Mike, I don't see the point of the short applied to the EUT side of the resistor per Fig 12.
It seems in the real world, because these are balanced lines, all lines would see the same surge. Having one signal shorted to ground generates a large current from the generator, but how does that affect the EUT? If the short were at the EUT instead of at the surge generator coupler, I could see the large amount of current setting up a field and coupling into the other conductors, albeit not much at a line length of less than 2 meters (especially when "less than" could equal "0"). It appears that we are testing the generator instead of the EUT. What real world phenomena of the EUT is being simulated by shorting the output of the coupler resistor? Best regards, Don Umbdenstock > ---------- > From: Mike Hopkins[SMTP:[email protected]] > Reply To: Mike Hopkins > Sent: Tuesday, September 05, 2000 5:28 PM > To: 'David Gelfand'; [email protected] > Subject: RE: IEC 61000-4-5 Surge Immunity Question > > Here's how it works: > > The combination of the four resistors determines the total surge current. > If the voltage is 4kV and each resistor is 160 ohms (1.2/50us generator), > the total source impedance becomes 42 ohms (2 ohms internal to the > generator in series with the 4, 160 ohm parallel resistors), and the total > current is 4kV/40 ohms, or 100A. Grounding the output side of one resistor > as shown, is the equivalent of one line being a very low impedance or > short, while the other lines are all surged. 25A is available to each line > if that line were connected to a low impedance surge arrestor or were > shorted. > > To answer your question, if one of the R's is removed, the total surge > current changes because the source impedance is now changed. Instead of > 25A in each line, there is 33A now available in each line. With the > resistor in place and grounded, that resistor takes the current that is > expected through that line, 25A, even though it is now effectively > disconnected from the unit under test. > > Mike Hopkins > KeyTek > > > > -----Original Message----- > From: David Gelfand [mailto:[email protected]] > Sent: Tuesday, September 05, 2000 4:09 PM > To: [email protected] > Subject: IEC 61000-4-5 Surge Immunity Question > > > Group, > > When earthing a line as in Figure 12, shouldn't the resistor to that > line be removed? Otherwise the surge will simply pass through that > resistor to ground. Opinions? > > Regards, > > David. > > David Gelfand > Regulatory Approvals Group Leader > Memotec Communications Inc. > Montreal Canada > > > > ------------------------------------------- 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]
