Wrist Strap and Footwear Testers

“My footwear tester doesn’t work, heel grounders fail high, help?”

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We occasionally hear from customers who have ESD footwear (Foot Grounders or ESD Shoes) that is failing high on their ESD footwear tester (personnel grounding tester). There is often an assumption that the issue is a faulty tester or out of spec footwear. However, most of the time the problem turns out to be as simple as a “bad match”. This is between the upper resistance setting of the footwear tester and the resistance of the ESD footwear.

The first step in identifying the cause of the problem is to identify the upper limit setting of the tester being used.

Upper Test Limits of ESD Testers

The upper limit settings on SCS footwear testers are:

ESD Footwear TesterUpper Resistance Limit
770030 Combo Tester 100 megaohm or 1 x 108 ohms (factory set)
770758 Series Dual Combination TesterThe upper limit is 1 gigaohm or 1 x 109 ohms however the factory setting 35 megaohm or 3.5 x 107 ohms
SmartLog ProThe upper limit 1 gigaohm or 1 x 109 ohms however the factory setting 35 megaohm or 3.5 x 107 ohms

Identifying the Resistance of the ESD Footwear

The next step is to identify the resistance of the ESD footwear being used, both by itself and with a person wearing the footwear.

Heel Grounders/Foot Grounders

Foot Grounder Test
Foot Grounder Test

Test Method 1 – Resistance of the Foot Grounder

  1. Using a surface resistance tester and its alligator clip, clip the lead to the foot grounder tab
  2. Clip the other lead to the cup material

This test will tell you the overall resistance of the tab, resistor (if there is one), and the cup material

If the foot grounder tab to cup resistance exceeds the upper limit of the footwear tester it’s very likely that you won’t pass on the tester.

Test Method 2 – Resistance of the Foot Grounder and Person Together

Use test method from TR53-01-15, 8.3.2 Meter, which has been summarised below:

  1. Use a surface resistance tester, a handheld electrode and a foot electrode
  2. Have the person hold the handheld electrode connect to one lead
  3. Have the other lead connected to the foot electrode
  4. Place one foot on the foot electrode making sure your other foot is not on an ESD floor or the electrode

This test will tell you the overall resistance of the whole foot grounder and person.

If the result is higher than the upper limit of your footwear tester you will not pass at the tester.

ESD Shoes

When we hear about ESD Footwear failing regularly at the personnel grounding tester, more often than not it is ESD Shoes that are failing rather than foot grounders.

Test Method 1 – Resistance of the ESD Shoes Using Foot Plate Electrode

  1. Place the shoe on a metal plate.
  2. Put the 5 lb weight from the surface resistance meter inside the shoe.
  3. Place the other weight on the metal plate next to the shoe.
  4. Lean on the weight inside the shoe and test.

This will give the resistance of the shoe itself from inside the shoe to the bottom of the shoe.

ESD Shoe test with footplate
ESD Shoe test with footplate
ESD Shoe Test with 5 lb Electrodes
ESD Shoe Test with 5 lb Electrodes

Test Method 2 – Resistance of the ESD Shoe Using Two 5 lb Electrodes

  1. Put one of the 5 lb weights from the surface resistance meter inside the shoe.
  2. Put the other weight on the sole of shoe, make like a sandwich
  3. Press the Test

See what the resistance of the shoe is using either of these methods and compare it to the testers upper limit.

Perform the TR53 test below, see what the resistance is of the person and ESD shoe while the shoe is being worn.

The same test from TR53 used for foot grounders above can also be used for ESD Shoes. This will provide you with the total resistance is of the person and ESD shoe.

Conclusion

The tests above will identify a clear discrepancy between footwear resistance and tester settings, but there can also be other factors in play. These factors should be considered when the footwear resistance and the tester settings are close to being the same.

  • Tester accuracy
  • Test voltage
  • Weight of personnel
  • Sock thickness and material
  • Humidity

Any questions regarding this post, please get in contact.

