stray current

Status
Not open for further replies.
I have a ground rod that is reading 121 ohms using a clamp on meter. As high as that is it sounds to me like a faulty reading. Only one reading was taken. Any input? Also is there any standard or acceptable range of stray current? Reading 157mA on an underground water pipe and 3.625mA on cold water and 2.175mA on hot water at the water heater. The underground water pipe is one that was replaced due to holes in the original pipe.
 
mistermajestic4@msn.com said:
I have a ground rod that is reading 121 ohms using a clamp on meter. As high as that is it sounds to me like a faulty reading.
Do you mean to say 121 amps of stray current, or 121 ohms of resistance to earth? That sounds pretty good for an ohm reading on a ground rod.

Are the other readings milliamp readings or amp readings? If milliamps, that's next to nothing at all for a service, IMO.
 
If the UG water pipe is continuous there will always be current on it, back to the transformer or next door. 121 MA is not much, but look for DC current. AC current does not cause corrosion, its DC. The best solution and recommended by the AWWA is to install a 6" length of plastic pipe 15 ft from the building, to keep the water pipe as a GE.
 
mistermajestic4@msn.com said:
The 121 is ohms of resistance, much higher than the 25 ohms allowed by code.
In discussions about the 25 ohm requirement, I believe it's been in there for a very long time, so most likely it was in the code at the initial installation of the service (far out guess).

So, if you need to bring this service up to code, drive a second ground rod over six feet away and call it a day. The resistance reading after the second rod does not matter. If it winds up having an overall resistance for the pair at 60 ohms (or inexplicably 600 Ω), it's compliant.
 
So, if you need to bring this service up to code, drive a second ground rod over six feet away and call it a day. The resistance reading after the second rod does not matter. If it winds up having an overall resistance for the pair at 60 ohms (or inexplicably 600 Ω), it's compliant.

Should the ground rods be bonded to eliminate step potential?
 
Chad Fabry said:
That's why I asked. Every schematic I've seen shows a bonding jumper rod to rod outside the structure.

It's up to the installer.

You could run a separate GEC from each rod to the service or you could run one GEC from panel to rod and place a jumper between the rods.
 
you also must use separate lugs for the wires from rod to rod or you must use a continuous wire from the second ground rod to the first rod and then to the panel..I don not believe you can run separate wires from two separate rods to the panel? correct me if I am wrong here..
 
If you also check the Ph of the water, that can sometimes be more revealing than any amp reading you'll ever take related to pinholes in copper pipe. The word among plumbers is that many municipal water supplies are more caustic since 9/11, which will help prolong the pipe's life, but many private wells can have very acidic water.

EDIT: http://www.plumbingworld.com/cuno_info_page.html
 
Last edited:
As Bob has explained, there are multiple ways to install the ground rods. The ground rods are generally driven to "supplement" the cold water - 250.53(D)(2).
There may be instances when the rods are "the" electrode system as per 250.50, but that is not too often the case.
 
Pierre C Belarge said:
As Bob has explained, there are multiple ways to install the ground rods. The ground rods are generally driven to "supplement" the cold water - 250.53(D)(2).
There may be instances when the rods are "the" electrode system as per 250.50, but that is not too often the case.


Yeah, like around here where city water is actually a pipe dream... :grin:
 
Last edited:
cschmid said:
I don not believe you can run separate wires from two separate rods to the panel?

The NEC allows that, some local inspectors might have an issue with it for unexplainable reasons.
 
Status
Not open for further replies.
Top