Checking ground system on 20 story building.

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SmithBuilt

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Foothills of NC
I'm bidding a job that requires and I quote.

"Check ground system with "earth megger". Furnish the test result to owner and engineer. The readings shall be 25 ohms or less."

This is a 20 story building. I'm only to install a sub panel fed by a main panel for this floor which is fed by a bus duct. I can understand checking my work to the floor panel, but I don't see how I can include in my bid a guarantee that the existing grounding system is 25 ohms or less.

How would I even check the whole system? I assume the building steel and incoming water line are probably the grounds for the building. There's concrete and pavement all around the building with the exception of a small flower garden that may even have a concrete bottom.
 
SmithBuilt said:
I'm bidding a job that requires and I quote.

"Check ground system with "earth megger". Furnish the test result to owner and engineer. The readings shall be 25 ohms or less."
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What are they wanting you to bid?

Testing only, or testing and repairs?


The statement "readings shall be 25 ohms or less" makes me wonder if they want something done if they test over 25 ohms?


EDIT... perhaps this is a spec for new work, and they want you to submit test results that your new work is less than 25 ohms?

RFI them and tell them that no such thing as an earth megger exists. :)
 
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mdshunk said:
What are they wanting you to bid?
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This is an up fit for an office with lots of data processing equipment.

mdshunk said:
The statement "readings shall be 25 ohms or less" makes me wonder if they want something done if they test over 25 ohms?
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I'm certain.

mdshunk said:
RFI them and tell them that no such thing as an earth megger exists. :)
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Electrical Engineer plans, I have left him a message.
 
This is a common spec from STRICTLY MY OPINION from people they do not know what they want or need.

Ask them what the need or why.

Where do they want the 25 OHMS? at the panel.

Is this a new Separately derived system (does not sound like it).

Normally in a building this size in with a massive slab contact with the earth with all the multiple paths it is:

hard to imagine it is not somewhere near 25 ohms (Depending on location).

Hard to impossible to test, A 3-point test requires shutting down the building and going out 10 times the diagonal of the electrode system. A clamp on tester would show an error because the chance of a GROUND LOOP is is almost certain in a building of this size.

So in conclusion WHY? and HOW?

They will tell you that the last company had no problem meeting the spec..YEAH Sure.
 
I'm still waiting on them to return my call.

If they do not return my call I will include in the bid that I will guarantee what I install to be compliant. From floor panel to sub panel and outlets. Beyond that will be by the hour.

Not a separate system.

Tim
 
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