Size of concrete encased electrode

Status
Not open for further replies.

dfrohberg

New member
The code specifies a 4 AWG or 1/2" rebar 20 feet in length minimum for the concrete encased electrode. What if the amount of rebar is longer than 20 feet or larger than 1/2". It would seem to me that the 4AWG to the rebar connection should be larger to compensate for the larger or longer rebar in the footing. How would a person determine a proper size?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Size of concrete encased electrode

#4 is the minimum size required by the code. You can increase it if you want, but the code does not require it to ever be larger than #4.
Don

[ February 28, 2006, 10:53 AM: Message edited by: don_resqcapt19 ]
 

pierre

Senior Member
Re: Size of concrete encased electrode

Don
Ground rods are pretty much ineffective as an electrode, and generally increasing the size of the GEC to the ground rods is a waste of time and money.

With that said, do you believe the same is true for concrete encased electrodes?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: Size of concrete encased electrode

I agree with Don. The fact that an electrode is more effective at passing current to planet Earth does not mean that you need to do a better job at passing current to the electrode.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Re: Size of concrete encased electrode

It would seem to me that the 4AWG to the rebar connection should be larger to compensate for the larger or longer rebar in the footing. How would a person determine a proper size?
Are you asking about the conductor connected to the rebar? #4 is the largest size conductor required to connect to the rebar. It could be smaller based on the size of the conductors listed in 250.66. For example, a 100 amp service would only require a #8 cu conductor.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Size of concrete encased electrode

Piere,
With that said, do you believe the same is true for concrete encased electrodes?
Yes, but only because, I am not convinced that building grounding electrode systems serve any real purpose.
Don
 

peter d

Senior Member
Location
New England
Re: Size of concrete encased electrode

In my area, the CEE has not even appeared on the radar screen yet. In fact, many electricians and inspectors are still only installing/requiring one ground rod. :roll:
 

peter d

Senior Member
Location
New England
Re: Size of concrete encased electrode

Originally posted by don_resqcapt19:
Yes, but only because, I am not convinced that building grounding electrode systems serve any real purpose.
Don
But, reading that, it doesn't appear to be a great issue.

Don, could you elaborate on this?
 

pierre

Senior Member
Re: Size of concrete encased electrode

Don
One of my concerns for the function of the GE system is the purpose of keeping equipment at as close to possible "zero" potential to the earth.
Don't you think that the CEE has the best chance of doing this? Especially if the footing is electrically connected as best as possible for the perimiter of the building (keeping more of the building close to "zero" potential). I know that is idealistic, but that is what I am driving at... lofty goals for the GE system.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Re: Size of concrete encased electrode

Originally posted by don_resqcapt19:
With that said, do you believe the same is true for concrete encased electrodes?
Yes, but only because, I am not convinced that building grounding electrode systems serve any real purpose.
Let's step outside the box for a moment. Let's pretend that the grounding electrodes were used daily. Armageddon, granted, but let's pretend.

The ground rod does a cruddy job. Therefore, anything more than a #6 would be a waste of resources.

The CCE does a remarkable job. With it's low resistance, it can move a heap of current. So why restrict it's conductor?

The water pipe gets a full-size conductor, anticipating it's full use. The metal frame of a structure gets the full treatment, despite the fact that 2 of the 4 stipulations for it's use as a grounding electrode is connection to (real) other grounding electrodes.

Once again, I am confused. :)
 

pierre

Senior Member
Re: Size of concrete encased electrode

George
The CEE has great low earth contact resistance. The resistance of the earth from the building back to the transformer could be considerable. That is why I only addressed the point of "zero" potential from equipment to earth.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Size of concrete encased electrode

Pierre,
One of my concerns for the function of the GE system is the purpose of keeping equipment at as close to possible "zero" potential to the earth.
Can you explain how the groundind electrode system can do that? I don't think that it can.
Don
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Size of concrete encased electrode

Once again, I am confused.
The whole grounding subject is very confusing and I don't think that there are many who really understand it. There are too many myths and half truths out there.
Don
 

bphgravity

Senior Member
Location
Florida
Re: Size of concrete encased electrode

Since the grounding electrode system is primarily used for limiting voltages imposed by lightning, consider what is basically happening during the lightning event.

Lightning is a constant current source. No matter what the total impedance of the grounding system is, that current is the exact current that will flow through effected circuit(s). The impedance of these paths will indicate the potential imposed voltage on the conductors and equipment.

The typical lightning flash has a return stroke around 30KA. Be aware that it can be as high as 400KA. Using 30KA, if the grounding system resistance is at the magical 25-ohms, the imposed voltage will be 750,000-volts. If the the resistance is 200-ohms, the imposed voltage would be 6 million volts.

Based on this, it would appear that the better your GE system is, the lower the voltage that will be imposed on the system, and therefor that is a good thing. However, it is again bonding the makes this whole situation insignifcant. If all the systems (limited energy) and non-current carrying parts are bonded together effectively, there will be no ill-effects of this transient voltage. It bascially becomes a "bird on a wire" condition. There will be no potential between any equipment or conductors, save any weird inductive and capacitive effects of conductors in metal enclosures and insulation on conductors.

The whole system raises to the high energy state and then collapses back down to normal. Equipment not properly bonded or metallic parts near lightning energized parts may become damaged from potential flash over.
 

peter d

Senior Member
Location
New England
Re: Size of concrete encased electrode

But does the GES really provide effective protection? After all, we know that lighting is a high frequency event that does not follow the same rules as line frequency. And do we really have any effective control over the path that lightning or lightning induced current will take?
 

bphgravity

Senior Member
Location
Florida
Re: Size of concrete encased electrode

I don't believe anybody can provide concrete solid evidence either way. Research and data can be provided that seems to inidcate the GES as being effective and important. Then again, there is research and data showing absoultely no added benefit or safety provided by the GES.

This is easily the most controversial aspect of electrical theory and construction. In any case, there is way too many misconceptions about what grounding can and can't do that are positively know to be false as stated by Don.

It would do are industry alot of good to at least clear these issues up first. In the meanwhile, the code seems to provide methods and practices that are in some cases a little excessive, but have worked and been used for over 100 years. Its going to be hard to go against that history.
 

peter d

Senior Member
Location
New England
Re: Size of concrete encased electrode

Originally posted by bphgravity:
Its going to be hard to go against that history.
I agree. I'm not advocating that we do away with GES' as we know it.

What I do know, as stated Don and others, that there are many misconceptions out there which describe many things the GES cannot do. I am definitely advocating we get rid of those.
:cool:

[ March 02, 2006, 11:16 AM: Message edited by: peter d ]
 
Status
Not open for further replies.
Top