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 Tester||Upper Resistance Limit|
|770030 Combo Tester||100 megaohm or 1 x 108 ohms (factory set)|
|770758 Series Dual Combination Tester||The upper limit is 1 gigaohm or 1 x 109 ohms however the factory setting 35 megaohm or 3.5 x 107 ohms|
|SmartLog Pro||The 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
Test Method 1 – Resistance of the Foot Grounder
- Using a surface resistance tester and its alligator clip, clip the lead to the foot grounder tab
- 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:
- Use a surface resistance tester, a handheld electrode and a foot electrode
- Have the person hold the handheld electrode connect to one lead
- Have the other lead connected to the foot electrode
- 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.
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
- Place the shoe on a metal plate.
- Put the 5 lb weight from the surface resistance meter inside the shoe.
- Place the other weight on the metal plate next to the shoe.
- 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.
Test Method 2 – Resistance of the ESD Shoe Using Two 5 lb Electrodes
- Put one of the 5 lb weights from the surface resistance meter inside the shoe.
- Put the other weight on the sole of shoe, make like a sandwich
- 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.
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
Any questions regarding this post, please get in contact.