Don, Background: The test is intended to replicate lightning. Sending the pulse along the shield makes connections simpler, but the cable length must be sufficient to act as a transmission line; hence the 20m of screened cable.
Implementation We test CCTV equipment by coupling shorter cables together to make 20m. If the shield is grounded parasitic ground routes (e.g. multiple cameras) can divide the pulse. You may have to 'float' some equipment to force the pulse down the intended cable. Our CCTV equipment operates fine at 20m. It is better to test at 20m (even if 20m is an unusual length) than to justify an alternate test. If the maximum cable length is <2m it is exempt from the surge test, but the 2m cable limit must be specified in the instructions and/or you provide a dedicated shorter cable. David Sterner Ademco, Syosset NY -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Thursday, November 30, 2000 12:52 PM To: [email protected] Subject: Surge Testing per EN 50130-4 Hello Friends, 50130-4 Section 13 prescribes testing cables with a length of < or = 2 meters. It further states that if a screened cable is used, then a 20 meter length shall be tested. I assume the length is related to establishing sufficient coupling of the surge signal on the screen to the inner conductors. My questions are: 1) If my system contains screened cables that are less than 20 meters in length, does that mean that the screened cables are exempt from surge testing? 2) If (1) is true, then where does one draw the line -- 10 meters? 19.9 meters? What are your thoughts? Best regards, Don Umbdenstock Sensormatic ------------------------------------------- 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] ------------------------------------------- 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]
