Help economical for grounding rod

D

Dongbites

Member
Location
Philippines
Occupation
Electrical Design Engineer
I want to study power system analysis to lessen the grounding rod from my different projects and also to add more credentials for every design i made, does anyone can help where i can start or what to focus to get the right calculation of it. From short circuit of the ground, settings of the time tripping of the breakers, and economical numbers of rod
 
grounding electrodes (including rods) are not installed to provide fault current of our electrical systems. they are installed to be a dump-path for static electricity to return to the earth.

equipment grounding conductors are installed to clear overcurrent devices.
 
Master Nater said:
grounding electrodes (including rods) are not installed to provide fault current of our electrical systems. they are installed to be a dump-path for static electricity to return to the earth.

equipment grounding conductors are installed to clear overcurrent devices.
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Yup i want to know how many rods should i need and to compute it
 
ok. what electrical standard are you on in the phillipines?

here, i simply install a single 8' x 5/8" rod (or other grounding electrode), attach it to the utility neutral and then use a simple ground rod tester like this ... https://www.amazon.com/ETCR-ETCR2000A-Resistance-Measurement-0-010Ω-500Ω/dp/B0FBLWFSWT/

works great every time. just had one come out to 8.6 ohms today. but i'm not in a rocky terrain.

if the electrode is under 25ohms resistance, then you're done. if it's higher than 25ohms, install another at least 6' away. then, you're done. no need for more than 2 rods, by our code book.

if you don't have access to a clamp-on tester like this, you can isolate the ground electrode and apply a known voltage to the isolated rod. take a reading of the ampacity flowing through the rod, apply it to ohms law, and you can calculate the resistance through the earth using ohms law. disclaimer: beware of electrocution hazards. but you're a design engineer, so you know what you're doing. right?

ohms law ---> resistance = voltage / amperage
 
Master Nater said:
ok. what electrical standard are you on in the phillipines?

here, i simply install a single 8' x 5/8" rod (or other grounding electrode), attach it to the utility neutral and then use a simple ground rod tester like this ... https://www.amazon.com/ETCR-ETCR2000A-Resistance-Measurement-0-010Ω-500Ω/dp/B0FBLWFSWT/

works great every time. just had one come out to 8.6 ohms today. but i'm not in a rocky terrain.

if the electrode is under 25ohms resistance, then you're done. if it's higher than 25ohms, install another at least 6' away. then, you're done. no need for more than 2 rods, by our code book.

if you don't have access to a clamp-on tester like this, you can isolate the ground electrode and apply a known voltage to the isolated rod. take a reading of the ampacity flowing through the rod, apply it to ohms law, and you can calculate the resistance through the earth using ohms law. disclaimer: beware of electrocution hazards. but you're a design engineer, so you know what you're doing. right?

ohms law ---> resistance = voltage / amperage
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Thank you sirr so much appreciated
 
Dongbites said:
Yup i want to know how many rods should i need and to compute it
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Depends what the goals are. General use one is likely fine, NEC seems to think you need to prove it is 25 ohms or less or add a second one, but doesn't require you drive any more even if you don't achieve 25 ohms with the second one. Some specific items/situations may call for lesser resistance- usually by manufacturer or designer and not by general rules of the industry. specific i
 
kwired said:
Depends what the goals are. General use one is likely fine, NEC seems to think you need to prove it is 25 ohms or less or add a second one, but doesn't require you drive any more even if you don't achieve 25 ohms with the second one. Some specific items/situations may call for lesser resistance- usually by manufacturer or designer and not by general rules of the industry. specific i
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Yup, but i saw some computation they sizes the grounding rod and they can also lessen how many rod they need to there projects, they used the actual resistivity of the soil based of soil testing from civil/geo engineers
 
There are some IEEE papers, like the Green Book for general use.

standards.ieee.org

IEEE SA Color Books (3000 Series)

IEEE 3000 Standards Collection is the family of industrial and commercial power systems standards formerly known as IEEE Color Books.
standards.ieee.org standards.ieee.org

You can get more involved with it and look at Soares "Grounding and Bonding" or some other IEEE papers on substation grounding concepts. But ultimately you should narrow down your use case and look into a IEEE for that. There are some broad concepts for grounding / earthing and then there are some VERY specific reasons to be doing it. Like lightning protection or for communication broadcasting and antennas.
 
Dongbites said:
Yup, but i saw some computation they sizes the grounding rod and they can also lessen how many rod they need to there projects, they used the actual resistivity of the soil based of soil testing from civil/geo engineers
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Grounding per the NEC for LV and MV premises installations is not the same as grounding for open air MV and HV utility yards, which are not the same as grounding to control lightning strike current on large structures.

What area are you wanting to learn about?
 
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electrofelon said:
That might be a reason for equipment grounding (although not specifically mentioned in the NEC), but they also serve a purpose for system grounding.
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i'm not sure what you are saying. do you think that "Equipment Grounding" isn't mentioned in the NEC? it sure is. they named an entire line of conductors over it. they're called Equipment Grounding Conductors. and their purpose is to provide fault current, and trip OCDs. as for the term "grounding," it just needs to stop getting used. nobody even knows what it means these days. everyone that tries to use it, ends up doing so incorrectly.

a grounding electrode's purpose is for system Earthing.

