1

i am using a crowbar lightning protection system we built 10 years back for LAN on our own devices for the mine industry. it works very well. at that time i decided to use TVS bidirectional 18v , GDS 90v. i added 2 diodes to increase the speed of the port to 100MBPS. the capacitance of the TVS was too high. this worked for me and we did not loose any devices. but we had to replace a lot of lightning protection units, because we blow and are still blowing too many fuses. we are currently using 1/8w 3e3 resistors for fuses. i considered the TBU as from this site . but 40 volt peak seems too low for me

enter image description here

now i want to see if i can electrically isolate the input from the output by using the lan trf maybe 5000v isolation. may be still protect between the line but not to earth. will this not be a better solution

enter image description here

my current design looks like this enter image description here

what is your feel about it.

boshofff
  • 11
  • 1
  • Peripheral: You may or may not have met this 'trick'. On the cable where lightning enters make a loop in the cable of maybe 300mm diameter. Maybe two turns. Having the loop against a lightning safe (if that's a thing :-) ) grounded surface may help. Having the ground near the input point seems logical. Lightning will tend to leave the loop (the insulation obviously offering no barrier) and enter ground. This may well not limit effects beyond this point but is claimed to very greatly reduce effects. Analysis shows this "should not work" as the inductance is too low BUT it does seem to. – Russell McMahon Mar 10 '20 at 13:20
  • I got the above from an (AFAIR) Wireless World article decades ago where they went into some detail re its efficacy in a church installation with lightning tending to strike the church steeple. I've since seen it mentioned elsewhere occasionally. I've never seen it done in practice. – Russell McMahon Mar 10 '20 at 13:21
  • yes i also heard about that and i used some form of bending the wires to ensure that the lightning does enter the protector before. but that is direct hit and it was on mains cabling. i am more interested in indirect hit on signal cables. which mean the power is just elevated with a few hundred volt maybe a 1000v. – boshofff Mar 10 '20 at 13:31

0 Answers0