I have a ufer subbed out in a residential basement , outside I have added a supplemental grounding rod and run a continuous #6 GEC from the service panel neutral terminal connecting them together.
Also I have bonded the well casing and water pipes continuous with #6 back to the service panel and terminated it on the neutral bar.
Should I have done this different and run the water pipe GEC back to the Ufer??
If all the conductors to the individual items are sized appropriately (per 250.66) your installation sounds fine, that is if I understand you correctly.
Is the well pipe copper, galv? Typically I ground the well pipe at nearest point and use to rods. The well lines are usally plastic and the house lines are not in the earth even if they are metal. I never have failed an inspection with this setup.
I guess your question is beyond what I do when installing a GEC to a system , I simply use table 250.66 and go from there . How do you size the GEC with your calculations?
Re: Grounding question residential#72842 12/12/0610:45 AM12/12/0610:45 AM
I do it the hard way. Especially in commercial, where we often use parallel sets of conductors for a lateral service. Find the cross-sectional area times how many parallel runs (say, 6 * 600 kcm) and whatever that equivalent is, you can find it in 250.66. 1100 kcm is the largest size listed with 3/0 for a GEC. If the total equivalent size is over 1100 kcm, you can size the GEC at 12.5% of the hot. Say, the total was greater than the cross-sectional area of 1100. Find 12.5 % of that and use the table to find what wire size matches that figure and that's your GEC.
Around here, in a house, cities want nothing less than #4 for cold water ground and you can use #6 ground to a ground rod or UFER for a typical 200 amp service. Some cities require at least a 5/8 ground rod, I normally just buy a 3/4. That never fails inspection.
Also, all bonding must take place at the first means of disconnect, whether that is a disconnect switch or the panel itself. That means that all grounding conductors meet at the point where neutral is bonded to ground. This is to insure an effect ground fault current path that allows a grounding current to find it's way back to neutral, back through the feeding transformer and back through the suppling breaker at a high enough current to make it trip. Otherwise, the breaker wouldn't trip and something or someone would continue to get electrocuted and the effect of grounding thing to another rather than back that system bonding point creates alternate paths for ground fault current, sometimes referred to as a ground loop.
[This message has been edited by rws (edited 12-12-2006).]
