These wheels are designed for use in ESD (Electrostatic Discharge) environments as part of an effective ESD Control Program.
Our wheels have conductivity of <106 (exceeding the requirement of ANSI/ESD S20.20-1999 for Mobile Equipment in Protected Areas – which nominates 109 as the maximum level of resistance).
When used with plastic expanding adaptors (codes ER/ES - see Fitting Options) provisions for electrical continuity between the castor and trolley will be required.
Further technical notes follow. These notes are summaries of complex matters originally prepared as background material for the internal use of Fallshaw staff. In allowing others to access them without charge we assume no legal liability.
Nearly everyone has experienced a static shock when touching a metal object (eg: motor car, door handle) after walking for a while, particularly if dressed in synthetic fibres and wearing synthetic shoe soles.
That shock comes from a sudden flow of static electricity to earth. This is known as Electrostatic Discharge (ESD). If it is of a sufficiently high voltage, it can either ignite flammable vapours (eg. ether or chloroform) or destroy sensitive electronic equipment.
This can be prevented by ensuring there is always a pathway for the static electricity to leak slowly to earth rather than being restrained until it builds up to dangerous voltages and then surges to earth.
What causes charges to build up?
Basically when electrons are brushed off a moving surface, leaving it electrically unbalanced. Air can cause this on moving motorcars, but within buildings the normal cause is clothing fibre brushing against itself, or nearby furniture or flooring.
How high does the static voltage get?
This depends on the balance between how much is being added in, and how much can leak away. But as an example, a person clothed in a nylon uniform and wearing synthetic shoe soles, and on a hot day with low humidity, has been measured at in excess of 50,000 volts.
What can be done to reduce static being formed?
To reduce the build-up it is better if natural fibres can be used. If material used for uniforms, clothing, sheets etc, can have (at least) the majority of natural rather than synthetic fibres, this will reduce the build up, and because they are open fibres containing moisture, they allow the static charges to slowly move away rather than building up in a restricted area. The same applies to leather soles on shoes. All electrical equipment should be properly earthed.