250.4(A)(1) - Electrical System Grounding - Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning (static), line surges (static), or unintentional contact with higher-voltage lines (common fault with high-voltage/low-amperage systems) and that will stabilize the voltage to earth during normal operation (equipotental plane with the earth).

not for it's own system's fault path.
 
Master Nater said:
i'm not sure what you are saying. do you think that "Equipment Grounding" isn't mentioned in the NEC? it sure is. they named an entire line of conductors over it. they're called Equipment Grounding Conductors. and their purpose is to provide fault current, and trip OCDs. as for the term "grounding," it just needs to stop getting used. nobody even knows what it means these days. everyone that tries to use it, ends up doing so incorrectly.

a grounding electrode's purpose is for system Earthing.

250.4(A)(1) - Electrical System Grounding - Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning (static), line surges (static), or unintentional contact with higher-voltage lines (common fault with high-voltage/low-amperage systems) and that will stabilize the voltage to earth during normal operation (equipotental plane with the earth).

not for it's own system's fault path.
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I meant that static is specifically not mentioned.

You don't seem to be clear on what system grounding is. It has nothing to do with equipment grounding, its completely different. Static might have something to do with equipment grounding, but has nothing to do with system grounding.
 
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electrofelon said:
I meant that static is specifically not mentioned.

You don't seem to be clear on what system grounding is. It has nothing to do with equipment grounding, its completely different. Static might have something to do with equipment grounding, but has nothing to do with system grounding.
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if not 'static,' what do you believe lightning and line surges are?

i will certainly agree. we definitely have a different concept of "grounding." it seems to me, you are confusing it with "bonding."
 
Master Nater said:
if not 'static,' what do you believe lightning and line surges are?
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I would say static is static, lightning is lightning and a line surge is a line surge.

Master Nater said:
i will certainly agree. we definitely have a different concept of "grounding." it seems to me, you are confusing it with "bonding."
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I dont think you understand what system grounding is. An electrical system can be grounded or ungrounded. Whether a system is grounded or not is just a system topology and determines the insulation levels of conductors, location of OCPDs, and how faults are handled. System grounding is intentionally connecting one conductor of the system to earth. Thats it. Connecting equipment to earth is a competely different thing.

That NEC section you quoted, 250.4(A)(1), is pretty horrible and wrong in a lot of ways. I dont see how a grounded conductor will do much to mitigate lighting or a line surge. It would help clear a fault if a MV line comes into contact with a service drop. I dont like the phrase "stabilize voltage to earth" as i think that is misleading. All it does is create a consistent potential between the grounded conductor and earth, and only during normal operation.
 
Master Nater said:
if not 'static,' what do you believe lightning and line surges are?
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While lightning is technically static discharge on a large scale, I believe the point that electrofelon is trying to make is that equipment bonding SPECIFICALLY for static dissipation of equipment is not covered in the NEC.

My main thing is: I don't believe the distinction between bonding for static dissipation vs. ground fault current path even needs to be made. If the equipment is bonded for a proper ground fault current path (as it should be), then it will also be bonded for any static dissipation requirements that may be needed due to the nature of the equipment to be used.

EXAMPLE: This would be a concern in flammable powder handling or areas with flammable vapors (i.e. bonding jumpers between lengths of stainless pipe used for pneumatically conveying bulk powders) I have personally seen this at my job where we installed what was called a "static dissipation ring". This is a 2/0, non-insulated copper conductor looped around our Class 1 Div 2 powder handling room that is attached to the building's I-beam structure at numerous points. Any non-electrical equipment (majority of it was the pneumatic conveyance piping & manual tumbler-style mixers) was bonded to this loop, since one of the powders-to-be-handled is just barely explosive enough to be worried about (if ignited in bulk or as a combustible dust cloud). This "static dissipation ring" was completely separate from the building electrical system ground. All electrical powder handling equipment was bonded as normal. This is because the ground fault current path made by bonding the electrical equipment also functions as method to dissipate static.

And line surges are not static per-se, they are just a spike in voltage from whatever the nominal line voltage is (but this COULD be caused by lightning which IS a static discharge into your electrical system, but a line surge does not necessarily always come from lightning).

electrofelon said:
I meant that static is specifically not mentioned.
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While static is not specifically mentioned in NFPA 70, it is called out in great detail in NFPA 77.
 
electrofelon said:
I would say static is static, lightning is lightning and a line surge is a line surge.


I dont think you understand what system grounding is. An electrical system can be grounded or ungrounded. Whether a system is grounded or not is just a system topology and determines the insulation levels of conductors, location of OCPDs, and how faults are handled. System grounding is intentionally connecting one conductor of the system to earth. Thats it. Connecting equipment to earth is a competely different thing.

That NEC section you quoted, 250.4(A)(1), is pretty horrible and wrong in a lot of ways. I dont see how a grounded conductor will do much to mitigate lighting or a line surge. It would help clear a fault if a MV line comes into contact with a service drop. I dont like the phrase "stabilize voltage to earth" as i think that is misleading. All it does is create a consistent potential between the grounded conductor and earth, and only during normal operation.
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it's not the NEC that is wrong. it's your ideas on what 'grounding' is.

fyi - lightning is nothing more than static on a larger scale.
 
Master Nater said:
fyi - lightning is nothing more than static on a larger scale.
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Static charge is just that, a charge. Once some threshold is exceeded actual current results and equalizes those charges though it doesn't necessarily result in total equalization, changes of impedance of the current path and charge depletion factor into when the current will stop flowing during a particular discharge event.
 
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