Jim: DOD-HDBK-263 Appendix E para. 50.2 says in part "Tools and test equipment on grounded work work benches with metal or other conductive coverings can shunt the protective resistance in the work bench ground cable if allowed to contact the work surface." It's not likely that equipment will inject electrical energy into the work through the mat. One-megohm resistance from mat to ground protects the operator so that if they touch something live, the current doesn't run through them directly to ground (like standing in a puddle). That's why wrist straps and static mats have resistors in the snaps. Some mats might be resistive enough that a resistor is not needed in the ground connection, but I know that the 3M mats that we use are quite conductive, and the resistor is absolutely needed. The handbook suggests the possibility of using ground fault circuit interrupters, but Appendix G para. 30.1.f also says "Electrically powered tools, test equipment, and fixtures used in ESD protected areas should be properly grounded. Grounding of electrical test equipment should be via a grounded plug, not through the surface of the ESD protective work station." We require 3-pronged plugs or UL listing on anything electrical at an ESD protective work station. Joe Kane BAE SYSTEMS Controls -----Original Message----- From: Jim Jenkins [mailto:[log in to unmask]] Sent: Thursday, May 30, 2002 2:26 PM To: [log in to unmask] Subject: [TN] ESD and equipment isolation Hi everybody, One of our internal specifications states that processing equipment needs to be "electrically isolated" from the static dissipative mat. We are interpreting this to mean that if the equipment has a metal case it is not allowed to be in contact with the mat. There has been some controversy over this, because we have whole areas and labs that have test equipment and other items that do not have the little feet on the bottom and make contact with the mat. We have people arguing on both sides here. Some say that the contact provides a direct path to ground taking out the resistance needed to slow down the discharge. I say that the dissipative (rather than conductive) nature of the mat provides the necessary resistance. That is why resistors are no longer required in ESD specifications. Others say that the equipment can inject electrical energy through the mat into the ESDS devices. What do you all think? Thanks, Jim Jenkins [log in to unmask] ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------