Ground Loop

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ItsHot

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I am in the middle of a job that the plan calls for me to locate outside of a building the "ground loop". Then install a isolated grounding conductor from this sensitive piece of equipment to the ground loop. My question(s) Normally is the ground loop for roof-top lightning arrest system? If the equipment requires an isolated ground you have to have a separate isolated ground system.(?) I think the need for an isolated ground is why they are asking to locate "ground loop"?? Can you ground to a lightning systems ground???
 
All grounding electrode systems need to be connected together. Ideally there may be a common point where all electrodes are connected. In my experience this is seldom the case.

Lastly a truly isolated ground does not exist, one it is a NEC violation and two EMT, HVAC ducts, water pipes, metal studs, re-bar, structural steel, all come in contact with the equipment at some point it is inevitable.

Believe me I have seen some HOODOO VOODOO (my terminology not the designers) done in the name of an IG ground system and something always defeats the good though mis-guided intentions.
 
ItsHot said:
I am in the middle of a job that the plan calls for me to locate outside of a building the "ground loop". Then install a isolated grounding conductor from this sensitive piece of equipment to the ground loop. My question(s) Normally is the ground loop for roof-top lightning arrest system? If the equipment requires an isolated ground you have to have a separate isolated ground system.(?) I think the need for an isolated ground is why they are asking to locate "ground loop"?? Can you ground to a lightning systems ground???[/quote]

This is a good question. I do not believe you can "ground" to the lightning system, even though the lightning system is required to be bonded to the buildings grounding system.
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Not saying you can or can not but where in the NEC* does it tell us these electrodes should be bonded together?

* I have not checked NFPA 780 but will.
 
Thank You

Thank You

Thanks guys, I need to do a liitle "homework" on this before getting back to it! I always thought the "ground loop was isolated from the grounding system because it is there to take on electrical strikes via the rooftop electrodes?? With the specs calling to ground a half-million dollar piece of equipment to this outside ground loop, I hope the engineers have this one right!!!
 
brian john said:
Not saying you can or can not but where in the NEC* does it tell us these electrodes should be bonded together?

* I have not checked NFPA 780 but will.
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250.106 of the NEC.

And see 250.60 for additional details...
 
yes it says it must be bonded 250.106.. but if the EE has designed it differently would you not need to follow there direaction since it is their design?..Yet the NEC does not give exception..
 
cschmid said:
yes it says it must be bonded 250.106.. but if the EE has designed it differently would you not need to follow there direaction since it is their design?..Yet the NEC does not give exception..
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IMO, you can't get around 250.4(A)(3) and (4)

The equipment that has the isolated ground still must be connected back to the source of the supply. If that supply is on a different ground system, the ground systems end up being connected.
 
cschmid said:
yes it says it must be bonded 250.106.. but if the EE has designed it differently would you not need to follow there direaction since it is their design?..Yet the NEC does not give exception..
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All the contracts we get say we must follow all applicable codes.

Without written spacial permission from the AHJ the EE can not overrule the NEC.
 
I agree with it being bonded..yet you see through out the code exceptions regarding with engineers supervision and bob would beable to site the areas better then I for memory..Yet I have not seen that in any area of the grounding section that I can remember..So if the Engineer designs it and the code states different who is responsible for the modification? or should the contractor get in touch with the engineer and let the engineer make the change?
 
brian john said:
* I have not checked NFPA 780 but will.
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Here's what I found in 780-

4.14.1 General. All grounding media in or on a structure shall be interconnected to provide a common ground potential.
4.14.1.1 This interconnection shall include lightning protection, electric service, telephone, and antenna system grounds, as well as underground metallic piping systems.

Also 4.14.2 covers bonding to the metal water pipe.
 
iwire said:
All the contracts we get say we must follow all applicable codes.

Without written spacial permission from the AHJ the EE can not overrule the NEC.
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As Bob has stated here, an EE is not permitted to design outside of the NEC requirements unless he has consulted and received written permission. As with any other person, EEs are bound to the codes.
 
Think about it; all grounding systems have to bond together and if there is neutral/stay current form grounded conductor parallel path (due to common ground at service disconnect and serving transformer) then isolating will NOT keep current off the bonding [EGC?s]. I think (especially in new construction) the stray current does not enter the bonding through branch as much as it does through the ground system bonds and we certainly should not settle for unsafe circuitry that intentionally installs current on the bonding.

With all this said why isolated ground?
 
So the question remains where would you bond all the electrode systems. Me personally I feel it is best if this happens at one point, such as a Master Ground Bus then out to utility water pipe, to the LPS ground ring, service driven electrodes, any SPECIALITY electrodes driven for a variety of reasons.
 
ItsHot said:
I am in the middle of a job that the plan calls for me to locate outside of a building the "ground loop". Then install a isolated grounding conductor from this sensitive piece of equipment to the ground loop. My question(s) Normally is the ground loop for roof-top lightning arrest system? If the equipment requires an isolated ground you have to have a separate isolated ground system.(?) I think the need for an isolated ground is why they are asking to locate "ground loop"?? Can you ground to a lightning systems ground???
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I would suggest that the ground loop being referenced is the underground bare copper 4/0 or larger that building steel and the electrical system are tied to.
JM
 
cschmid said:
So if the Engineer designs it and the code states different who is responsible for the modification? or should the contractor get in touch with the engineer and let the engineer make the change?
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I believe both the engineer and the EC will be pulled into any problem that might occur down the road. In this case, I would send a letter to the engineer with your design concerns listing the NEC articles that you believe are being overlooked. Of course you want to try to word the letter in a friendly non-threating way.

You could always ask the AHJ (but I would go to the EE first).

Whatever you do, get responses in writing for your job file!
 
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