Zinc Whiskers
The hidden danger in cable management systems for data centers
As many telecommunications and data centers have discovered since 1940 . Zinc whiskers are a hidden destroyer their cables and severely affected their data centers. Zinc whiskers are tiny fragments of metal whiskers that slowly grow.
A raw steel product will oxidize or rust very quickly when exposed to air. Even in a climate controlled atmosphere such as a data center, raw steel will oxidize within months. A thin coating of zinc may prevent this oxidation for years. In a typical indoor environment, zinc electroplated parts should last the service life of the building wherein they are used.
Given its anti-corrosion effectiveness and low cost prior to environmental regulation, the zinc electroplated finish has become the most common treatment for steel products in the construction industry, including communications and electrical cabling support systems such as cable tray.
One typical process for zinc whisker induced failure of electronic systems involves the (unwitting) detachment of copious numbers of whiskers by human activity.
In the case of a cable tray, the frequent movement of cables being installed or removed from the tray will easily dislodge the tiny metal filaments.
This creates an invisible fine metal dust that can become airborne in the high volume of air movement in a data center or even in a plenum ceiling space.
These whiskers are too small to be filtered by anything other than high efficiency particulate air (HEPA) filtration systems. Without such a system, the whiskers quickly find their way inside electronics enclosures. As loose conductive debris, the metal whiskers can bridge a pair of electrical conductors at differing electrical potentials and induce a variety of electrical shorting events, ranging from permanent and/or intermittent resistive shorts to extremely destructive metal vapor arcs that can cause either intermittent or complete system failure.
Finding the solution
Virtually all manufacturers of cable tray systems, whether steel wire basket, aluminum or steel ladder type, offer epoxy powder coat corrosion protection for their products. Often, however, these powder coated finishes are applied after zinc electroplating.
Some NASA research has shown that zinc whiskers can grow through a polyurethane adhesive coating if the coating is not sufficiently thick . It is unclear whether this will also happen with epoxy powder coatings.
It appears that the ideal finish would be an epoxy powder coating over bare carbon steel using stainless steel for electrical bonding. Due to EPA regulation on US domestic electroplating shops, from a manufacturing standpoint, the powder coat process is the same or lower cost as electroplating.
Epoxy powder coat finishes have been shown to be as or more durable than zinc electroplating from a corrosion standpoint while eliminating the toxic waste that is a byproduct of the electroplating process .
A powder coated tray with electroplated bonding points has a good balance of risk mitigation versus cost. The vast majority of zinc electroplated material is eliminated (or encapsulated with powder coat) with no cost penalty.
For greater assurance, a powder coated tray with stainless steel bonding points should virtually eliminate whisker related risk. However, there is some added cost estimated at 10 to 20 percent due to the small amount of more expensive stainless steel versus carbon steel.
In the most sensitive or mission critical environments, the small additional expense of stainless steel for exposed bonding points makes sense.
Considerably more expensive options like using entirely aluminum and/or stainless steel trays are also available but do not appear to provide additional benefit versus powder coating and stainless steel bonding hardware. However, given the nearly 70 years of research and data we have on the risks associated with zinc whiskers, there is very little excuse for continuing to ignore the problem.