[ProAudio] Proper Grounding Replies

[Corey Bailey Audio Engineering]

Hi Scott,

Well, I did it.

Based on the information that you provided below, & the replies of 
others, I took another look at the situation. It turns out that the 
cable company had run a lightning ground to the ground stake that I 
installed & didn't tell me about it. That did it! I disconnected from 
that stake & 4 days later, I have been able to connect three of the four 
AC outlets in that room to the service entrance. So, now that room is 
75% legal. ;-)

Thanks to all for your replies.

Corey

Corey Bailey Audio Engineering
www.baileyzone.net

On 11/5/2019 4:39 AM, Scott Dorsey wrote:
> Right, and this is terrifying.  Because now you have some outlets whose
> ground pin is connected to your ground rod, while the neutral pin is bonded
> to ground at the main panel and connected to the building's ground rod.
> And there's what, maybe fifty or a hundred feet between them?
>
> Let's say lightning strikes the earth a couple thousand feet from your
> house.  Current flows through the earth and for a fraction of a second
> there's a voltage gradient across the earth because the earth does not
> have zero impedance.
>
> And that means you're likely to have a few hundred volts between your two
> ground rods, meaning you have a few hundred volts between neutral and PE
> pins on the outlet, and that is not beneficial for your equipment.
>
> This is why "unbonded double grounds" are very specifically called out
> in the NEC as being forbidden.
>
> Now, the problem with the NEC is that it very explicitly tells you what
> to do, but it doesn't explain why to do it that way.  Section 250 on
> grounding lays out very good practice, but sometimes it is difficult to
> understand why these things are good practice.
>
> The unbonded double ground problem is mostly seen when cable TV companies
> hire homeless crackheads to do installations and they do not correctly
> install the cable system ground.... next thing you know there's a storm
> and people wonder why their TV set exploded.  You can run a lot of current
> from the building ground to the cable ground but only so much before something
> has to give.
> --scott
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://bach.pgm.com/pipermail/proaudio/attachments/20191109/523b7eaa/attachment.html>