ESD Clothing and Straps

The following are products a person can wear to help protect against ESD while maintaining great style.

Digi-key Static Control Clothing and Static Control Grounding Cords, Straps

Heel Straps – Also called shoe straps, are straps you wear on your shoes, with a conductive ribbon that inserts into your shoe. The straps work with the moisture between your feet/socks and shoes, this is why testing varies from person to person and dependant on the environment you are in. With wearing these heel straps, you should also have a tester to make sure the straps are working properly as they can become defective over time. These straps will ground your body so ESD will have an easier path to ground instead of the component. Heel straps are meant to be used when the person is standing and will NOT work if the person is sitting.

Heel Strap Placement: Install a heel strap on each shoe. Make sure to tuck the long ribbon strip inside the shoe or socks to make good contact with the moisture generated inside the shoe. The foot-contacting strip does not need direct contact with the skin to work correctly.

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Note: There are many different types of heel straps and for the most part work the same way, the most common is shown. Also, there are special ESD shoes that don’t require heel straps.

For heel strap testing: if you pass (green) that means the resistance of the person to the plate through the heel strap is <35 MΩ (less than 35 million Ohms). Failing high (red) means there is high resistance and If either heel strap indicates a failure, reposition the strap to make sure that contact is made to the moisture inside the shoe and retest. The goal of course is to create the path of least resistance. If a failure is still indicated you should replace the heel strap and retest.

Another indicator is if heel strap tests low (yellow), indicating a person may have a low resistance failure. This means that the resistance to ground for the person is <750 kΩ. This would not be considered an ESD issue but a safety issue and personnel should be aware of this when working with energized electrical systems. The heel straps typically have a 1 MΩ resistance in each heel strap so the combination of standing with 2 feet on the tester results in 500 kΩ resistance to ground. Most people have skin resistance above 1 MΩ so that their total resistance is above the 750 kΩ low resistance setting of the footwear test.

Wrist straps – These straps you wear around the wrist and will connect to a table monitor or wrist strap monitor. The grounding connector will be connected to the same table ground or have its own grounding sensor. These are what you would use if you are going to be seated while you are touching components.

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To test Insert the wrist strap connector into wrist strap tester. Touch the hand contact plate of the tester and observe the results. The wrist strap tester is set to show “good” via a green light if the resistance of the wrist strap assembly and person is <35 MΩ (less than 35 million Ohms). If a wrist strap fails, indicated by red light, check the ground cord for continuity by snapping the wrist strap connection end onto the tester and depress the test button. “Wiggle” the ground cord termination ends and watch for any indication of intermittent continuity. Replace the ground cord if any intermittency is observed. If the ground cord tests good, replace the band with a new one and retest the system.
Some systems combine the table with the wrist strap and monitor both simultaneously. Below you will see the wrist strap monitor on left and table monitor on the right.

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ESD jacket – ESD jackets or smocks are an ESD safe barrier between your body/cloths and the components you are working near. These smocks have conductive thread sewn into it and with heel straps, transfer ESD to ground. These wouldn’t be considered a requirement in normal settings but should be used with highly static-sensitive components that are sensitive to voltages of greater than 10 volts HBM, but less than 100 volts HBM or less than 200 volts CDM.

More info on HBM/CDM

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Some other products you can use but are not used as often:

ESD gloves- Can add ESD protection and helps keep oil from your skin off the components. Works much like the smocks with conductive threads sewn in.

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Finger cots – Made of nitrile rubber or latex this provides ESD protection on the fingers if you’re not into wearing full-sized gloves.

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Socks – Can never have too much ESD protection, works with heel straps to ensure grounding.

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For more products visit Digi-key.com

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