How do you know if the grounding electrodes are good in existing buildings?

[cppoly]

When connecting to building steel or water pipe, how do you know if these are properly grounded electrodes so that you can continue to use them as such?

 

[kwired]

When connecting to building steel or water pipe, how do you know if these are properly grounded electrodes so that you can continue to use them as such?

In an existing installation, sometimes you don't know.

In a new installation you should know if there is at least 10 feet of water pipe in the ground, or how much steel is encased in concrete, in the earth, etc.

 

[ron]

Agreed with KWired.

If you want to find out, you can do a fall of potential test using IEEE 81 methods to determine earth resistivity from your existing GES

 

[mgookin]

Ohm meter?

 

[ron]

Ohm meter?

You might be able to use an ohm meter to check resistance of grounding electrode conductors from one end to the other, but it will not help you to determine if a grounding electrode or grounding electrode system is effective.

 

[K8MHZ]

When in doubt, it's always easier just to drive two ground rods and not go through all the hassle of trying to verify existing electrodes. The FOP test will only give you a resistance value, it won't tell you if the building steel or water pipe meet NEC requirements for contact distances. A water pipe with only 4 feet of metal to earth contact isn't an NEC electrode no matter how low the FOP values are.

 

[kwired]

When in doubt, it's always easier just to drive two ground rods and not go through all the hassle of trying to verify existing electrodes. The FOP test will only give you a resistance value, it won't tell you if the building steel or water pipe meet NEC requirements for contact distances. A water pipe with only 4 feet of metal to earth contact isn't an NEC electrode no matter how low the FOP values are.

But at same time "All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present" must be used - it doesn't mention testing them to see how effective they may be, other then later mentioning supplementing rod, pipe or plate electrodes that are over 25 ohms.

 

[ActionDave]

When connecting to building steel or water pipe, how do you know if these are properly grounded electrodes so that you can continue to use them as such?

I've always just done it and not worried about it. Water pipes are a bit of a worry with plastic becoming more common, never seen it used in a commercial building yet though. I never give building steel a second thought.