UFER Grounding scheme

M

Mumbaigirl

Member
Location
USA
Occupation
Electrical Engineer
We are installing some new equipment and it will be housed in a shipping container (of sorts). The equipment will be fed from 480V feed from a nearby MCC. We are putting in a new pad for this and I wanted to know the grounding scheme I am attaching can be considered an UFER ground per article 250.52. I would greatly appreciate some input on this.

1748978488183.png
 
Yup, bottom of the footing, probably worth having a sectional view so that it's clear the CEE is at the bottom of your footing. Does your pad design have a footing and use steel reinforcement?
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That second detail is probably overkill, but sometimes you need/want overkill, such as in high seismic areas. I just grabbed those off the internet, I'm not sure what kind of projects they are for.
 
Thank you so much! I appreciate this. I have asked that question to our civil engineer. In case. they come back and say the pad design doesn't include a footing, would adding ground rods on opposite corners work? Thank you again for the help!
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Your first image had a note "bonded to existing plant ring", what's that? Depending on many variables, that bonding alone may be enough.
 
Multiple grounding points in a system can set up a potential for voltage gradient in the event of nearby lightning strikes. Notice, I didn't say they weren't allowed, just that they're generally not a good thing, unless they are part of the same Grounding Electrode System.

 
Joe.B said:
Multiple grounding points in a system can set up a potential for voltage gradient in the event of nearby lightning strikes. Notice, I didn't say they weren't allowed, just that they're generally not a good thing, unless they are part of the same Grounding Electrode System.

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For this application, I would assume that the multiple ground rods will be tied together. If there are no other electrodes, the code will require two or permit testing to prove one is 25 ohms or less.
 
don_resqcapt19 said:
For this application, I would assume that the multiple ground rods will be tied together. If there are no other electrodes, the code will require two or permit testing to prove one is 25 ohms or less.
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I agree, and I would have made that assumption as well, but the way it's shown on that second drawing made me wonder...
 
Thank you all so much!

The answer from the civil folks is: The foundation is a rectangular block of concrete with reinforcing steel. It's approx. 4" above grade and 3'-6" below which is in direct contact with the earth. If that's that case, will the first scheme work as the rebar can be counted as a CEE? I am not showing any additional ground rods here.

Do I still need an additional ground rod in this situation to ensure that the resistance is less than 25 ohms? I read online that "a single rod, pipe, or plate electrode (including the CEE) may need to be supplemented if it cannot demonstrate a resistance to earth of 25 ohms or less".
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3.5' deep sounds like a footing to me, especially if it's poured in place.

An Ufer ground requires no other electrodes, regardless of resistance.
 
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