Glossary

Equipotential bonding

Also Bonding

What is Equipotential bonding?

The conductive connection of metallic components to one another so that no dangerous voltage difference can arise between them. It is not a substitute for the return cable of a circuit.

What matters about Equipotential bonding in practice?

Confusing it with ground is the most common mistake: equipotential bonding connects components for safety reasons, the negative cable carries operating current back. Using the structure as a return turns the bonding into a conductor with undefined resistance.

On board, equipotential bonding also touches on corrosion: connected metals in water form a galvanic cell. Planning both together is a task for the system design, not for improvisation.

How does bonding differ from the negative conductor?

The negative conductor carries a load's operating current back to the battery. The bonding system carries no current in normal operation. It connects metal parts such as engine, tanks, seacocks and housings so that they sit at the same potential. Only in a fault, for example an insulation fault, does it carry the fault current so that a fuse or a residual current device can trip.

What does bonding have to do with corrosion?

Connected metals in seawater form a galvanic cell, and the less noble metal gives up material. That is why the sacrificial anode belongs in the bonding system: it is deliberately the least noble part and so protects propeller and shaft. With shore power, the protective earth connects the boat to other boats via the pontoon. A galvanic isolator or an isolation transformer breaks this path.

What to watch when installing

  • Mark bonding conductors green-yellow and route them separately from the negative conductors.
  • Keep connection points accessible and protected against corrosion.
  • Connect the bonding system to the DC negative at exactly one point, not several.

Related terms

All terms from A to Z

Still unclear?

We are happy to explain it for your specific case.

ContactTo the Academy