Shop the Test Equipment Used

770760

Resistance Pro Meter Kit

  • Large OLED Display
  • Internal Memory
  • Measurement Stability Modes
  • Resistance Range: 1.0 x 103 to 1.0 x 1012 Ohms
  • Under Load Test Voltages (10V or 100V ±5%)
    • Meets ANSI/ESD S20.20 resistance testing requirements for product qualification and compliance verification
  • Made in the United States of America
Learn More

770765

Handheld Electrode

  • Meets resistance measurement requirements of TR53, ANSI/ESD STM97.1 and more
  • Compatible with the Following SCS Meters:
    • 770760 Resistance Pro Meter Kit
    • 701 Analog Surface Resistance Megohmmeter Kit
    • SRMETER2 Surface Resistance Meter
  • Made in the United States of America
Learn More

A Minute with Miranda – Testing ESD Footwear

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Welcome back to “A Minute with Miranda.” This week we will be covering how to test ESD footwear entering an ESD Protected Area (EPA).

Per the ESD Handbook ESD TR20.20, A system test of the footwear in combination with the existing or proposed flooring materials in the plant should be made to ensure that the criteria for the facility are met. When using a footwear checker it is important to make sure the upper and lower resistance limits of the checker match the user’s requirements. When testing the footwear should test within the range of 1 x 106 to 1 x 108 ohms.

Heel, sole and toe grounders should be worn on both feet to ensure effective use. They should be worn by all personnel and visitors within an ESD controlled area. If worn improperly, the heel, sole and toe grounders become ineffective. ESD footwear should be tested daily before use within an ESD Protected Area (EPA).

View the full range of SCS ESD Footwear here.

The Importance of Personnel Grounding Testers

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We already know that in an ESD Protected Area (EPA) all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same potential which is achieved by using ‘groundable’ materials that are then linked to ground. We have also learnt that the most common personnel grounding device to link people to ground are wrist straps. People who are moving around should instead wear ESD footwear.

So how do you know if your wrist straps and ESD footwear are working properly? Excellent question! And one we’ll answer in today’s post so let’s jump right in!

Purpose of Personnel Grounding Testers

Wrist straps and ESD footwear should be part of your Verification Plan. Each component in an EPA plays a vital part in the fight against electrostatic discharge (ESD). If just one component is not performing correctly, ESD sensitive devices can be damaged, potentially costing your company thousands of dollars.

Wrist straps and ESD footwear can fail and damage cannot always be detected by visual inspection. Just by looking at the items you would not know if they still provide sufficient protection. Personnel grounding testers should be used to provide feedback to verify the functionality of an operator’s wrist strap and/or footwear.

Your Personnel Grounding Checklist - Wear, Verify, Log, Handle
Your Personnel Grounding Checklist

Your Personnel Grounding Checklist:

  1. Wear your personnel grounding equipment such a wrist strap and/or footwear
  2. Verify your personnel grounding system using a wrist strap and/or footwear tester. Wrist straps and footwear, need to be tested at least daily before handling ESD sensitive devices and should be worn while checking.
  3. Log a record of each test. Records should be kept for quality control purposes.
  4. Handle ESD sensitive components ONLY if your wrist strap and/or footwear pass(es) the test.

Types of Personnel Grounding Testers

Personnel grounding testers can be purchased in two configurations:

  • Wrist strap tester
  • Wrist strap and footwear tester

As wrist straps are the most commonly used personnel grounding device to ground operators, you will find a lot of testers on the market that check wrist straps only. Combined wrist strap and footwear testers will verify your wrist straps AND footwear.

