A tale of woe, including carelessness, stupidity and laziness....

[Jay Jaeger]

On 8/26/2015 3:07 PM, Noel Chiappa wrote:
>     > From: Paul Koning
> 
>     > What happened is that the "grounds" were offset enough, and with enough
>     > of a current supply, that the ground strap that's supposed to connect
>     > the row of RP06 drives melted.
>     > This sort of thing is a major electric code violation: you can certainly have
>     > multiple services, but all the grounds are required to be connected by
>     > substantial wire; you're not allowed to stick ground rods in at
>     > multiple places and leave it at that.
> 
> I'm pretty blown away that the various grounds could be offset by that much,
> to produce that kind of current when they were tied together. Wow.
> 
> 	Noel
> 

Consider, say, 10 circuits, 20A each sharing a neutrals.  Suppose each
neutral as a total resistance of 0.1 ohm.    If the neutrals were done
properly, the voltage drop would be 20 x 0.01, or 2 V.  Share one
neutral, though, and you are up to a whopping 20V.

And if that happens, guess what:  some of the current is going to
happily use the earth ground (or an FE) as the path of least resistance.