Question Section 250.56

[gary b]

A question came up in class I cannot answer. Will you explain why metal frame of a building and concrete encased electrodes, both suitable as ?stand alone? electrodes, are no longer allowed as augmented electrodes in 250.56 but are allowed for a supplemental electrode for metal water pipes in 250.53(C)(2)?

 

[Cavie]

CEE is a stand alone electrode and required to be used.

 

[gary b]

Yes, that is understood, if a CCE is installed and the installer, for some reason installs one ground rod that is not tested to 25 ohms, the CCE is not allowed to be used as the augmented electrode required in 250.56. Why?

 

[infinity]

Yes, that is understood, if a CCE is installed and the installer, for some reason installs one ground rod that is not tested to 25 ohms, the CCE is not allowed to be used as the augmented electrode required in 250.56. Why?

Why not? 250.56 says that one of the electrodes in 250.52(A)(2)-
(7) is permitted to augment the rod that has a resistance above 25 ohms. #3 on the list is the CEE.

 

[gary b]

I should have clarified this is in the 2008 NEC. 250.56 eliminates the use of metal and CCE.

 

[don_resqcapt19]

5-100 Log #1122 NEC-P05 Final Action: Accept in Principle
(250.56)
____________________________________________________________
Submitter: Andre R. Cartal, Princeton Borough Building Dept.
Comment on Proposal No: 5-174
Recommendation: Delete “shall be augmented by one additional electrode of any of the types specified by 250.52(A)(1) through 250.52(A)(7).”
Substantiation: The present wording of this section presents us with an endless loop of requirements. For example, 250.52(A)(2), (3), and (4) are
individually or collectively permitted without a supplemental electrode. Including them in 250.56 makes no sense as there is no resistance value and if they were installed 250.56 would NOT apply. I can see now why inspectors are requiring a concrete encased electrode to be AUGMENTED by ground rods.
Panel Meeting Action: Accept in Principle
Revise 250.56 to read as follows:
250.56 Resistance of Rod, Pipe, and Plate Electrodes
A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(4) through (A)(8). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.
FPN: The paralleling efficiency of rods longer than 2.5 m (8 ft) is improved by spacing greater than 1.8 m (6 ft).
Panel Statement: The requirement for a single electrode that does not have a resistance 25 ohms or less to be augmented does not apply to any electrodes other than rod, pipe, or plate. It is required to augment such an electrode with one additional electrode of any of the types specified by 250.52(A)(4) through 250.52(A)(8).
Number Eligible to Vote: 15
Ballot Results: Affirmative: 15
____________________________________________________________

 

[don_resqcapt19]

If you install a ground rod at a building where there is already a groundind electrode that of a type listed in 250.52(A)(2) through (A), then 250.56 does not apply as the ground rod would be an auxilliary (supplementary in 2005 code) grounding electrode. 250.54.
Don

 

[gary b]

If I understand you correctly you feel a ground rod installed with CCE would be considered by the Code as an auxiliary electrode and 250.54 would apply? How is this thought justified with 250.50 where all the electrodes present must be bonded together to form the grounding electrode system? I don?t think the ground rod would be considered an auxiliary because it is a grounding electrode.

I think the answer may be found in the ROP/ROC you sent. The panel states, ?The requirement for a single electrode that does not have a resistance 25 ohms or less to be augmented does not apply to any electrodes other than rod, pipe, or plate. It is required to augment such an electrode with one additional electrode of any of the types specified by 250.52(A)(4) through 250.52(A)(8).?

I would think from this statement the Panel intends for any made electrode installed (rod, pipe, or plate) must be augmented by types 250.52(A)(4)-(8). This would mean that if a CCE electrode and a ground rod was installed, the ground rod would need to be augmented by a type listed in 250.52(A)(4)-(8), thus CCE and two ground-rods installed.

Is this correct?

