Grounding requirement

Technical Questions
#1

Dear ESD experts,
good day.
would like to seek for your advise. one of our customer is requiring us to have a 150K ohms resistor before the ground passes to the system. is it ok or safe considering that the resistance to earth going to facility would have a 150k ohms? please to seek for your thoughts here.

thank you.

#2

Rose,

I don’t see any ESD issue with this as the resistance is far below any ANSI/ESD S20.20 upper limit for a wrist strap (35 Mohms) or most other ESD control items (10^9 ohms).

#3

dear Andy,
how about grounding requirement? is tailoring required?
thank you.

#4

Hello,

My first recommendation would be to refer back to the Grounding Standard ANSI/ESD S6.1. In section 6 you will find the requirement (6.3.2 The resistance of the conductor from the common point ground to the AC equipment ground shall not be greater than 1 ohm. See Figure 8.)

Ensure your workstation grounding is in accordance with S6.1, the I would ask the customer in a respectful way what is their technical justification for not complying with the standard

#5

Hi Matt,
I am aware of 6.1 requirement however customer is insisting such. In that way can we tailor? customer cannot provide technical justification as well sad to say.
please to know your thoughts.

thank you.

#6

Rose,

I agree with Matt that you should ask the justification for this from the customer so you can better understand why they are asking for this. Still, if you need to do it a tailoring statement you could mention as a technical justification that this is a customer requirement and that 100 Kohms is significantly below the upper limit for a wrist strap (35 Mohms) and other ESD control items (10^9 ohms) and will not significantly add to the total system resistance.

#7

Dear Andy and Matt
thank you very much for the clarification.

#8

Hello Rose,

I agree with Andy. thanks

#9

For this application, I am assuming that the 150k ohm resistor is between the ground connection and the ESD control item. If this is the case, as long as the ground meets the requirements and the resistance to ground measurments meet the requirements, then there is no need for tailoring.
Just document that in your ESD control program. It most likely comes from the misunderstanding that the resistance to ground must have a lower limit to prevent CDM type discharges. That resistor does not prevent a possible CDM like discharge at a conductive worksurface it the ESDS item is charged.
The other miscoception is the resistor is there for “safety” reasons. In fact, if the resistor is there, and a metal table top is being used, this could cause a hazard.
I would like to understand why the customer requires it.

#10

Hi John,
thank you for your inputs. actually, the resistor is placed in between the ESD control item and the main earth ground. customer did not mention the requirement, it just that they want that before the earth ground pass thru the facility it will first go with the resistor.
i really don’t know the reason, but my assumption is that the safety precaution that when there are some sources of charge from the outside it will not go directly to the facility or something like that. or it could be also protection from lightning or other sources.

#11

Hello Mr. Rose,
Good evening g from India.
Already our ESDA experts have given enough clarifications. Just being a member in the Forum I also wish to pen few lines. Unlike the ESDA experts I am not an expert in the said field but, in the said field for the past two decades doing CV test audit (and in the recent past detailed PQ test too) for some customers in the Indian market.

  1. First of all, you have just stated that; one of your customers is requiring you to have a 150K ohms resistor before the ground passes to the system. You have not cleared whether you are talking with respect to Wrist strap or any other material viz; work surface or floor surface etc., However; on this context Mr Andy has given a very crystal-clear answer to your issue.
  2. As Mr. John K has mentioned, a resistor does not prevent a possible CDM like discharge at a conductive worksurface if the ESDS item is charged. And if a metal table top is being used, this could cause a hazard.
  3. However, as Mr. Matt has suggested the basic grounding guidelines per ANSI/ESD S 6.1 shall be met before connecting any ESD control materials to the Common ground point.
  4. Some users do use soft grounding soft leads (without any resistor) and some people use hard grounding leads (with up to 1 M.Ohm resistance in series) to connect the Work /floor /racks etc surfaces to ground but ultimately it is essential that the threshold resistance to ground shall not be greater than 1 x 10^9 ohms per the S.20.20 /61340-5-1 standards .
  5. Of course for wrist strap systems per ANSI-ESD S1.1 ( IEC 61340-4-6) the system resistance shall be < 3.5 x 107 ohms (as already clarified by Mr. Andy ) and only for the wrist strap assembly without the personnel per ANSI-ESD S1.1 / IEC 61340-4-6 shall be 0.8 M ohms to 1.2 M Ohms and < 5 M ohms ( per IEC ) respectively.
  6. Overall, as all the experts have suggested it would be always better asking your customers for a clarification whenever there is a deviation from the global standards.
  7. For Protection from Lightening it would be normally through the building earth which of course every builder take care.
    Thank You with Best Regards,
    Vijay
#12

thank you very much Vijay. appreciate you list all the considerations.
will definitely clarify with our customer.

with br,