Hello Jim, Usage of Gas Tubes is not the best choice for compliance with Overvoltage requirements. Gas tubes do not reduce the voltage to zero when they operate and they react very slowly.
Your problem can be solved in one of the following ways: 1) Replace the Gas tube with a Thyristor type of device (Such as Sidactors from Teccor). They react fast enough for ESD protection and they can handle the current of 1-2 AMPs that is required for blowing up the fuse in your card (Not the fuse in the Overvoltage simulator). I hope it is clear that the fuse you are using is rated at less than 2A on your card. 2) If you are only using a gas tube in your device without a fuse then you have very low chance of passing any of the Overvolatge tests. 3) Increase the impedance of your circuit 4) You may actually use figure 18b in clause 6.6 of UL1950 to bypass all or some the tests. Yet this is not good practice, although legally accepted. At 13:43 30/11/2000 -0500, Lyons, Jim wrote: > > >> Underwriters Laboratories is testing an ITE product for me that uses a >> three terminal 400V gas tube between tip, earth and ring of the telecom >> connection. They have failed the NAC M1 test (600V, 40A, 1.5sec) because >> the 2 amp fuse used in the wiring simulator (figure NAC.2 in UL1950 3rd >> page 239) opened during the test. >> >> The gas tube would look pretty much like a short circuit once it starts to >> conduct, and I would expect the Buss MDL2 fuse they used to blow. Their >> failure criteria would seem to exclude the use of gas tubes directly >> across the tip and ring lines. Is this a proper assumption? >> >> I would appreciate any thoughts on this situation. >> >> Jim Lyons >> >> James W. Lyons >> Manager - Product Compliance >> GTECH Corp. >> 55 Technology Way >> West Greenwich, RI 02817 >> Tel (401) 392-7723 >> Fax (401) 392-4955 >> Email [email protected] >> > >------------------------------------------- >This message is from the IEEE EMC Society Product Safety >Technical Committee emc-pstc discussion list. > >To cancel your subscription, send mail to: > [email protected] >with the single line: > unsubscribe emc-pstc > >For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > >For policy questions, send mail to: > Richard Nute: [email protected] > > Peter Merguerian Managing Director Product Testing Division I.T.L. (Product Testing) Ltd. Hacharoshet 26, POB 211 Or Yehuda 60251, Israel Tel: 972-3-5339022 Fax: 972-3-5339019 e-mail: [email protected] website: http://www.itl.co.il TO LEARN ABOUT AUSTRALIAN AND NEW ZEALAND REQUIREMENTS, CONTACT ME AT THE EARLIEST STAGES OF YOUR DESIGN; REQUIREMENTS CAN BE TRICKY! ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
