Lightning damage

[Eric C. Pearce]

We had similar problems (lightning zapping RS232 lines) on lines inside
our building, on both the CPU (ttya and ttyb) and the ALM.  We now have
all our lines (both ends) protected with General Semiconductor "CPP-52"
lightning protectors.  They go for about $39 each, are based on Si
avalanche diodes and have a separate ground wire.  They provide secondary
level protection with the following specs (from Gen. Semi.):

  Max. transient voltage:			2.5 KV lightning
						40 KV static discharge
  Maximum transient current (8 x 20 usec): 	190 A
  Maximum clamping voltage @ 75A (8 x 20 usec): 40 V
  Protection clamping time: 			less than 10 nsec

We have not had a failure since installing them (although we have had
other non-protected equipment get zapped and several bad storms.)

The Gen. Semi. GSI Product Data Book also had lots of other transient
voltage suppressors and a nice Application Note on protecting computer
data lines in general.

     - Eric C. Pearce
       Yerkes Observatory, University of Chicago.

       e-mail: pearce at tycho.yerkes.uchicago.edu, pearce at oddjob.uchicago.edu
       fax:    (414) 245-9125