Power Cable: To Tin or Not to Tin

09/01/2005


Throughout the engineering community there is confusion on when—and when not—to specify tinned copper conductors in power cabling applications. Why does it matter, you might ask? In an age of tight budgets and value engineering, it can mean saving your client some money or locating funding for other key systems.

In the 1950s, copper conductors in power cables were frequently tinned for three reasons: to prevent corrosion, improve stripability and improve solderability.

Today, insulation compound chemistry has come a long way, particularly regarding the latter factors. Specifically, chlorosulfonated polyethylene (CSPE) polymers, such as Hypalon, are used as an insulation or as a jacket, depending on the cable voltage. In 600-volt applications it is used as an insulation or jacket, while in medium-voltage applications it is strictly used as a jacket. When used as insulation in 600-volt cables, the CSPE is directly extruded over the copper conductor.

That being said, CSPE still contains sulfur, the element responsible for conductor corrosion, which means the conductor must still be tinned. When used as a jacket in shielded medium-voltage cables, CSPE is extruded directly over the tape shield. Again, the same argument applies here in that CSPE contains sulfur, so even the tape shield needs to be tinned.

However, there is a method to avoid tinning: Use a compound that does not contain any sulfur or other corrosive elements that can attack the conductor. Polyolefin, a compound that can be used either as an insulation or a jacket, contains no corrosive elements. In fact, polyolefin compounds often exhibit better physical properties than CSPE products. The compound's moisture absorption is lower and it has a lower coefficient of friction, better tensile strength and a lower cold-bend temperature rating. All these benefits translate into a better overall cable. Also, polyolefin compounds can be listed as limited smoke and zero halogen jackets/insulation, making them ideal for transit tunnels, power generating plants and control rooms.

More tinning alternatives

On the subject of corrosive and harsh environments, such as wastewater treatment plants and pulp and paper mills, corrosion protection is necessary where the copper conductor ends are exposed to the environment, such as at cable terminations and terminal strips.

But tinning can be avoided even in these harsh conditions by applying an anti-corrosion gel covering to the exposed copper ends. Tinning the entire conductor for the sole reason of protecting the ends is an added cost in the realm of 5% that is arguably not needed. As for the conductor length between the ends, it is protected from the environment by the cable insulation and jacket, again negating the need for the entire conductor to be tinned.

In conclusion, if you're specifying a cable insulation that has sulfur as part of its compound, such as in CSPE, then tinning the conductor is economically justified. If you're specifying tinned conductor "because the specifications always call for it," however, then you should really review its need and save some money.



How/why to avoid cable tinning

Tinning cable adds 5% to wire costs

Specify insulation coatings that do not contain sulfur

Specify that exposed connectors and cable terminations be covered with anti-corrosion gel



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