WARNING! WARNING! WARNING! (was [Elecraft] ESD recommendation)

[Don Wilhelm]

David,

Having to study the National Electrical Code prior to building and 
wiring my house,  I can talk a bit about the safety grounding for 
residential AC power in the US -  All exposed metallic components of the 
electrical wiring system must be connected to the electrical safety 
ground.  There is an earth ground connection at the service entry point 
- which is to be the only direct ground point in the system (yes, that 
is also connected to the electrical neutral at that point - and at that 
point only). 

When an additional earth ground is used (as many hams do when driving a 
ground rod for the shack, antennas, etc), that ground rod must also be 
connected (using heavy wire) to the entrance utility ground rod - in 
fact that connection is required to comply with the National Electrical 
Code.

Under fault conditions, the use of an earth ground that is *not* 
connected back to the service entry ground can produce dangerous 
voltages between the extra ground and parts of the electrical system.

73,
Don W3FPR

David Woolley wrote:
> Modern electrical installations, at least in the UK, and I think also 
> in the US, often use a system called Protective Multiple Earthing.  
> With this all exposed metal work in a building should be connected 
> together and to the mains ground wire, but will not be connected to 
> the actual earth at the property boundary (it will be connected to 
> mains neutral).  If you have this sort of installation, you must not 
> connect anything to true earth unless you are prepared to assume that 
> you are connecting it to mains live, as, in some fault conditions, the 
> difference between the true earth and mains earth voltage can be the 
> full supply voltage.
>
> (Such installations also require special consideration with respect to 
> antennas and functional (RF) earths.)
>
>