Partha asks us: We have a process plant grounding system where all grade level concrete foundation of building & package skids are provided with Galvanised Steel strips, welded to the reinforcement bars. The foundation grounding bars (galvanised steel) are brought out at certain locations to connect to a copper earth bar. Electrical equipment are bonded to copper earth bars with PVC insulated copper cables. Now we are a bit skeptical about connecting Steel strip with copper earth bar because of galvanic corrosion. Can the both metals be thermowelded so that galvanic corrosion problem can be avoided..? Thanking you…
Thank you for your question regarding galvanic corrosion and copper to galvanized steel bonds. It is our pleasure to help.
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact and immersed in an electrolyte. Dissimilar metals and alloys have different electrode potentials and when two or more come into contact in an electrolyte, a galvanic coupling is set up. Scientists have indexed materials based on the nobilities of the metals. This index is called the “Anodic Index” and provides a Voltage for each material. A voltage differential greater than 0.15 Volts is considered corrosive. Copper has a Anodic Index of 0.35 and steel is 0.85. This is a 0.50 volt differential, and can certainly be a source of galvanic corrosion as the earth will surely act as an electrolyte. But there are other concerns in regards to corrosion beyond simple nobility issues, and that is induced AC currents.
Please see the following blog for more information:
Because of the good electrical conductivity and high stability in the face of short-circuit pulses, exothermic welds are one of the options specified by Article 250.8 of the 2011 National Electrical Code for grounding conductors and bonding jumpers. Also, exothermic welding is not only the preferred method of bonding, it is the only acceptable means of bonding copper to galvanized cable, according to the following:
John Crisp (2002). Introduction to copper cabling. Newnes. pp. 88. ISBN 0-7506-5555-0.
Jerry C. Whitaker (2005). The electronics handbook (2nd ed.). CRC Press. pp. 1199. ISBN 0-8493-1889-0.
We hope this useful. If you should have any further questions, please do not hesitate to contact us again in the future.
The Engineering Team at E&S Grounding Solutions
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