ESD protection electrical safety

For ESD protection reasons all the electrostacic charges on the humans and dives shoudl be avoided. Electrostatic charge buildup is generally avoided by in a way or another grounding everythign which can get a charge. In typical work environment this means that all the tables and floors mare made from a conductive material and they are grounded. The people working on this kind of inviroment them use conductive shoes and a grounded band on their wrist to keep themselves grounded.

This arrangemenet is very effective for avoiding electrostatic voltage buildup, but also makes the working enviroment potentiall very dangerous to people who are working with electricity there. If you are well grounded and touch something with some high voltage on it, you can get easily a very large and dangerous electrical shock. To avoid this danger, people in this kind of enviroment are not directly grounded, but through a resistor which limits the current flowing through the people to safe value in case they touch somethign with high voltage on this. Typically this current limiting is done using 1 megaohm resistor in the grounding wire from table tops and condictive band on the wrist. This 1 megaohm resistor limits the current to much less than 1 milliampere if you happen to accidentally touch a wire with mains potential (120V or 230V depending on country).

For safety reasons it is essential that there is is that current limiting resistor where it should be (not shorted or wrong value) and for ESD protection resons in is essential that there the ground connection is not accidentally cut for any reson. This kind of strong demands will indicate, that there is a need to tet the effectiveness and safety of the ESD protection prefererably every time before starting to work on ESD protected workplace.

For this reason there are commercially made testers sold by the same companies which sell those ESD ptotection devices. If you are a commercial user, it might be a good idea to buy a one when you buy the ESD protection stuff.

In some cases if you are a homebuilder electronics hobbyist, you might still want to have this kind of test features, but no not want to pay for the premium price of a commerial device. Basically the measurement on this kind of case is wuite easy to do, if you know what to measre. To helpp you on this, I have collected some data from one commercial measurement device to give you some idea what to do.

This in this example device used 24V DC voltage to test the resistance. This voltage is high enough for measure resistance in megaohms value and gives realistic operation enviroment results, but still low enough to be safe to use. That particular unit had the following limits for conductive bands on the wrist:

Failed to protect agains ESD:  resistance > 35 Mohm
Safe and effective:            35 Mohm > resistance > 0.75 Mohm
Dangerously low resistance:    resistance < 0.75 Mohm

For conductive shoes the values were somewhat different:

Failed to protect agains ESD:  resistance > 35 Mohm
Safe and effective:            35 Mohm > resistance > 0.1 Mohm
Dangerously low resistance:    resistance < 0.1 Mohm