Sender : ESD SYSTEMS, 19 Brigham Street #9, Marlboro, MA 01752-3170

Phone : 508-485-7390

This is a free monthly newsletter, which specializes on issues in static control in the workplace.

ESD Systems certifies and confirms that we have taken all necessary measures to ensure that the products and services that we supply to all of our customers are "Year 2000 compliant". Our ability to supply goods and services to all our customers will not be interrupted, delayed or otherwise adversely affected by "Year 2000 problems".

"Year 2000 problems" generally include failures, errors, delays or other events affecting equipment, production, information systems or other operations and resulting directly or indirectly from the inability of computer software, hardware or embedded chips to accurately and without interruption process or handle dates before, on and after January 1, 2000 and to process the year 2000 as a leap year.

"Year 2000 compliant" generally means that computer software, hardware, embedded chips, and products incorporating or otherwise dependent thereon, will accurately and without interruption, process data on and after January 1, 2000 and will process the year 2000 as a leap year.

NEPCON West '99 is the World's leading source for electronics manufacturing solutions.

With nearly 1,000 global companies exhibiting in over 300,000 net square feet of space, display the newest and best technological advances in electronic manufacturing. Attendees of over 31,000 industry professionals including engineers and managers involved with designing, manufacturing, testing and servicing of electronic products attend NEPCON. Attendees also include corporate managers and general managers responsible for development/management at OEMs and contract manufacturers. Industry buyers from more than 50 countries now attend NEPCON West.

As the World's leading source for electronics manufacturing solutions, NEPCON continues to meet the growing needs of the electronics manufacturing industry. From design through assembly, the solutions-oriented conference and special events provides practical information and address the questions every member of the electronics manufacturing team wants answered.

We encourage you to stop by the ESD Systems exhibit to learn more about our wide-variety of Electrostatic Discharge (ESD) Control products. This is a great opportunity to meet some of our ESD Systems’ team. We look forward to seeing you there this February 23^rd through the 25^th; our booth number is 3373.

Q1: Our ESD policy states that all equipment that is plugged into a wall outlet such as Oscopes and function generators must be insulated from the ESD mat with rubber feet of some kind.

It also states that all ESD sensitive Items must be in contact with the mat and not insulated. This is a problem when I am troubleshooting a function generator. When it is plugged into the wall, I need the rubber feet and when I unplug it, I have to remove the insulating rubber feet. Could you shine a little light on this requirement for me so I can go to the ESD police and suggest a change to our procedures. - Anonymous, Orlando, FL.

A1: Your ESD policy is designed for overall personnel safety. The reason for isolating the test equipment is to reduce the possibility of an electrical shock to a grounded (ESD Protected) operator.

The reason that ESDS devices should be able to make contact with the mat is to ensure they have a way to remove (bring into equilibrium) any charge imbalance to minimize the chance of an ESD event.

These are general policies and should have some flexibility.

There is no physical way to ground ALL conductors that make up an ESD Sensitive (ESDS) device [as all the traces on the board, pins of a chip, etc., may be guarded by discrete device packages, connectors, etc.]

All grounded operators (if they are using a quality wrist strap or foot grounder) will be grounded with a 1 Megohm resistor in series to ground. This resistor is designed in with only one purpose, the safety of the operator. UL approves quality made wrist straps and foot grounders that employ a 1 Megohm resistor in series with its ground circuit.

UL has approved our wrist straps and foot grounds up to 250 VAC because of the 1 Megohm resistor. If you are working on equipment that is under 250 VAC and grounded in series with a 1 Megohm resistor (which will limit the current to an acceptable safe value up to 250 VAC rms) then you should be able to work on this equipment and be ESD protected. THE SAFETY OF THE OPERATOR ALWAYS COMES FIRST IN ANY PROGRAM. Check with your ESD Control program administrator before changing policy.

If this is still a concern, tablemats too can be grounded with a 1 Megohm resistor to ground via its ground cable.

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Q2: What is the 1 megohm resistor placed on ESD devices for? Will it protect individuals from electrical shock and / or electrocution?

We had a DESCO coiled cord come into contact with an electrical circuit. The banana plug end came into contact with a plug that wasn't inserted completely. I am concerned that since ESD devices are meant to shunt static electricity to ground the individual wearing an ESD device might as well be standing in a bathtub with a hair dryer. - Darwin Myers, Packard-Hughes Interconnect, Foley, AL.

DETAILS:

The purpose of the 1 Megohm resistor found in series with wrist straps, foot grounders, drag chains, and ground cords is solely to provide safety to the human body by limiting the amount of current that could be conducted through your body. Underwriters Laboratory has approved selective model foot grounders and wrist straps only with a 1 or 2 Megohm resistor in series. The major dictates of the 1 Megohm resistor is that at 250 Volts rms AC, the current is limited to 250 microamps, just below the perception level (and a bit before the nervous system goes awry) of most people. Physical perception of current traveling in/on the body varies depending on size, weight, water content, skin conditions, etc.

We would not recommend grounding personnel when working with voltages over 250 VAC or 500 VDC, as described in the Cenelec Electronic Components Committee standard section 4.1.1, CECC 00015/I. Both our foot grounders and wrist straps employ a 1/4 Watt carbon composite resistor rated 250 Volts Alternating Current (VAC) and UL tested and listed for voltages under 250 VAC.

There is always a safety concern when working around high voltage. All electrical wiring and ground connections should adhere to the National Electrical Code (NEC) as governed by OSHA.

All personnel ground straps should have sufficient resistance to ground to limit current to the perception level as shown in MIL-STD-454, Requirement 1.

Section 7.3.1.3, Table VIII, (Ref.: MIL-STD-454)

Section 1.1. For areas with exposed conductors at potentials greater than 1.25 kVAC or 2.5 kVDC, additional requirements specified in CECC 00 015: Part 4 shall apply.

Section 4.1.1, The EPA shall be constructed to ensure that the equipment used to control static electricity does not create any additional risk of electric shock to personnel, should energized conductors up to the level of 250 VAC (500 VDC) be exposed.

Section 4.1.2, Additional protection against exposed high voltages: In ESD Protected Areas (EPA) where exposed energized conductors exist for each 250 VAC (500 VDC) potential the minimum resistance of any working point to ground shall be 7.5 x 10⁵ Ohms. Maximum resistance values in excess of those specified in Section 4 clauses shall not be used.

Although this standard does not include requirements for personal safety, attention is drawn to the need for all concerned to comply with relevant local statutory requirements regarding the health and safety of all persons in all places of work including those covered by this standard. (Attention is drawn to the fact that electrical potentials in excess of 50 VAC or 120 VDC may be dangerous to personnel.)

This is a free monthly newsletter, which specializes on issues in static control in the workplace.

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