 

[don_resqcapt19]

Gary,
If the ground rod is not required to be installed by the code rules, then it becomes, in my opinion, an auxillary electrode.
I really don't know what the panel was tring to do here. There is no reason to have to drive 2 ground rods if you have building steel, CEE or a ground ring...there is also no reason to install even a single rod if you have one of these electrodes.
This one needs some work for 2011.
Don

 

[jshaw]

I think where you are getting confused is in the statement "all electrodes that are present". A ground rod is generally not "present" unless you put it there. If you have a CCE then a ground rod is not required, you don't install one, and it is therefore not "present" and is not required. If you choose to add a ground rod when it is not required then it becomes supplementary.

 

[gary b]

I can see your point if you install the rod at a parking lot pole light or some other equipment that is not directly or solidly connected to the GE or GEC. But I think if any of the listed electrodes are directly connected to the GE system with a 6 AWG or greater size it becomes a grounding electrode (250.50) not a auxiliary electrode in 250.54. Maybe my tunnel vision on this is incorrect. Please help me see the difference.

 

[gary b]

Don,
I agree with you about the ground rod. Why install it if you have CCE and the others that are natural part of the building process (metal water pipe, steel that is grounded, CCE) ? In 250.52(A)(2)(3) the metal frame of a building is allowed to be grounded by rods if 250.56 is followed.

I was told by another source that the intent of the panel was that all rods, pipes, plates installed must comply with 250.56 regardless of the other electrodes installed. I guess that means two or test if the rumor is true.

 

[don_resqcapt19]

Gary,
I really don't know the answer. I will stick with my opinion that if the rod is not required to be installed by the code, then 250.54 applies. If the rod is required to be installed then 250.56 applies.

I was told by another source that the intent of the panel was that all rods, pipes, plates installed must comply with 250.56 regardless of the other electrodes installed. I guess that means two or test if the rumor is true.

I don't see that in the wording of the new section. The rod can be supplemented by any of one of the electrodes in (A)(4) through (A)(7). There was no technical substantiation to remove the permission to use the building steel or the CEE for this purpose. The new wording and the panel statement make no sense to me.
Don

 

[crossman]

My thoughts:

2008 NEC 250.56 begins with "A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less..."

In my opinion, the key is "A single electrode". If we have a grounding electrode system consisting of a concrete encased electrode and a ground rod, then the ground rod is not "a single electrode" and therefore does not need to comply with 250.56 for 25 ohms or less to ground.

There are some different considerations if the electrode consisted of only a water pipe and rod, or in some instances, building steel and a rod as pointed out in 250.53(D)(2) and 250.52 A (2)(3).

 

[tryinghard]

A question came up in class I cannot answer. Will you explain why metal frame of a building and concrete encased electrodes, both suitable as ?stand alone? electrodes, are no longer allowed as augmented electrodes in 250.56 but are allowed for a supplemental electrode for metal water pipes in 250.53(C)(2)?

250-50 allows us to use a CCE (ufer) all by itself as well as all the other electrodes, but a water pipe electrode MUST BE supplemented regardless of ohms 250-53(D). This is due to the fact a non-skilled individual can alter it causing rendering it disabled. In my opinion the author intentionally convolutes the wording in 250-50.

The '05' Handbook gives a good explanation about 250-50, Grounding electrode system, 'the NEC encourages the formation of a system of electrodes" i.e. more than one. The Ufer is worthy of stand-alone but so are the others especially if they read low ohms, if in doubt install additional electrodes and form a system. I personally wouldn't bother because often I don't believe its necessary.

Grounding has a purpose and is important when used but bonding is far more critical and important. The likelihood of ever being used proves this; think about the purpose of grounding 250-(4)(A)(1):

? Lightning - could happen but the flash will travel multiple ways regardless of low ohms through electrodes to earth these may just get the majority of the voltage. If lightning is great concern install a designed lightning rod system.

? Line surges - could happen with upstream powerhouse problems or transformer failure but stuff is going to have to blow up or arc before an electrode will be used. A relay can be installed to shunt the main to circumvent this problem.

