I am working on a industrial facility that has 2500KVA, 12.7KV-480/277V service. In the past I have always specified a triad ground rod system at a service entrance. The triad ground rod system has been based on utility requirements and best engineering practices. The utility at this site does not require a redundant ground. Are there any codes or standards that I could reference to back up the use of a triad ground rod system at a service entrance.
Triad requirements for a Industrial Service entrance.
- Thread starter cukele
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Will you be using a CEE?
- Location
- Bremerton, Washington
Not in the NEC. The usefulness of a triad ground is doubtful, are you in a area with a lot of lightning?
A ufer ground may be required, is far more effective at essentially no cost.
A ufer ground may be required, is far more effective at essentially no cost.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Any particular reason why you won't be using a CEE? No rebar that meets the CEE requirement?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
best engineering practices???
According to who?
In any case, ground rods don't make very good grounding electrodes, no matter how many you put in.
I honestly didn’t think that was a real thing…
What utility requires it?
I’m assuming three rods minimum 10’ apart? Maybe it’s one of those holdover things sort of like an old wives tale…
what if you don’t have that much area?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Triad=hogwash. Pouring some snake oil on the ground will probably lower electrode resistance more.....
And I thought they were a criminal gang...................
You should get out more!
Not you
"Triad grounding is important in order to facilitate periodic testing of the effective grounding system. Three rods are buried and connected with insulated cable (probably 90 mm), of course the insulation of that part of the cable which is bolted to the rod is removed. Test pits allowing access to the top of each rod.
In order to effectively test the ground resistance the rest of the grounding system must be disconnected from the rod, if only a single rod was buried then for the duration of the test the system would be ungrounded which is extremely dangerous, the three rods and their interconnections allow this testing to occur and also eliminate the need for a test rod to be driven as 2 out of the 3 rods can be disconnected and the earth resistance test done while the third rod maintains an effective ground. The distance between the rods is usually equal to or a bit more than the length of the rod in order to avoid interference and thus provide a true measurement of the earth resistance at that point. This system also facilitates redundancy and increased availability of the grounding system and is used mainly for grounding of instrumentation and computerized systems and so is isolated (except for a single bond) from the plant (dirty) earthing network which may be buried bare copper, rods and building rebar etc."
In order to effectively test the ground resistance the rest of the grounding system must be disconnected from the rod, if only a single rod was buried then for the duration of the test the system would be ungrounded which is extremely dangerous, the three rods and their interconnections allow this testing to occur and also eliminate the need for a test rod to be driven as 2 out of the 3 rods can be disconnected and the earth resistance test done while the third rod maintains an effective ground. The distance between the rods is usually equal to or a bit more than the length of the rod in order to avoid interference and thus provide a true measurement of the earth resistance at that point. This system also facilitates redundancy and increased availability of the grounding system and is used mainly for grounding of instrumentation and computerized systems and so is isolated (except for a single bond) from the plant (dirty) earthing network which may be buried bare copper, rods and building rebar etc."
Waste of time and materials. It's no more effective then a cone shaped tin foil hat. I have three point FOP tested many (always required by a design engineer) and it made little difference when I removed two from the triad and tested a single rod.
Roger
Roger
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
a) please cite the source for that
b) does not look like North American; not that electrons behave differently on other continents, but practices differ
c) if you don't need to test the grounding system, and many don't need it, testability isn't relevant
d) if you do need to test, it's generally not that difficult to add one specifically for the purpose
e) if you have & use other qualifying electrodes, you don't need a "triad" at all (except maybe for testing)
If you haven't already, take a look at the chapters in Soares on grounding electrodes and testing them.
- Location
- Illinois
- Occupation
- retired electrician
Other than for some minimal protection from lightning and/or contact with a higher voltage system, the connection to earth does almost nothing to improve the safety of a facility electrical system operating at 1000 volts or less.
Even where used for grounding of instrumentation and computer systems, maintaining a single point of correction between earth and the system neutral is far more important than the quality of the connection to earth.
I see you got that from here.
At least your on the site..
At least your on the site..
Triad grounding
good day. i am trying to understand the principle or theory behind triad grounding. i am search the net but nothing as yet. any one with information or have used triad grounding could you please shed some light.
forums.mikeholt.com
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Does anyone actually test ground resistance on a regular basis in the US? Since it just does not matter much, why waste time and money testing it?
And what would the pass/fail point be? 100 Ohms? 1 Ohm?
And what would the pass/fail point be? 100 Ohms? 1 Ohm?
We had it tested here a few years back.. we were losing analog input modules like crazy during lightning strikes and the grounding efficacy came into question. Found a few rods that were in the 30s of Ohms but that was likely never the issue anyway. Isn't the pass point pretty clearly 25 Ohms based on the NEC though, regardless if you think that value is actually any sort of meaningful threshold?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
The code does not actually require that. It is 25 ohms if you have a single rod. If you have two rods or a cee, there is no ohms requirement at all.
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