Considerations for Specifying Cable Cleats
One of the most important factors when specifying cable cleats is the risk of material corrosion. This risk comes not only from the installation environment but also from other metals that the cable cleat may come into contact with.
Galvanic Corrosion
Galvanic corrosion occurs when dissimilar metals are in contact in the presence of an electrolyte. Two factors affect the rate of galvanic corrosion:
- Distance in the Galvanic Series: The further apart the two metals are, the higher the risk of galvanic corrosion. The metal higher up the list (more anodic) will corrode faster.
- Relative Surface Areas: If the more anodic metal has a smaller surface area than the cathodic metal, it will corrode faster. Conversely, if it has a larger surface area, the effects of galvanic corrosion may be negligible.
In cable cleat selection, the surface area of the cleat is typically smaller than the structure it is mounted on. If the cleat is more anodic than the support structure, it will be prone to galvanic corrosion. If the cleat is more cathodic, the risk is minimal.
For instance, with a galvanized ladder as the support structure, using stainless steel or aluminum cable cleats is generally safe. However, if the support structure is stainless steel, aluminum or galvanized cable cleats should be separated.
Galvanic corrosion is unpredictable and influenced by the type of electrolytes present, such as saltwater or fresh water with impurities. The safest course of action is to separate dissimilar metals with polymer separation washers, placed between the cable cleat and its mounting surface, as well as the cleat’s mounting fixing.
Nasco products constructed from dissimilar metals are designed to avoid bimetallic contact, ensuring a service life measured in decades.
Stainless Steel
Cable cleats are typically made from austenitic stainless steel due to its non-magnetic and corrosion-resistant properties, which prevent eddy currents and localized heating of the cable. Austenitic stainless steel can become slightly magnetic due to work hardening, but this magnetism is negligible from an eddy current perspective.
There are two principal variants of stainless steel used in cable cleats:
- 304 Austenitic Stainless Steel (A2): Commonly used for its excellent corrosion resistance, but unsuitable for coastal or marine environments due to susceptibility to chlorides.
- 316 Austenitic Stainless Steel (A4): Contains molybdenum, providing resistance to chlorides, making it suitable for coastal and offshore applications. If unsure, a simple chemical test can determine the presence of molybdenum.
304 and 316 stainless steel are available in low carbon variants (304L and 316L), which are immune to sensitization (grain boundary carbide precipitation). Any stainless steel cable cleat that includes welding should be made from these low carbon variants.
Remember: All Nasco stainless steel cable cleats are produced from 316L austenitic stainless steel.
Coatings
The corrosion resistance of stainless steel comes from chromium, which forms a self-healing layer of chromium oxide. However, in certain environments, such as railway tunnels, this layer can be penetrated by mild steel dust released from braking trains. In such cases, regular washing or the use of aluminum or coated stainless steel products is recommended.
Nasco offers special coatings for specific environments, such as electrostatic plastic coatings approved by London Underground.
Fixings
Closure fixings on cable cleats are crucial for loop strength and short-circuit withstand capability. Nasco uses 316 fixings with precise tensile strength, sourced directly from approved manufacturers, ensuring traceability and quality.
Galvanized Steel
Life expectancy guarantees for cable cleats are straightforward for stainless steel products if corrosion issues are considered. For galvanized steel, life expectancy depends on the thickness of the zinc coating. As the zinc corrodes, a tough, stable protective layer forms, but the thickness reduces over time.
For example, in a zone 3 area in the UK, the corrosion rate is 1.5 microns per year. For a 40-year lifespan, the initial galvanizing thickness must be at least 60 microns.
Remember: The corrosion rate for zinc is generally linear for a given environment.
Learn more about our cable cleats on our cable cleats page.