DesignSpark Electrical Logolinkedin
Menu Search
Ask a Question

26 Jan 2018, 8:54

How do Foot Grounders work?

A question we repeatedly get from customers is in regards to foot grounders. Wrist straps are generally straightforward and people understand what they do and how they work. But when it comes to foot grounders, there is still a lot of confusion out there – something we want to address in today’s post. So, let’s get started.

Purpose of Foot Grounders
A flooring/footwear system is an alternative to grounding standing or mobile workers. Where sitting personnel will be grounded via a wrist strap, this method is not feasible for operators moving around in an ESD Protected Area.

ESD foot grounders are designed to reliably contact grounded ESD flooring and provide a continuous path-to-ground by removing electrostatic charges from personnel. They are easy to install and can be used on standard shoes by placing the grounding tab in the shoe under the foot.

Structure of Foot Grounders
Foot grounders discharge static from a person to ground by connecting the person to a grounded walking surface. A conductive ribbon placed inside the wearer’s shoe or sock makes electrical contact with the skin through perspiration. The ribbon is joined to a resistor which limits current should accidental exposure to electricity occur. The other end of the resistor is joined to a conductive sole. This sole contacts a grounded ESD floor mat or ESD flooring system.

Structure of a Foot GrounderStructure of a Foot Grounder

Foot grounders must be worn on both feet to maintain the integrity of the body-to-ground connection Wearing a foot grounder on each foot ensures contact with ground via the ESD floor even when one foot is lifted off the floor. This will more reliably remove static charges generated by human movement and more reliably protect ESDS.

EN 61340-5-1 recommends a minimum of 1 Megohm resistance to ground (Rg) in order to limit inadvertent electrical current exposure to a maximum of 0.00025 amperes.

For standing operations, personnel can be grounded via a wrist strap system or by a footwear-flooring system. When a footwear-flooring system is used, personnel shall wear ESD footwear on both feet and the two following conditions shall be met:
• the total resistance of the system (from the person, through the footwear and flooring to ground)        
shall be less than 1,0 × 109 Ω;
• the maximum body voltage generation shall be less than 100 V.
[IEC 61340-5-1 Clause 5.3.3 Personnel grounding]

Installation of Foot Grounders
1. Foot Grounders with Hook-and-Loop Straps
These heel grounders are designed for use on standard shoes and can be easily adjusted to fit the individual wearer.

  • Place the foot grounder on the shoe so that the lining is making contact with the shoe.
  • Insert the contact strip inside of the shoe and under the foot. Make sure that a solid contact is made between the sock and body. Cut contact strip to the desired length.
  • Fasten hook and loop straps together, securing foot grounder firmly on the shoe.
  • Test each foot grounder to confirm proper installation.

Installation of Foot Grounders with Hook-and-Loop StrapsInstallation of Foot Grounders with Hook-and-Loop Straps – more information

2. Foot Grounders with Elastic Straps and Clip Fasteners
These heel grounders are equipped with a clip fastener, a quick release fastening system.

  • Insert the contact strip inside of the shoe and under the foot. Make sure that a solid contact is made between the sock and body. Cut contact strip to the desired length.
  • Fit the heel cup snugly to the shoe and connect the Snap-Loc fastener together. Adjust elastic strap for comfortable fit. Tuck excess elastic strap behind itself.
  • Test each heel grounder to confirm proper installation.

Installation of Foot Grounders with elastic Straps and Clip FastenersInstallation of Foot Grounders with Elastic Straps and Clip Fasteners – more information

3. D-Ring Toe Grounders
Toe grounders with the elastic D-ring fastening system are designed for use on heeled shoes.

  • Insert the grounding tab inside of the shoe and under the foot. Make sure that a solid contact is made between the sock and body. Cut grounding tab to the desired length.
  • Place rubber toe material under the area of the shoe sole. Pull hook-and-loop strap over the top of the shoe and cinch down until snug. Install so that the lined surface is making contact with the shoe.
  • Pull elastic strap around the back of the heel. Adjust D-ring plastic loop for a comfortable fit.
  • Test each toe grounder to confirm proper installation

D-RingInstallation of D-Ring Toe Grounders – more information

4. Disposable Foot Grounders
Disposable foot grounders are designed for applications where the use of permanent foot grounders is not economical or practical. They are constructed so that it may be used once and then discarded.

  • Remove shoe. Wipe any excess dirt from the underside of the heel. Remove release paper from heel grounder.
  • Apply the adhesive end to the underside of the heel of the shoe. Wrap the tape snugly around the outside of the shoe.
  • Insert the non-adhesive end of the heel grounder inside the shoe so that the black dot is well over the middle of the heel area facing upwards.
  • Put the shoe on.
  • Test each foot grounder to confirm proper installation.

NOTE: This product is not recommended for use on equipment with operating voltage

DisposableHeelGroundersInstallation of Disposable Foot Grounders – more information

Testing of Foot Grounders
Proper testing of your foot grounders involves testing the individual foot grounder, the contact strip and the interface between the contact strip and the wearer’s perspiration layer. There are a number of personnel grounding testers on the market designed to properly test foot grounders. For more detailed information on how personnel grounding testers work and how to operate them, have a look at this post. If you obtain a fail reading from the tester you should stop working and test the foot-ground and contact strip individually to find out which item has failed. Replace the foot grounder or replace the bad component if possible. Retest the system before beginning work.

Personnel Grounding ChecklistEnsure your Foot Grounders are working before handling ESDs

Cleaning of Foot Grounders
Foot grounders are to ground static charges, while dirt generally provides an insulative layer adversely affecting reliability. For proper operation, the foot grounder and its conductive strip must be kept clean. The rubber portion of the foot grounder should be cleaned using an ESD cleaner. Ensure that your ESD cleaner is silicone free. This is critical as silicone is an insulator. An alternative would be to clean using isopropyl alcohol. ESD cleaners should not be used to clean the nylon polyester grounding tab. Foot Grounders can be safely hand or machine washed on gentle cycle. Mild detergents, such as Woolite® or a liquid dishwashing product and warm water are recommended. However, care must be taken to ensure that these detergents are silicone free.

Conclusion

  • It is recommended that ESD foot grounders are worn on both feet in order to ensure that a continuous path to ground is maintained at all times (even when lifting one foot).
  • Contact strips should be tucked inside the shoe with as much contact area as possible to the bottom of the stockinged foot. ESD foot grounders rely upon the perspiration layer inside of the shoe to make contact through the stocking.
  • Foot grounders must be used with an ESD protected floor (such as correctly grounded ESD floor finish, carpet tiles or floor mats) to provide a continuous electrical path from the user directly to the ESD ground.
  • A current limiting of one or two megohm resistor in series with the contact strip is recommended but not required.
  • ESD foot grounders should be tested independently at least daily while being worn.

Desco Europe is the newest brand in the Desco Industries family, consolidating our two previous UK-based brands, Charleswater and Vermason. Desco Europe sells the full range of DII products, manufactured in our facilities in the USA and UK, servicing the European market via trained distributors who will sell the Desco Europe value package and complete ESD solution to all ESD users in their territory, leading with hi-end solutions that mark us out from the competition.

26 Jan 2018, 8:54