In addition to WHAT the testers verify, you will also be faced with a wide range of devices differing in HOW they test. Below you will see a (by no means complete) list of options:

  • Continuous and split footplate: You will find testers with a continuous footplate which require each foot to be tested separately one after the other. Dual-footplate or independent footwear testers feature a split footplate which allows the unit to verify both feet independently at the same time. This can be an efficient time-saver if you have a number of operators in your company who are required to check their personnel grounding devices.
  • Portable, wall-mountable and fitted testers: Portable battery-powered (predominantly) wrist strap testers are suitable for small labs or for supervisors to spot-check workers and ensure compliance. Wall-mountable units are generally supplied with a wall plate which attaches to a wall; the tester is then mounted on to the wall plate. Some personal grounding devices are accompanied by a stand (and built-in footplate) which allow for a more freely positioning of the unit within a room.
  • Relay terminal: A few testers on the market are fitted with a relay terminal (electrically operated switch) that can be integrated with electronic door locks, turnstiles, lights, buzzers, etc. This can be of advantage if companies only want to allow personnel in an EPA that have passed their wrist strap and/or footwear test.
  • Data acquisition: A growing number of personnel grounding devices allow for test activity data to be logged in a database. The units link to a computer which records operator identification, test results, resistance measurements, time and more. Paperless data can enhance operator accountability, immediately identifying problems while reducing manual logging and auditing costs.

Operation of Personnel Grounding Testers

Wrist strap testing:

If you are not using a continuous or a constant monitor, a wrist strap should be tested at least daily. This quick check can determine that no break in the path-to-ground has occurred. Wrist straps should be worn while they are tested. This provides the best way to test all three components:

  • the wrist band
  • the ground cord (including the resistor)
  • the interface (contact) with the operator’s skin

The SCS Combo Wrist Strap/ Footwear Tester
The SCS Combo Tester can be used to test wrist straps – more information

“To ensure that the resistance to ground of personnel is within specification it is important to measure the entire system (i.e., wrist strap, person, and ground connection). The wrist strap system test method is described in ANIS/ESD S1.1. In general, the test method measures the resistance of the ground cord, wristband or cuff, and the interface of the band or cuff of the wearer.” [Handbook ESD TR20.20 Clause 8.2 Wrist Strap System]

“The wrist strap system should be tested daily to ensure proper electrical resistance. Nominally, the upper resistance reading should be < 35 megohms or a user-defined resistance. Daily test records can provide evidence of conformity. Daily testing may be omitted if continuous monitors are used.” [ANSI/ESD S1.1 Clause A3. Frequency of System Testing]

If the wrist strap tester outputs a FAIL test result, stop working and test the wrist band and cord individually to find out which item is damaged. Replace the bad component and repeat the test. Obtain a PASS test result before beginning work. For more information on troubleshooting failed wrist straps, check this post.

Footwear testing:

If you are using a flooring / footwear system as an alternative for standing or mobile workers, ESD footwear should be tested independently at least daily while being worn. Proper testing of foot grounders involves the verification of:

  • the individual foot grounder
  • the contact strip
  • the interface between the contact strip and the operator’s perspiration layer

“a) Place the foot grounders on the user’s shoes per the manufacturer’s instructions.
b) Place the left foot on the floor plate and touch the body contact area on the tester with one hand. Activate the tester per the manufacturer’s instructions.
c) Remove the left foot from the floor plate.
d) Repeat steps b and c with the right foot.”
[ANSI/ESD SP9.2 Clause 6.2.2 Procedure (Integrated Tester)]

The SCS Dual Combination Tester is used to test wrist straps and footwear
The SCS Dual Combination Tester is used to test wrist straps and footwear – more information

If the footwear tester outputs a FAIL test result, stop working, and test the foot grounder and contact strip individually to find out which item is damaged. Replace the foot grounder. Obtain a PASS test result before beginning work.

Conclusion

Wrist straps and footwear need to be tested at least daily before handling any ESD sensitive devices. Personnel grounding devices need to be worn for verification using a wrist strap and/or footwear tester.

A record of each test has to be kept for quality control purposes.

Only handle ESD sensitive components if your wrist strap and/or footwear pass(es) the test.