# grounding and sugar sand



## oop (Sep 26, 2014)

I'm doing a job for a relative that doesn't have much money. The main panel is a 200 amp outdoor. There were no ground rods, water ground, or ground wire running to the house, but the feeders to the sub (where most of the branch circuits are) in the house were sufficient. I go to pull a new ground wire in the 1 1/2 pipe and realize that it changes over to 3/4. Can't believe someone was able to even get the wires that were in there.

The property is all sugar sand so I dig a trench to the house and run app 100 ft of bare #6 18 inches deep. Drove three ground rods and tied everything together (including water ground). I'm not tying in the house panel until I get the grounds separated in the sub.

Looking for opinions on this. On one hand it is probably going to be an excellent ground system. On the other hand, if something were to happen to interrupt the ground system, any possible fault current would be running through earth and create a pretty hazardous situation. I know it's not likely, but it is possible.

Any thoughts?


----------



## backstay (Feb 3, 2011)

Fault paths are never back through the earth, resistance is too high.


----------



## Mshea (Jan 17, 2011)

backstay said:


> Fault paths are never back through the earth, resistance is too high.


Not true, High voltage faults do go through the ground and DC faults do as well. AC faults would go through the ground if resistance was the only opposition to current flow but in an AC system the ground is too high an impedance to transmit much fault current. That said as much as 10% of the fault may travel in the ground from several experiments in the 1950s.

In AC systems almost all the fault current travels over the grounded wire (white wire) when the system is grounded but not on the ground wire (Bare wire to the electrodes)


----------



## Big John (May 23, 2010)

Theory aside, it sounds like OPs system is messed up.

You've got a remote main panel, and you've got a sub 200 feet away, that had no equipment ground and no electrode system? 

The lack of equipment grounds is a separate problem from the lack of electrodes, and addressing one does not address the other.

At both locations do you now have electrodes with a neutral conductor and a EGC run between them?


----------



## MXer774 (Sep 1, 2014)

Big John said:


> Theory aside, it sounds like OPs system is messed up.
> 
> You've got a remote main panel, and you've got a sub 200 feet away, that had no equipment ground and no electrode system?
> 
> ...


Nice question John, may I add another? How did the OP go from setting up to pull a new EGC in the 1 1/2" conduit then realize that at the end of the raceway, somehow transitions to 3/4"?
Shouldn't one see what they will be up against at both termination points.


----------



## backstay (Feb 3, 2011)

Mshea said:


> Not true, High voltage faults do go through the ground and DC faults do as well. AC faults would go through the ground if resistance was the only opposition to current flow but in an AC system the ground is too high an impedance to transmit much fault current. That said as much as 10% of the fault may travel in the ground from several experiments in the 1950s. In AC systems almost all the fault current travels over the grounded wire (white wire) when the system is grounded but not on the ground wire (Bare wire to the electrodes)


As best as I can tell, it's a residential 200 amp service. Neither high voltage or DC. And the ground rod is still a piss poor fault current path.


----------



## macmikeman (Jan 23, 2007)

Big John said:


> Theory aside, it sounds like OPs system is messed up.
> 
> You've got a remote main panel, and you've got a sub 200 feet away, that had no equipment ground and no electrode system?
> 
> ...


Maui County- legal except for the no electrodes part- still on 05 latest I heard.


Like Pipenick says- Florida is three feet over the water table most places, especially where there is sugar sand. Drive a ten foot long rod and you got 4 or 5 foot of electrode in quazi electricians soup down there. Many digs I made in either my back yard or on jobsites as a young man we hit the water at waist deep. Current will flow back to the poco's rod and up their gec well enough to trip a 15 under those conditions.


----------



## Meadow (Jan 14, 2011)

Mshea said:


> Not true, High voltage faults do go through the ground and DC faults do as well. AC faults would go through the ground if resistance was the only opposition to current flow but in an AC system the ground is too high an impedance to transmit much fault current. That said as much as 10% of the fault may travel in the ground from several experiments in the 1950s.
> 
> In AC systems almost all the fault current travels over the grounded wire (white wire) when the system is grounded but not on the ground wire (Bare wire to the electrodes)


Incorrect, DC and AC go through the earth the same way: based on the actual resistance which is often high. Ohms law applies to both DC and resistive AC. Soil is resistive, not inductive or capacitive. 


Yes AC will always have a reactive component, however that's *not* what limits 99.99% of the current on a ground rod. Its the high resistance of soil which varies on moisture content and material. The reactive components are negligible in this case. A 100ohm ground rod passes the same 1.2 amps at 120 volts be it DC or AC. Even at higher voltages ohms law still limits current. Yes higher voltage pushes more current through a given resistance, but compared to a copper wire earth sucks no matter DC or AC.


Ground rods do nothing in fault clearing. On average a ground rod might pass only a fraction of 1% of current during a fault. A 0.1 ohm neutral does all the work rather than a variable electrode that can be from 20 to well over 100,000 ohms.


----------

