ECN Forum Forums General Topics of the Trade General Discussion Area Bad Ground Reading

Yes here our inspectors require #4
and make us use solid #8 on pools and tubs
unless your talkin olimpic size pools then we use the tables and that good old cad-weld
pop fizzzzzzzzz

Hi,
Thanks for the replies. Then, according to what is being said here, if it is IN a separate building ALL sub panels require a ground rod. (does that include ON a separate building or structure? If not then I digress.) If it does include ON what will you support the panel with? When you put a screw through the hole of the panel you are attaching it to a structure. Even if you mount it on unistrut or treated post it is a STRUCTURE.

Another thing, I am not clear on what you mean by the following statement "For the GEC, the NEC gives a minimum size of #6". Looking at the 2002 NEC Table 250.66 you are allowed to use #8 as the minimum for the GEC. You are not required to use anything larger than a #6 copper for a driven rod. Is that what you were talking about or did I misunderstand your statement.

Looking at Stallcups Electrical Design Book, I have to disagree with the statement that the ground rod is used soley for lightning protection. The electrical system will not function properly without it as a whole.

250.32 covers two or more buildings or structures fed from a common service. 250.50 covers the requirements.

It is a myth that electricity always seeks the least path of resistance to ground.

Thanks again for the comments.

Regards

Greg



[This message has been edited by mustangelectric (edited 01-29-2005).]

Greg
Could you elaborate on why the system will not operate properly without groundrod(s)?

Pierre

Hi,
Thanks for the reply. I am no expert on grounding but art 250.4(A)(1),(2),(3),(4) and 250.4(B)(1) points out several other purposes.

Maybe someone else out there agrees with me. It doesn't really matter I am not trying to prove anybody wrong, I was just surprised to see the statement that the ground was for lightning only. That did not sound right to me.

I agree that it is a primary component.

Grounding is probably the least understood part of the NEC.

I just do not see why a ground rod would not be required at a sub panel for a pool or hot tub but would be for a tool shed with two branch circuits.

-regards

Greg

Mustang, thanks for your patience with me!

Each building needs a ground rod. It can have more. All rods, and all panels, have to connect to it in some manner.
If you had one panel into the building, that in turn fed the other panels, then only that first panel would need to be connected to the ground rod.
If you had two feeds coming into the building, both panels would have to tie into the ground rod, Ufer, etc.

You're right about one thing, though...I got the NEC backwards as to GEC size. For NEC, #6 is "max." while our local rule is #4 "min."

Far be it for me to quibble with Stallcup, but I point out that a number of countries...Norway comes to mind...do not use ground rods, etc. Last I saw, their industry was just as modern as ours. That is- and I stress this- as long as we are talking only about the ground rod and the wire to it from the panel.
In another sense, though, it IS essential to "ground" your system; that is, have a "grounded conductor" or 'neutral'. Simply put, really weird things, including large transient voltage surges, can occur as loads change on the "hot" circuits, unless there is some point where the different feeds (transformer windings) come together.
How can this happen? Well, imagine a 240 "delta" system. Should a short happen, there would be a 208 volt to ground potential. Yet, your transformers are isolated from ground. The result of this is a wildly varying load on the windings, heat, etc. Yet, if you deliberately ground part of the delta, you can control the system, the windings can 'stabilise,' because there is a nice, clean path back to the system.
Put another way, a completely ungrounded system is esesntially a system where all loads are in "series", rather than "parallel," so changes in one load greatly affects the others.