What is meant by “auxiliary ground” in Table 1 of the ESD S20.20 standard? Would the following situations be considered as examples of this condition?
Stainless steel plate placed on the floor of the workbench
Metal nitrogen gas pipeline
Metal workbench
Wire from a dedicated ground rod for electrostatic discharge (ESD) purposes
For situations 1, 2, and 3, would it be sufficient to connect these items to the equipment grounding conductor? And for situation 4, must it also be connected to the equipment ground?
An auxiliary ground is a grounding system used to connect parts to ground for reasons other than safety. I would consider your second and fourth items as examples of auxiliary ground as they are large enough and are connected to the equipment grounding conductor. The first and third items would more likely be an equipotential ground if isolated from ground or a common point ground if connected to the equipment grounding conductor
If the ground electrode connected to the wire is only a section of steel bar buried in the soil, and the buried depth is only 30cm, as long as the wire is connected to the equipment grounding conductor, can it be used for ESD mats and wrist strap grounding?
If you are electrically connected to the equipment grounding conductor, it should be fine to be the ground reference for any ESD control items, regardless of if it is also connected to a separate ground electrode.
Hello,
Greetings from India to all .
In my opinion, (4) Wire from a dedicated ground rod for electrostatic discharge (ESD) purposes is nothing but an auxiliary ground and, it must also be connected to the equipment ground per ansi esd s 6.1 and the bonding resistance shall be < 25 ohms
In case there is no physical grounding possible then connecting an EPE to the metal body of the work bench will be an equi potential ground which shall be <1x 10e9 ohms
When an EPE is connected to the EG through any possible AG then the bonding resistance shall be <25 ohms .
In most of the cases( at least in India I am referring to ) as a safety measure too many users prefer a separate ESD earth ie. an auxiliary earth which will be connected to the equipment earth to maintain equi potential.
While connection to direct EG is preferred earth, in that case the impedance shall be <1 ohms per ansi esd s6.1
You are right, Sir.
That it was a lot of time ago when customers come from East were absolutely surprised that we in Europe use safety ground as ESD protection. They have a lot worse experience with this, I afraid due to the troubles with EMI within power supplying wires and lightnings when they use building installation for grounding. I remember the drawing made in Malaysia or country close to Malaysia in 1990s showing separate installations, one for safety (PE), one for lightning protection and the special installation for ESD protection with the minimum distance between rods mounted into soil/earth. Neverless what somebody uses - resistance should be within limits showed by S20.20. I think.
Am I correct in understanding that if a facility already has electrical grounding (equipment grounding), it’s unnecessary to construct a separate grounding electrode outside the building specifically for ESD control?
Greetings of the day to all from India .
YES. You are correct in understanding that if a facility already has electrical grounding (equipment grounding), it’s unnecessary to construct a separate grounding electrode outside the building specifically for ESD control PROVIDED, the impedance is less than one ohm and you monitor regularly to ensure that the neutral to ground voltage shall not be greater than 2 v
Just to add on to what G S said, ANSI/ESD S20.20 does not require a separate grounding system for ESD control but some countries or companies do require it. I believe China requires a separate ESD grounding system even though many companies don’t know it.
When you mentioned that the impedance is less than 1Ω, is it means the earth impedance of the equipment grounding electrode being less than 1Ω, or the impedance between the equipment grounding wire and the neutral wire being less than 1Ω? In addition, what considerations is the requirement of the neutral wire voltage being lower than 2V based on?
It seems so, but there are many people who don’t think so. I also have a question, after the auxiliary ground for ESD control is connected to the equipment ground, may the latter affect the release of static charges?
The auxiliary ground should be able to transfer any release of static charges to the equipment grounding conductor as long as they are electrically bonded together.
I apologize for coming late to the discussion. However I would recommend getting a copy of ESD TR20.20 from the ESD Association website (if you do not already have one). It has a great section on grounding that may give you some more understanding of the types and uses of the types of grounding methods mentioned in S20.20
