Hi to all,
Here is todays question
Regards
Gerry
yes!??
Ohm Inspector (Cockney Pronunciation), nice question Gerry, makes one think.
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…
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
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
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
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told me that an ohm is the place an Englishman angs his Hat.
Roy sr
Richard,
if you are struggling to find the answer I suggest this google search:
http://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=ground+resistance+requirements&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
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
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
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.
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…
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
This is one of the real problems that I have with the NEC and codes
In general everything works but the real issue is not that it is legal but is it a good ground
Sorry
Glad as HI we don’t have to go this deep
rlb
Richard,
Because you CAN’T…you simply can’t argue with a local AHJ about what they demand. They demand a reliable testing method to determine 25 OHMS or less or simply install the 2nd ground rod.
Now…if you are saying using a volt meter and doing OHMS is reliable to a AHJ inspector…I need to introduce you to some AHJ’s…and some very well known AHJ’s ( they help write CODE rulings)
Ok…I will take it you are not an electrical contractor…no problem but their are standards for what testing and requirements will be allowed and most AHJ’s have already set up mandates that say regardless of testing they would like (2) ground rods…now I can’t tell you why they simply say (2) and then no need to check for OHMS…it is all a matter of “SAFER” is always better with the AHJ…and 2 is always better than 1 senerio.
Also…look…while I DO care…I am a contractor and the CODE says I have to do this and that…so I do what the code says I have to do…we always drive (2) rods now…1.) because by the time I pay to spend the extra time debating it…our LARGE hammer drill can drive a ROD down in about 3 minutes…without me lifting a single sledge hammer…
I do hear ya…but in the scheme of things it takes too much time, not as accurate as the local AHJ would like as it contains to many varibles that can go wrong and in nearly 100% of the cases now the AHJ will still simply say…BUT I WANT TWO RODS…so it SHALL BE…
Also…if the building inspector comes and wants (2) rods…do you think me telling him…"Sir, I tested the one and it was fine " will make him happy.
Been Their…lol…Done…That…My Brother tries it all the time…he even has the tester ( which again you can get for about $ 180.00 )…but because the AHJ comes at different times and he is not always their…he is not going to come back to save a few bucks on a ground rod…and the AHJ’s atleast here in VA…all demand (2) rods now…so no point in testing them…
Not jumpin on ya brother…just telling you how it is in the field everyday
UPDATE- I am editing this because I wanted to place the link to the earth ground resistance test kit my brother has…he got it on e-bay for around 180.00 but I see they sell for 199.00 new anyway…
http://www.globaltestsupply.com/test_equipment/Extech_382152_Earth_Ground_Resistance_Tester_Kit.cfm
P.S…He just informed me he DID use it for a local AHJ in Nelson County and the AHJ said he still would not accept it…he MUST install the 2nd Rod…just wanted to post that for ya.
Here in the great state of WV, the three largest electricity providers REQUIRE two ground rods (1/2" copper or 5/8" copper clad) be installed within 6’ of one another. All of us who inspect electrical services for connection do not have the liability of measuring resistance to ground, because that utility companies supercede the NEC, which keeps me from being just another a–hole AHJ. Of course, the contractors find other reasons to dislike me .
10-4 Paul and Dave
When God speaks we have got to do what he says
I am still thinking about older homes where the grounding system is broke
If we SEE a problem we will note it – Just thinking and that is dangerous
If it is broke as noted in the inspection (just like an outlet) – noted and call the electrical contractor
Just thinking
I find that digging a hole looking for a ground rod INVACEIVE and too much work – I know in my heart that the rod and clamp are history but I am not going to go that far. I do note that could not find the ground rod and if I can pull the wire out of the dirt I note that it was not attached to a ground rod - safety issue
I also note if the phone and cable TV is connected to grounded
I think we are all on the same page here – IS IT SAFE??
Paul the electrical storms are so bad down here we are seeing TVSS units installed outside at the main electrical disconnect point and at the disconnect for the HVAC.
I have also seen them blown up like someone shot them with a rifle
Good grounding is a very good thing
rlb
Richard,
Since someone whom we all KNOW…must have cried and moaned about a post from EC & M online…here is the link for everyone on the 25 ohms or less story I thought you all would like…
Gesssh OLD PEOPLE…
http://www.ecmweb.com/mag/electric_cares_ohms_less/index.html