RE: Static Discharge
At 01:29 PM 9/18/00 -0400, Mike_S_McCormack@ne.3com.com wrote:
>While it may not be an issue for 802.3af to directly concern itself with, I
>believe that cable charging is a real phenomena and if recollection serves me,
>Geoff was going to convene an 802.3 adhoc on the problem at the next
>plenary. I
>can't say I believe that cable charging is necessarily addressed in the power
>standard directly, but it will be a product reality we will all have to deal
>with.
I can confirm this. Contrary to what everyone believes, Ethernet with cat-5
IS used outside. Fiber is preferred, but not everyone can afford it. Cat-5
allows us to sell 10/100mbps to homes. We use an external rated cat-5 cable
and static discharge is THE problem. Lightning is NOT. (the spans are short
- like under 100m). The charge is wind induced on the P/E sheath and is
enough to nuke a switch (located up the pole).
We simply use TVS devices and correct earthing to solve the problem. The
discharge will go thru the isolation transformers and hit the switch chip.
The effect is also noticed on fiber cables and shows as corona burning on
the sheath.
rich
richard.naylor@citylink.co.nz