[TenTec] ufer ground?

[Jim Brown]

On 8/12/2013 7:03 AM, GARY HUBER wrote:
> My previous work place used a Ufer ground mat (basement floor rebar of 
> all buildings of the complex) bonded to building steel (and pilings) 
> with copper grounding bars bonded to them. An external ground ring 
> with ground rods was bonded to each vertical building steel member, 
> with air terminals (on each building roof) bonded to building steel. 
> Copper grounding bars in 14th story equipment room were connected to 
> the ground mat with a 250 foot run of a pair of 400 MCM cables. The 
> electrical service neutral and mechanical ground were also referenced 
> to the ground mat. 

Everything sounds exactly right about that except the separate 250 ft 
run, which is certainly legal, but would just as well be done to 
building steel on the 14th floor. The virtue of going to building steel 
is that there are many paths in parallel, and they are all bonded 
together at multiple points, which does two very important things. The 
paths are in parallel, thus minimizing the inductance to earth (a much 
greater component of the impedance to earth than the resistance), and 
the bonds between them at adjacent points minimizes the potential 
difference between adjacent points.  Indeed, bonding all the grounds is 
REQUIRED, not optional.

73, Jim K9YC