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Question With reference to article in ESD Journal "What factors affect resistance for ESD shoes when being tested while worn?" By Steve Fowler. Is this also the reason why some people have problems with foot-straps failing when tested. We have had one occasion when foot-straps were defective from the manufacturer. But it is not uncommon for people, especially in winter, to have more problems with foot-straps passing the test first time. Also the people who wear footstraps over sneakers are more likely to test first time. Would be grateful for any help with this problem, it will help us resolve something that has been bothering us for a while. - Pat Baker, Christchurch, New Zealand
Answer Exactly! Whether you are measuring the effectiveness of an ESD Shoe or a Foot Grounder, the electrical resistances from the following will directly effect the results: - the dead layer of skin at the foot before is has been moisturized- the time the foot has been in the shoe (as it starts to build up moisture)- the type of shoe (some shoes don’t breath as well and will trap more moisture in them, therefor becoming more conductive for the tab or inner sole electrical connection)- the contact resistance between foot and stocking- the material of the stocking (Gore-Tex v. cotton)- the surface area of the conductive tab or inner sole- the location of contact of tab to foot, i.e., under heel, ball of foot, arch, etc. All of these factors effect the performance of Foot Grounders as well as ESD Shoes. As always, follow the instructions from the manufacturer and allow the foot, shoe, foot grounder to come into equilibrium before testing, e.g., allow the foot to acquire the proper amount of moisture to allow the proper coupling of electrical connections (foot-sock-tab). I also agree with Steve Fowler that cotton stockings (socks) are preferable when using foot grounders or ESD shoes.
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