QOD for 04/11/2006

[gbeaumont]

Hi to all,

Here is todays question

Regards

Gerry

[pkelley]

yes!??

[Brian E. Kelly]

Ohm Inspector (Cockney Pronunciation), nice question Gerry, makes one think.

[Paul W. Abernathy]

lol.....Guys this just happens to be one of the things we teach on the 1st week of Residential Electrical Training.....This is one that you wont test....you wont understand...BUT you must comply with otherwise you have to PROVE your job complies......

Good question Gerry.....I am a bit sad to see very few....are getting it right......resistance..OHMS....think first guys...THINK....

[Leonard E. Ungar]

Hi! Paul;
You beat me to it, I was just going to say to Gerry that we do not check for that during an inspection that is beyond our scope correct ????

Regards Len

[gbeaumont]

Hi Len,

yes it is beyond the scope of what a home inspector should be checking, but not beyond what a home inspector should know.

I often ask questions that I hope reinforce concepts behind systems and hopefully get a few people thinking.

This question is a case on point as it is fundamental to the effective grounding of electrical systems.

Regards

Gerry

[Richard L. Bennett]

Gerry

Who's spec???? NEC???

Don't even know the Google search specs to use

I think you will check there is no NEC spec just a recommendation and if not met "drive one more ground rod"

If there is a spec I would like some one to test for it down here in sandy Florida and then require JOE builder to meet it

We are a high lighting area

rlb

[Roy D. Cooke, Sr]

Gerry Beaumont vbmenu_register("postmenu_41321", true);
Gerry Beaumont Consulting
Education Committee Member

told me that an ohm is the place an Englishman angs his Hat.
Roy sr

[gbeaumont]

Originally Posted by rbennett

Gerry

Who's spec???? NEC???

Don't even know the Google search specs to use

I think you will check there is no NEC spec just a recommendation and if not met "drive one more ground rod"

If there is a spec I would like some one to test for it down here in sandy Florida and then require JOE builder to meet it

We are a high lighting area

rlb

Richard,

if you are struggling to find the answer I suggest this google search:

http://www.google.com/search?hl=en&l...ts&btnG=Search

Hope it helps

BTW your lightening question also points to the reason that Ufer grounds are so common down here, sandy soils not withstanding.

Regards

Gerry

[Richard L. Bennett]

Ok

My answer is 25 ohms because no one knows how to do the measure the ground resistance and the 5 ohms spec is hard to achieve in most areas

My home is 3.7 ohms measured by ME --- SIX ground rods and one in the septank ---(Now I know where it is)

Total cost $42.00 -- 10 of the rods were free -- Wire was free - labor - clamps etc. I had to buy last year -- sand down here is like a large insulator

rlb

[gbeaumont]

Originally Posted by rbennett

Ok

My answer is 25 ohms because no one knows how to do the measure the ground resistance and the 5 ohms spec is hard to achieve in most areas

My home is 3.7 ohms measured by ME --- SIX ground rods and one in the septank ---(Now I know where it is)

Total cost $42.00 -- 10 of the rods were free -- Wire was free - labor - clamps etc. I had to buy last year -- sand down here is like a large insulator

rlb

Thanks Richard,

see, it wasn't that hard, all it needed was a little application.

Monday morning quarter backing is easy, actually doing anything knowing full well that you will be constantly challenged is, well, challenging.

BTW, if you feel like explaining my Ufer ground comment in dry climates, be my guest, I could use the help.

Regards

Gerry

[Richard L. Bennett]

Gerry

I am sorry - public crow eating here -- One of the big rules on QOD is NOT give what one thinks or knows as the answer. I apologize

Ufer grounding for me not an option - my home is not built on a slab

As far as explaining it here is about all that I know

If one can get enough contact with something the resistance keeps going down. More rods - longer rods - Many conductors placed just under the surface of the ground - digging a hole and filling it with old cars and then filling it back up. In short get as good as a contact as possible with mother earth.

As I understand Ufer grounds it is making use of the concrete reinforcing rods that are in the concrete slab on the Florida Slab on Grade homes. This gives a lot of surface area to the concrete which has a large surface area to the ground. Even know concrete is not a good conductor if you get in contact with enough concrete you have a pretty good ground.

While grounding is very important how it is done and is it done correctly esp. here in Florida is a big issue -- mainly because it is very seldom tested by any one.

Now is the time for some one to check in here with an correct any errors so we don't get bad information out to everyone

Once again Gerry I apologize

rlb

[Doug Edwards, CMI]

Probably 75-80% of the homes I inspect have the wrong type clamp (Weaver) on the ground rod, it is always either loose because it can not tightened any further (because it is not the right clamp or they installed it improperly) or the alloy clamp is not longer even there, it has corroded away to nothing or just bits and pieces left behind. I have found many to have no ground rod at all, just the grounding conductor stuck down straight into the ground. Grounding and bonding seems to be an area that even some of our local electricians find confusing. Not all but too many just take a short cut figuring no one will ever notice.

[Paul W. Abernathy]

Originally Posted by rbennett

Gerry

Who's spec???? NEC???

Don't even know the Google search specs to use

I think you will check there is no NEC spec just a recommendation and if not met "drive one more ground rod"

If there is a spec I would like some one to test for it down here in sandy Florida and then require JOE builder to meet it

We are a high lighting area

rlb

Actually the NEC states : A single electrode consisting of a rod, pipe or plate that does not have a resistance to ground of 25 ohms or less SHALL BE augmented by one additional electrode or any of the types specified by Art 250.52(A)(2) through (A)(7).

Now......here is the thing and why it is a great learning question by Gerry.....I as the contractor have to PROVE to the AHJ that it is 25 ohms or less...as I have been down that road a few times with my stubborn brother who would like to fight it sometimes and show a single rod is 25 OHMS or less...but why fight it...just drive the 2nd one......Now the NEC does not say at that POINT you have to then again test it to get 25 or less....driving the 2nd one meets the requirement......this is why most AHJ's will now just demand (2) ground rods....( ie: if ground rods are being used of course )

Like I said...you wont test it...BUT you should know it because a buyer may ask something about it.....knoweldge is good....saying we dont have to learn it because we dont inspect it is not good...

[Richard L. Bennett]

Paul

Why not test the single rod when it is placed in the ground and tell the building inspector good based on you testing on day one??

It is cheap to make the test at that time because power is not turned on to the home etc.

And if the #2 ground rod is legal but does not meet good grounding why not note it and help the builder do it right

Just some thoughts

rlb