? Unintentional contact with higher-voltage lines - could happen and the downstream voltage will increase proportionally but again stuff is going to have to blow up or arc before an electrode will be used. And relays can be installed to shunt the main.

In premises wiring grounding to earth has nothing to do with how circuits function, bonding functions, ground fault functions, or neutrals function but bonding does!

Bonding is what enables 250-4(A)(4) & (5) effective ground fault current path. Without this fault path breakers will not trip and electrocution is highly likely. Because of the likelihood of use the bonding deserves more emphasis than grounding to earth.

 

[crossman]

In my opinion the author intentionally convolutes the wording in 250-50.

I completely agree with everything you wrote, except I do not understand the sentence above.

Still, even though bonding most likely saves many more lives than grounding (earthing?) ever has, that does not render the original posters question invalid.

 

[brother]

250-50 allows us to use a CCE (ufer) all by itself as well as all the other electrodes, but a water pipe electrode MUST BE supplemented regardless of ohms 250-53(D). This is due to the fact a non-skilled individual can alter it causing rendering it disabled. In my opinion the author intentionally convolutes the wording in 250-50.

The '05' Handbook gives a good explanation about 250-50, Grounding electrode system, 'the NEC encourages the formation of a system of electrodes" i.e. more than one. The Ufer is worthy of stand-alone but so are the others especially if they read low ohms, if in doubt install additional electrodes and form a system. I personally wouldn't bother because often I don't believe its necessary.

Grounding has a purpose and is important when used but bonding is far more critical and important. The likelihood of ever being used proves this; think about the purpose of grounding 250-(4)(A)(1):

? Lightning - could happen but the flash will travel multiple ways regardless of low ohms through electrodes to earth these may just get the majority of the voltage. If lightning is great concern install a designed lightning rod system.

? Line surges - could happen with upstream powerhouse problems or transformer failure but stuff is going to have to blow up or arc before an electrode will be used. A relay can be installed to shunt the main to circumvent this problem.

? Unintentional contact with higher-voltage lines - could happen and the downstream voltage will increase proportionally but again stuff is going to have to blow up or arc before an electrode will be used. And relays can be installed to shunt the main.

In premises wiring grounding to earth has nothing to do with how circuits function, bonding functions, ground fault functions, or neutrals function but bonding does!

Bonding is what enables 250-4(A)(4) & (5) effective ground fault current path. Without this fault path breakers will not trip and electrocution is highly likely. Because of the likelihood of use the bonding deserves more emphasis than grounding to earth.

Very interesting read. Here i thought the extra 2 rods at the panel was to help make sure that the breaker would trip and keep a neutral connection . sometimes the service neutral from the service utility gets lost so you need something to help keep the circuit going/clear a fault.

 

[JohnJ0906]

Very interesting read. Here i thought the extra 2 rods at the panel was to help make sure that the breaker would trip and keep a neutral connection . sometimes the service neutral from the service utility gets lost so you need something to help keep the circuit going/clear a fault.

In most cases there would be too much earth resistance for this to be an effective ground fault path. See 250.4(A)(5) last sentence.

 

[tryinghard]

I completely agree with everything you wrote, except I do not understand the sentence above.

that is:

by tryinghard, In my opinion the author intentionally convolutes the wording in 250-50.

The '05' handbook states this better; it says the NEC is intentionally unclear and places an emphasis on a system as opposed to a stand-alone electrode, in other words the wording can be fixed for a more direct meaning but the NEC hasn't incorporated this. When I read the handbook I found myself in agreement to its interpretation.

Still, even though bonding most likely saves many more lives than grounding (earthing?) ever has, that does not render the original posters question invalid.

I fully agree! I do hope that Gary will take this information to his class for discussion though. I find many Journeymen Electricians that do not understand the purpose and use of an electrode.

 

[crossman]

it says the NEC is intentionally unclear and places an emphasis on a system as opposed to a stand-alone electrode,

Gotcha. I didn't know whether the word "author" was referring to the Code Making Panels or to the original poster.