Date   : Mon, 06 Aug 2007 23:03:19 +0100
From   : pete@... (Pete Turnbull)
Subject: Suppressor (Econet)

On 06/08/2007 21:44, Johan Heuseveldt wrote:
> On Mon 06 Aug, Pete Turnbull wrote:

> The suppresors are able to protect against mains power on the network.
> That's what I've learned so far, but I could be wrong though. The diodes
> used are of the type Schottky, which are extremely fast; faster then
> anything they protects! Also, their physical size is large, as they
> need to be able to conduct 100's of amps during some time.

To stand a short to mains, they do need to be large because they have to 
withstand the mains at some amps or tens of amps for an appreciable 
time, in some cases.  That means lots of power, which means they have to 
be hardy enough not to melt before the mains fuse :-)

> Question for me is: at which are these diodes clamped to? Does that
> requires a good ground/earth connection/terminal?

Between the signal line and ground, or for differential signals, from 
each to ground and perhaps also between the signal lines.  They work a 
bit like a zener diode, and prevent the voltage across them rising above 
a certain level.

> How is the protection kept after it has kicked in? Is something
> destroyed during the process, and needs replacing afterwards?

No, the suppressor shouldn't burn out -- if it does, it will have done 
so while the fault is still present, and will therefore not have done 
it's job.  However, they're often degraded in the process, and ought to 
be replaced for continued protection.

> Indeed I think suppressors for lightning etc. are of a different type.
> So both are perhaps mutually exclusive?

They're much the same thing, actually.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York