Ground testing building

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cornbread

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I'm hoping the esteemed group can help. Our company recently purchased a warehouse and plans to put a few production machines into the space. My question is ... how best to test the grounding for the entire building? I did a walk thru and found several grounds, but it seems woefully inadequate, just my humble opinion. We thought about just driving some additional grounds but I really would like to get a base line number to make sure we are improving the situation. Any thoughts or suggestion are appreciated.
 
cornbread said:
I'm hoping the esteemed group can help. Our company recently purchased a warehouse and plans to put a few production machines into the space. My question is ... how best to test the grounding for the entire building? I did a walk thru and found several grounds, but it seems woefully inadequate, just my humble opinion. We thought about just driving some additional grounds but I really would like to get a base line number to make sure we are improving the situation. Any thoughts or suggestion are appreciated.
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I would look at article 250 and see if the existing grounding electrode system is in compliance with the requirements found there. If it is in compliance, and in good condition, there is no good reason to go any further.

To be candid, people worry way too much about "grounding". It just does not do all that much for you, nor does it solve any problems. It is not even really a safety issue.

Bonding, on the other hand, is a safety issue but is completely a separate issue from "grounding".

I also echo the other posters comment about jack leg neutrals.
 
Appreciate the replies. I'm use to new installations where we ground everything. Will take a look at 250 and see where that leads.
 
What are your concerns?

Resistance of the grounding electrode system?

Connection to Earth?

Or ground resistance between equipment and the MBJ?
 
This is a high warehouse and I can find only two grounds... I'm sure there are more but they may be buried. The warehouse has 4 0r 5 2000 KVA transformer feeding it.. 13.8 KV to 480V. My concern is we are staring to install production equipment and I want to make sure we have a good grounding for personnel /perator safety.
 
cornbread said:
This is a high warehouse and I can find only two grounds... I'm sure there are more but they may be buried. The warehouse has 4 0r 5 2000 KVA transformer feeding it.. 13.8 KV to 480V. My concern is we are staring to install production equipment and I want to make sure we have a good grounding for personnel /perator safety.
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what two grounds have you found? part of the problem is terminology. All of the grounding electrodes that are present have to be connected together and connected to the electrical system. But this can be a single wire that starts at the service point and works its way to both grounding electrodes.

250.52 tells you what things are considered grounding electrodes.

a 2000 kva xfmr at 480V would be about 2400 Amps. A feeder or service that big would require ground fault protection. That is a lot of juice for a warehouse.

In any case, actual grounding does not really do much for safety. This is what the code says about why electrical systems are grounded.

Electrical System Grounding. Electrical systems that are
grounded shall be connected to earth in a manner that will
limit the voltage imposed by lightning, line surges, or unintentional
contact with higher-voltage lines and that will stabilize
the voltage to earth during normal operation.
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Tony S said:
Have a read of this. http://www.fluke.com/fluke/inen/solutions/earthground/Fall-of-Potential.htm
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Tony, That test is a 3-point test for verifying the resistance to Earth of your electrode system.

What I would do is verify that there is a common electrode system.
Verify the XO termination is properly bonded at his transformers and verify all services are properly bonded.
If there are existing feeders I would megger the feeders to include the neutral to ground.
They could perform a two-point test between distribution equipment and the main ground or main service but in most buildings, you will find due to all metallic components (rebar, structural steel, ducts, water pipes and the like) the impedance is low.
 
Grounding is not important for personnel safety, bonding is. Grounding provides protection from lightning. Bonding all metallic raceways, boxes, panels, receptacles provides a path back to the source (panel) for fault current to open the circuit breaker.
Put your efforts into making sure all the bonding is correct. Metal columns need to be bonded.
And, just as important as bonding, is GFCI protection. Outside receptacles, within 6 ft of a sink, wet locations, concrete floors, need GFCI protection
 
Appreciate the replies. After some more research we are going to do a fall of potential test, visual inspection, static bonding review and some continuity test. Hopefully this will give us the info needed to conclude the grounding in adequate.
 
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