Triangle Ground Electrode System

[jrturner]

NEC 250.56 states that a single electrode that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode. (Two electrodes is the maximum required.)

Why do so many consultants specify three rods spaced 10' apart when two electrodes are all that is required per NEC?

 

[luke warmwater]

Re: Triangle Ground Electrode System

2 reasons:
1) The NEC is a minimum standard
2) Most of them are probably either mis-informed or improperly trained in the way grounding should be done

 

[charlie b]

Re: Triangle Ground Electrode System

Todd: I agree with your first reason, but think that the wording of your second is a bit harsh. jrturner: I cannot independently confirm your statement that ?so many consultants? specify that configuration. But I will offer that the type of facility, the size of the facility, the complexity of the facility?s power distribution system, and the types of loads might warrant installation of more than 2 rods.

 

[bob]

Re: Triangle Ground Electrode System

I think that most consultants do not specity the minimum. You know that one rod will seldom do the job. The rods should be spaced at least twice the length of the rod. If the rod is 10 ft. long the rods should be 20 ft apart.

 

[dereckbc]

Re: Triangle Ground Electrode System

Luke Warmwater, the configuration is referred to as a "TRIAD". The NEC is only a minimum and therefore can be exceeded.

I agree with Charlie that site conditions dictate the specifications. I commonly use ground rings with 10' rods or chemical rods attached every 20' along the perimeter of the ring.

So why do they specify 3 rods?. Because they pay for it to cover there A$$.

 

[brian john]

Re: Triangle Ground Electrode System

I've stated this before and state one more time (probably not the last). If a engineer, end user ect has a standard maximum acceptable resistance for a grounding electrode system why don't they request a 4 point test prior to installation of the grounding electrode to determine what design they should utilize. A triad system may not be adequate.

A lot of issues play into the design of grounding electrodes systems, and it is a bit harsh to make a blanket statement about consultants, engineers and electricians. Why do electricians utilize EMT in some installations when type NM might be adequate? Safety, CYAing, experience ect.........

 

[tom baker]

Re: Triangle Ground Electrode System

Brian. Right 100% on your comment. I often see specs with a 5 ohm resistance, and they want the contractor to keeping adding ground electrodes until 5 ohms is met. the correct way would be to do a 4 point earth resistance test, design the grounding system to match the soil resistivity.

 

[dereckbc]

Re: Triangle Ground Electrode System

Brian and Tom the answer is simple. The engineer is delegating the contrator to do that. If you get a spec that requires a specified resistance, and you bid and win, guess what?

 

[luke warmwater]

Re: Triangle Ground Electrode System

Charlie B: I was in a harsh kind of mood at the time. (but notice, I did say most(not all) and probably (not definately)).

Dereck: I know what the configuration is. NEC is minimum, that's what I stated before.

Brian John: My intention was not to make a 'blanket statement' about ALL consultants, engineers, and electricians, but rather about the consultants that jrturner is refering to as per the reasoning in charlie b's post. Who are all of these 'consultants'?

jrturner: if there are 'so many consultants' who specify this arrangement, then I'll stick to my first post as per bob's reasoning: (10 feet apart is not utilizing the full potential of the ground rod(s)).

 

[karl riley]

Re: Triangle Ground Electrode System

Any electrician obeying grounding specs is operating within an ocean of ignorance and unstated assumptions. (How's that for an opening statement?)

So, swimming in this ocean one: meets NEC; two: installs according to required specs; three: avoids asking embarassing questions, such as "What is the reason for these specs".

I never was able to make it to three.

Karl

 

[brian john]

Re: Triangle Ground Electrode System

jrturner: if there are 'so many consultants' who specify this arrangement, then I'll stick to my first post as per bob's reasoning: (10 feet apart is not utilizing the full potential of the ground rod(s)).

But the NEC only makes you space them at a minimum 6 ft apart? Wonder where this came from.
Small town house projects?