ESD Library

Curing Static Electricity Damage In a Communications Center

Roller Caster Electrical Test Assesses Long-Term Electrical Performance

When evaluating a static control carpet, always ask for test data. The Roller Caster Electrical Test (CET), an essential test for conductive carpet, will tell you whether or not the carpet will retain its electrical properties after it has been exposed to a year or two of chairs rolling over the floor.

Rolling casters destroy or "mash" the carbon fibers in conductive carpeting and can turn a once conductive product into an insulator. In the LaVergne County Police Department, the pre-renovation antistatic carpeting failed because the antistatic fibers, crushed by the chair casters, were no longer in contact with the dispatchers' shoe soles; as a result, the dispatchers were walking across a floor with less static protection than the living room carpet found in most people's homes.

The static control properties of a conductive carpet (see below) should always be tested before and after the CET. The CET simulates the action of a person seated in a caster chair, rolling back and forth and moving around, and assesses delamination and edge-ravel performance. Areas where roller caster chairs are in use are the most demanding of any carpet. Again, because crushed fibers can render the static control properties useless, the CET is absolutely essential for evaluating the long-term performance of a conductive carpet.
 

To make the test as rigorous as possible, an unsealed seam should be cut in each sample prior to testing. In addition, each sample must be installed over a defined cushion, which dramatically increases flexing at the seams, the most vulnerable point in any carpet. The flexing action, coupled with 198 pounds (90 kilograms) weighting and 25,000 cycles of the caster chair, imparts highly accelerated fatiguing of the carpet, seams and backing. With a regular carpet, no edge ravel or delamination should be evident after 100,000 cycles. Products that can successfully withstand this grueling test usually demonstrate outstanding field performance. Poor results help identify potential problems before the carpet is installed. Because the static control properties of a conductive carpet can be destroyed by repeated wear from rolling casters, floors with conductive yarn systems should be exposed to at least 100,000 cycles (less than two years of installed use in a 24/7 mission-critical space).

The recommended requirements of ANSI/ESD S20.20. (ANSI/ESD S.20.20 is the electrical standard endorsed by the Electrostatic Discharge Association, the international organization that sets the standards for the proper control of static electricity. With this in mind, anyone in charge of selecting a static control floor should be aware that a lifetime-time electrical warranty cannot be interpreted as immunity to caster rolling damage; most suppliers of computer-grade or ESD carpet do not even test for caster damage because it is specifically excluded from any warranties they provide.

The chair caster rolling test also revealed significant electrical performance weaknesses in certain types of static control carpet tiles. For example, tiles made with PVC backing fared very poorly in the test. There are several possible explanations for the inferior performance of tiles backed with PVC. First, PVC is a poor conductor. It is also possible that the tiles backed with PVC lacked other critical design features like insertion of conductive fiber in all the yarn ends of the carpet or that these PVC products were built with small denier (textile term for size) fragile conductive fibers. Whatever the explanation, 9-1-1 communications centers require extreme longevity from their static control floor—newer, faster, and more vulnerable electronics are constantly finding their way into the work place.

*This article appears in the August/September '05 issue of Emergency Number Professional Magazine.