[Elecraft] K3 #1029 Build

[David Woolley (E.L)]

Dick Dievendorff wrote:
> I plug and unplug serial cables into my PC and K3 all the time without
> worrying about powering down either the PC or the K3. 

The risk with RS232C is that the grounds on the too devices may differ 
and the equalisation current might, initially flow through a signal 
connection.  RS232C is specified to tolerate all sorts of short circuits 
within its voltage range, so, if you have good ground bonding between 
the devices, you should be OK.

Note that the AUXBus, that is on the same connector on some Elecraft 
rigs is not designed to be resillient.

> 
> If equipment tended to be sensitive and were damaged by this action it would
> be common knowledge, and vendors of this sort of equipment would be have to

Nonetheless, RS232C is not designed for hot plugging.  Equipment, like 
USB, designed for hot plugging has different length pins on the 
connectors, so that ground always makes first, and any power feed second.

> deal with many customer support issues.  Successful vendors would implement
> a solution that isn't bothered by these (reasonable) customer actions.  
> 
> I've not heard that this is a problem.

Most people have good ground bonding.

I remember a case were an RS232C interface was destroyed because the 
trainee doing the cable hadn't connected the ground on the power 
distribution strip.  Current leakage from the power supplies put the 
system ground for one piece of equipment at about half mains voltage, 
albeit at a high enough impedance that it only caused a tingle.  Only 
with the serial cables engaged was it actually grounded, and inserting 
the cable risked doing the initial grounding through a signal lead.

-- 
David Woolley
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