[c-nsp] Grounding issues between devices

[Jordan Hazen]

On Fri, Dec 09, 2005 at 01:55:21PM -0700, John Neiberger wrote:
> Here's an interesting problem. At one of our sites we have a 2950 switch
> sitting directly on a 2620 router. These devices have rack ears attached
> but they are not rack mounted. A tech from a different group just
> informed me that he was at that site earlier and needed to move the
> network equipment, and he got quite a shock when he grabbed the rack
> ears of the switch in one hand and the rack ears of the router in the
> other. He described it as being significantly more uncomfortable than a
> shock from a 9v battery.

Check that your power outlets there are wired correctly, with a good
low-resistance ground and no swapped conductors...

EMI filters near a device's power connector often have capacitors from hot &
neutral to ground, to reduce noise escaping through the cable.  These can
let through a small current also, but that normaly bleeds off harmlessly to
ground.

Could be a defective power supply in one of the units, also.  I was shocked
once by a PC ATX supply, after its ground wire inside had come loose.

 
> The weird thing is that the chassis are touching, so I wouldn't think
> he would have been shocked even if there was some sort of grounding
> problem or some other electrical issue. Since the devices are touching,
> he wouldn't have been the preferred path. I'm not quite sure he got
> shocked, but he said it is repeatable.

Painted metal isn't a very good conductor...

 
> I suppose I'd better go check it out before someone gets electrocuted.
> :)
> 
> John
> --
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-- 
Jordan.