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Instrumentation cables commonly include drain wires, which are essentially tinned copper conductors used alongside metallic shields to guarantee effective grounding and prevent dissimilar metal reactions. Virtually every cable listed in an instrumentation cable catalogue features these drain wires, serving critical functions across diverse industrial processes. For instance, marine cables often integrate drain wires made from tinned marine wires. In this article, we further discuss drain wires in instrumentation cables and their specific purposes.

What are Drain Wires in Instrumentation Cables?

As mentioned earlier, drain wires are utilised in instrumentation cables in combination with metallic shields to ensure effective grounding. They serve to finish an electrical circuit from the shield and carry undesirable electrical noise away from the circuit. Typically grounded, these drain wires establish contact with the metallic sides of shielding tapes. Without a drain wire, connecting the tape to an earth terminal would be a formidable, if not impossible, task.

Commonly made from tinned copper, the tin coating serves a dual purpose: preventing dissimilar metal reactions between the aluminium screens and the copper conductors and enhancing the drain wire’s overall durability. Instrumentation cables designed for electromagnetic protection in inherently safe circuits often incorporate drain wires as a standard feature. 

Major Purposes of Drain Wires in Instrumentation Cables

  • To allow for effective grounding

Essentially, a drain wire authorises a low-resistance and continuous connection to the metallic shield of a cable, thereby leading to a very effective grounding. The wire stays in contact with the shielding tape’s metallic side throughout the cable’s body. This puts the drain wire in a perfect position to have a shielded cable connected to its ground terminal. For the cable, this means that it is effectively secure and protected against electrical surges that inevitably occur occasionally.

  • To prevent dissimilar metal reactions

Tinned copper conductors are typically used to create drain wires. This kind of tin coating helps prevent reactions from happening between the wire’s copper conductor and the aluminium screen next to it. The lack of such a reaction means that shielded cables can already be utilised for an extended period.

Oftentimes, when two reactive materials are positioned inside a wire next to each other, the combination of electricity and heat inside can form a chemical reaction that corrodes the insides of the wire and minimises its life cycle. Due to the composition of the drain wire, shielded cables are secure from such an event.

  • To eliminate undesirable electrical noise

The metallic shield of an instrumentation cable can only be genuinely effective if there is a way to finish its circuit within the cable. An essential part of completing such a circuit is the drain wire, which ultimately permits undesirable electrical noise to be redirected toward the ground. This kind of noise can result in significant damage to the electrical equipment if left unchecked or not removed right away. As such, it is necessary to fully eliminate electrical noise, and this can be achieved with the use of drain wires.


Drain wires play a significant role in ensuring the safe and efficient use of instrumentation cables. They essentially permit effective grounding, prevent dissimilar metal reactions, and remove undesirable electrical noise, all of which can disrupt industrial operations or damage electrical equipment. For more information about drain wires and instrumentation cables, you should not hesitate to consult an industry expert like Cable Source.

Cable Source is a reputable provider of various robust cables and wires that can be used for different applications across industries, such as instrumentation cables, marine cables, earth cables, offshore cables, and a lot more. Aside from this, we also provide high-quality cable drums in Singapore that can effectively streamline any operation requiring the use of cables. Please do not hesitate to check our website to learn more about our products.