatings are never perfect
92 Practical Guide to Electrical Grounding
Fig. 6-2
Anchor rods are also used for static grounding and
tie downs.
Fig. 6-3
A combination static grounding
receptacle/tie down.
Steel Pipe (Cathode)
Magnesuim
(Anode)
Sacrificial Anode Galvanic System
Fig. 6-4
Impressed Current Galvanic System
Fig. 6-5
Electromotive Series (In Seawater)
Table 6-1
Electomotive Series
Material Voltage
Magnesium -2.34 Most Anodic
Aluminum -1.67
Zinc -0.76
Cast Iron/Steel -0.44
Brasses -0.28
Tin -0.14
Lead -0.13
Hydrogen 0.00
Copper +0.34
Silver +0.86
Graphite (Carbon) +0.86
Platinum +0.90
Gold +1.36 Most Cathodic
DC
Anode
Steel Pipe (Cathode)
Power
Supply Impressed Current
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Grounding Book 4/14/99 10/5/99 6:02 PM Page 92 (Black plate)