inverse disagreement with inspector

Status
Not open for further replies.

cschmid

Senior Member
ground rod beat to death..has anyone ever used screw together rods?? ground rods serve only to protect high voltage surges and to stabilize the the transformer..but from personal experience the rods are necessary to be at 25 ohms or as close as possible to stabilize a system..I had an apartment building with 5 panels and blowing bulbs every other week..the apartment managers were changing the commons every 12 to 14 days..owner weant far as to by bulbs by the case and gave to residents the ohms to ground were over 150 it took three screw together rods to get down under 25 ohms..I cant not explain it in engineer terms but they now change the commons once a years on a 24/7 burn..no more tenants saying the electrical system was the cause of the electronic equipment being fried..But I will do some research on the stabilization thing unless someone here will explain it for me..
 

sticko

Member
Location
nothern virginia
Tori said:
I remember doing a job in the capital for the visitors center - that albatross of your money
testing was required for grnd rods - there was a drought at the time - 13 ground rods later and still had'nt passed


Dosen't Nec 250-56 say that when 25 ohms is not achieved on the first rod, then one additional rod is added? Not to keep installing rod after rod until you get 25 or lesss ohms.
 

lpelectric

Senior Member
There are a few installers around this upstate area that have taken the notion that burying 2 ground rods 2 feet deep laying horizontally in a ditch and spaced 6 feet apart is easier than driving the rods. They want this to become the accepted norm and balk at the suggestion of driving the rods perpendicularly to a full 8 foot depth. :smile:
 

haskindm

Senior Member
Location
Maryland
The 2nd ground rod does add to the safety of an installation, and so would the 3rd, and 4th, and 1999th, by lowering the resistance to earth in the event of a high voltage event and lowering the potential to ground in the event of a lost neutral. Mike Holt has a video of him driving 2 50' ground rods at his property and comparing the voltage to ground with one and with two rods and no POCO Neutral. It is an excellent learning tool. The question is when is enough, enough? The NEC has determined that two is enough unless you can demonstrate that you have 25 ohms resistance or less with only one. By the way, he never lowered the resistance enough to trip a breaker.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
sticko said:
Doesn't Nec 250-56 say that when 25 ohms is not achieved on the first rod, then one additional rod is added? Not to keep installing rod after rod until you get 25 or lesss ohms.
Correct. I believe that the only reason for requiring one additional rod is that the code makers could not justify a rule that said to "keep adding rods until you hit 25 ohms." They could never prove with math or science that in all possible situations a third rod would be sufficient, or that a fourth rod would still not be sufficient. But a rule that says to add one more is easy for the user to accept.

Several of you have said that you simply add the second rod and call it a day. Did it occur to you that the code making panel did exactly the same thing (i.e., let's just require one more and call it a day)?

(ASIDE: I have no facts to back up my statements about the thought process used by the CMPs. I am only describing what makes sense to me.)
 

billsnuff

Senior Member
did a rural residence upgrade this last year. manufactured home with 60A being replaced with modular home with 200A. POCO needed to upgrade transformer, supplied new meter pan (bond neutral and gnd there) and had to have a 200a disco one pole. underground with thwn in PVC , 3 wire with gnd to subpanel in house (no bonding jumper). There already existed a gnd rod at the transformer pole and one and the meter pole. they were about 150' apart. POCO says you already have two, you don't need any at the house. No inspections hear until next year.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
cschmid,
but from personal experience the rods are necessary to be at 25 ohms or as close as possible to stabilize a system..I had an apartment building with 5 panels and blowing bulbs every other week..the apartment managers were changing the commons every 12 to 14 days..owner weant far as to by bulbs by the case and gave to residents the ohms to ground were over 150 it took three screw together rods to get down under 25 ohms..
All you really did is to provide a better path for the grounded conductor current because the service grounded conductor has an impedance higher than it should have. This problem would have also gone away if some one would have repaired the service grounded conductor.
Don
 

cschmid

Senior Member
Don I did check the neutral for size and the connections..i even had the POCO come out and open up the trans former..we monitored the phase voltages and every thing..So can you explain a little more on your theory for me..I might even like some of the math on it..I am always wanting to learn something..I would hate to go though a day and not learn something it would almost be a wasted day..but a little rum and coke you have wasted night..:grin: :D
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
cschmid,
I don't have any math, but the load does not see the line or grounded conductor to earth voltage, it only sees the line to grounded conductor voltage and that doesn't change no matter how many ground rods you install assuming that there are no problems with the system. Now if there is a poor connection or some other reason for a higher than normal impedance on the grounded conductor, you can see high and low voltages at the equipment that is connected line to grounded conductor. (the classic open neutral problems on a multiwire circuit and the service is a multiwire circuit) In that case, additional ground rods or longer ones will act to lower the impedance of the grounded conductor and in some (rare) cases may be enough to make the problem go away.
Don
 

cschmid

Senior Member
okay just for reference the area I am talking about is all sand..Now I have always had the understanding that the system would function without a ground and that the circuit was from the conductor back to the center point tap or from winding to winding..but the transformer primary can have up to ten percent voltage variation either side of of the rated voltage..I thought the Ground was to stabilize the transformer primary voltage swings and to protect from high voltage spikes..let say for example you have a 480 volt primary and your voltage can swing ten percent that is 48 volt swing now on the secondary it will also vary 10 percent..but the primary can swing more rapidly than the secondary and that can make the secondary voltage unstable as well..So is my understanding skewed..
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
ALL we are doing is helping the poco,Nothing will ever fix it.On our end at best we help reduce a lightning strike.25 ohms to ground is a joke,who came up with that number and just what did he/she think that solves. Do the math and 25 ohms wont do nothing to remove a fault.We been had and fixed nothing.When will they wake up to reality ?A stupid piece of steel ,copper or even gold can not clear a short.
 
Okay, I will ask the question again.

One installs a ground rod, he does not want to test it so he drives another everyone is happy...this I understand.
Lemmings follow the leader without question and jump off of cliffs...


My question is this.
Why are we driving a second rod? Does it really make the installation safer?
If there is no definitive answer that it is safer, why has it become part of the code?
If someone telling me it is safer, then please tell me why it is safer, not just that it is.


Take lightning out of the equation, as in most areas of the country lightning is not a factor.
 

tonyou812

Senior Member
Location
North New Jersey
I just put two and call it a day myself. No reason to get your knickers in a twist about. Im not sure what the test cost but it almost seems like a lucrative situation. What if you had a side buisness of testing ground rods for less than it cost for an extra ground rod and the time it will take to drive in the present situation.
 

domnic

Senior Member
Occupation
Electrical Contractor
grounds

grounds

whillis said:
Code is a minimum, and when it comes to a good ground a little extra effort never hurts.
how many oms is a good ground.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
Pierre C Belarge said:
Okay, I will ask the question again.

One installs a ground rod, he does not want to test it so he drives another everyone is happy...this I understand.
Lemmings follow the leader without question and jump off of cliffs...


My question is this.
Why are we driving a second rod? Does it really make the installation safer?
If there is no definitive answer that it is safer, why has it become part of the code?
If someone telling me it is safer, then please tell me why it is safer, not just that it is.


Take lightning out of the equation, as in most areas of the country lightning is not a factor.


Thats easy.They sell twice as many clamps and rods.That is likely why it made it in the nec.They did give us a choice.
 
Status
Not open for further replies.
Top