Wrist straps are generally straight forward with 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.
An Electrostatic Discharge (ESD) flooring / footwear system is an alternative for grounding standing or mobile workers. Sitting personnel are usually grounded via a wrist strap, but this method is not feasible for operators moving around in an ESD Protected Area (EPA).
ESD foot grounders are designed to reliably contact grounded ESD flooring and provide a continuous path-to-ground by removing electrostatic charges from personnel. ESD foot grounders are easy to install and can be used on standard shoes by placing the grounding tab in the shoe under the foot.
Per ANSI/ESD S20.20 Clause 8.2 Personnel Grounding: “For standing operations, personnel shall be grounded via a wrist strap or by a footwear/flooring system meeting the requirements of”:
- the total resistance of the Footwear / Flooring system shall be less than 1.0 × 109 ohms
- the maximum body voltage generation shall be less than 100 V.
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 electrical current should accidental exposure to electricity occur. The other end of the resistor is joined to a conductive sole. The sole contacts a grounded ESD floor mat or ESD flooring system.
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 ESD sensitive devices (ESDS).
Installation of Foot Grounders
1. Standard Style Foot Grounders
Standard D-ring heel grounders are equipped with an elastic D-ring fastening system which provides adjustable cinching of an ankle strap and allows “flex” during walking. They are designed for use on most types of shoes and boots.
- Place the grounding tab in the shoe so that it will lay under the heel. Once heel is repositioned inside tied shoe, tuck excess ribbon material into side of shoe.
- Place heel cup onto the shoe. For models with a non-marking interior, install so that the lined cup surface is making contact with the shoe.
- Pull the strap through the D-ring and cinch down for snug, comfortable fit.
- Test each heel grounder to confirm proper installation.
2. Cup Style Foot Grounders
Cup Style Foot Grounders are heel grounders 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 contacting the shoe.
- Insert the grounding tab inside of the shoe and under the foot. Make sure that solid contact is made between the sock and body. Cut contact strip to desired length.
- Fasten hook and loop straps together, securing the foot grounder firmly on shoe.
- Test each foot grounder to confirm proper installation.
3. D-Ring Toe Grounders
Toe Grounders with the elastic D-ring fastening system are designed for use with a variety of men’s and women’s shoes including high heels, cowboy boots, flat shoes, loafers and safety shoes.
- Insert the grounding tab inside of the shoe and under the foot. Make sure that solid contact is made between the sock and body. Cut grounding tab to desired length.
- Place rubber toe material under toe area of shoe sole. Pull hook-and-loop strap over top of shoe and cinch down until snug. Install so that the lined surface is contacting 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
4. Disposable Foot Grounders
Disposable Foot Grounders are designed for applications where the use of permanent foot grounders are not economical or practical. They are constructed so that it may be used once and then discarded.
- Remove shoe. Wipe any excess dirt from underside of heel. Remove release paper from heel grounder.
- Apply the adhesive end of the heel grounder to the underside of 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 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.
Advantages of ESD Foot Grounders
ESD foot grounders are often preferred over ESD shoes for several reasons:
- One size fits many foot sizes, reducing stock holdings and simplifying operations.
- ESD foot grounders usually pass the mandatory resistance test as soon as worn, whereas some ESD shoes require a ‘warm-up period’ in order for the operator’s Resistance to Ground (RG) to drop below 35 megohms.
- The operator is allowed to wear their own footwear, increasing their comfort in the workplace and not limiting footwear selection to available ESD shoe styles.
- Less initial investment cost in comparison to ESD shoes if outfitting all operators in an EPA.
Disadvantages of ESD Foot Grounders
ESD foot grounders have a useful life that is dependent on the floor and it’s surface roughness, which can make them seem like they have shorter useful life in comparison to ESD shoes. However, there are a few simple tricks to avoid a quick ‘burn-out’:
- We recommend ESD foot grounders only to be used indoors where floors are usually smoother (and where the ESD foot grounder is less likely to become wet, thereby short circuiting the resistor). The rougher the floor the greater the wear.
- The manner in which the wearer walks can also affect the life span of the grounder.
In summary, with reasonable care and if used only indoors, ESD heel and toe grounders can last several weeks.
Testing of Foot Grounders
Proper testing of your foot grounders involve testing:
- the individual foot grounder
- the contact strip
- the interface between the contact strip
- the wearer’s perspiration layer
There are personnel grounding testers on the market designed to properly test foot grounders. For more information, check out our selection chart.
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.
Cleaning of Foot Grounders
Foot grounders are used to ground static charges, however dirt provides an insulative layer adversely effecting 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 dish washing product used with warm water are recommended for cleaning, however care must be taken to ensure that these detergents are silicone free.
- It is recommended that ESD foot grounders are worn on both feet 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 system (such as properly 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 to periodically test for proper grounding.