Understanding the NEC 2008 Book Questions

[tencatia]

We are using Mike's book in our class and have had differences on some of the supplied answers. The following qustion has brought on a lively discussion.

Q: Ground fault protection of equipment is required for the feeder disconnect if.
a. it is a solidly-grounded wye system
b. it is more than 150 volts-to-ground, but not exceeding 600v phase-to-phase
c. the feeder is rated 1,000 or less
d. all of these
e. a & b / We all agree that the answer is e./ We disagree on the code reference.
The answer key says it is 215.10
Several of us believe it could also be 230.95
So we thought we'd ask the experts...

 

[roger]

Look at the question closely, it is dealing with feeders, not services.

Roger

 

[jim dungar]

I disagree with your answer of "e".
What differences do you notice between 215.10 and 230.95?

 

[cschmid]

here are the codes from the hand book see if this helps you out...

215.10 Ground-Fault Protection of Equipment.
Each feeder disconnect rated 1000 amperes or more and installed on solidly grounded wye electrical systems of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase, shall be provided with ground-fault protection of equipment in accordance with the provisions of 230.95.
FPN: For buildings that contain health care occupancies, see the requirements of 517.17.
Exception No. 1: The provisions of this section shall not apply to a disconnecting means for a continuous industrial process where a nonorderly shutdown will introduce additional or increased hazards.
The intent of 215.10 is to require ground-fault protection of equipment for feeder disconnects that are rated 1000 amperes or more at 480Y/277 volts. A similar requirement for services is found in 230.95. The reason for the requirement is the unusually high number of burndowns reported on feeders and services in this voltage range. Prior to being put into service, each ground-fault protection system must be performance tested and documented according to the requirements of 230.95(C).
It should be noted that ground-fault protection of feeder equipment is not required if protection is provided on an upstream feeder or at the service. However, additional levels of ground-fault protection on feeders may be desired so that a single ground fault does not de-energize the whole electrical system. See 230.95 for further commentary on ground-fault protection of services. Also, see 517.17, which requires an additional level of ground-fault protection for health care facilities.
For emergency feeders, according to Article 700, the ground-fault protection requirements are different. See 700.26 for further details.
Exception No. 2: The provisions of this section shall not apply if ground-fault protection of equipment is provided on the supply side of the feeder and on the load side of any transformer supplying the feeder.
Ground-fault protection installed in equipment supplying a transformer will not function to protect equipment supplied by the secondary of the transformer. If the equipment supplied by the secondary of the transformer meets the parameters under which GFPE is required by 215.10, protection must be installed within that equipment notwithstanding any GFPE installed in equipment supplying the transformer.


230.95 Ground-Fault Protection of Equipment.
Ground-fault protection of equipment shall be provided for solidly grounded wye electric services of more than 150 volts to ground but not exceeding 600 volts phase-to-phase for each service disconnect rated 1000 amperes or more. The grounded conductor for the solidly grounded wye system shall be connected directly to ground through a grounding electrode system, as specified in 250.50, without inserting any resistor or impedance device.
The rating of the service disconnect shall be considered to be the rating of the largest fuse that can be installed or the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted.
See the definition of ground-fault protection of equipment in Article 100. Ground-fault protection of equipment on services rated 1000 amperes or more operating at 480Y/277 volts was first required in the 1971 Code because of the unusually high number of burndowns reported on those types of service. This requirement does not apply to systems where the grounded conductor is not solidly grounded, as is the case with high-impedance grounded neutral systems covered in 250.36.
Ground-fault protection of services does not protect the conductors on the supply side of the service disconnecting means, but it is designed to provide protection from line-to-ground faults that occur on the load side of the service disconnecting means. An alternative to installing ground-fault protection may be to provide multiple disconnects rated less than 1000 amperes. For instance, up to six 800-ampere disconnecting means may be used, and in that case ground-fault protection would not be required. FPN No. 2 to 230.95(C) recognizes that ground-fault protection may be desirable at lesser amperages on solidly grounded systems for voltages exceeding 150 volts to ground but not exceeding 600 volts phase to phase.
In addition to providing ground-fault protection, engineering studies are recommended to determine the circuit impedance and short-circuit currents that would be available at the supply terminals, so that equipment and overcurrent protection of the proper interrupting rating are used. See 110.9 and 110.10 for details on interrupting rating and circuit impedance.
The two basic types of ground-fault equipment protectors are illustrated in Exhibits 230.28 and 230.29. In Exhibit 230.28, the ground-fault sensor is installed around all the circuit conductors, and a stray current on a line-to-ground fault sets up an unbalance of the currents flowing in individual conductors installed through the ground-fault sensor. When this current exceeds the setting of the ground-fault sensor, the shunt trip operates and opens the circuit breakers.

Exhibit 230.28 A ground-fault sensor encircling all circuit conductors, including the neutral.

Exhibit 230.29 A ground-fault sensor encircling only the bonding jumper conductor.
The ground-fault sensor illustrated in Exhibit 230.29 is installed around the bonding jumper only. When an unbalanced current from a line-to-ground fault occurs, the current flows through the bonding jumper and the shunt trip causes the circuit breaker to operate, removing the load from the line. See also 250.24(A)(4), which permits a grounding electrode conductor connection to the equipment grounding terminal bar or bus.
Exception: The ground-fault protection provisions of this section shall not apply to a service disconnect for a continuous industrial process where a nonorderly shutdown will introduce additional or increased hazards.
Most fire pumps rated 100 hp and over would require a disconnecting means rated at 1000 amperes or more. However, due to the emergency nature of their use, fire pumps are exempt from the provisions of 230.95.
(A) Setting. The ground-fault protection system shall operate to cause the service disconnect to open all ungrounded conductors of the faulted circuit. The maximum setting of the ground-fault protection shall be 1200 amperes, and the maximum time delay shall be one second for ground-fault currents equal to or greater than 3000 amperes.
The maximum setting for ground-fault sensors is 1200 amperes. There is no minimum setting, but it should be noted that settings at low levels increase the likelihood of unwanted shutdowns. The requirements of 230.95 place a restriction on fault currents greater than 3000 amperes and limit the duration of the fault to not more than 1 second. This restriction minimizes the amount of damage done by an arcing fault, which is directly proportional to the time the arcing fault is allowed to burn.
Care should be taken to ensure that interconnecting multiple supply systems does not negate proper sensing by the ground-fault protection equipment. A careful engineering study must be made to ensure that fault currents do not take parallel paths to the supply system, thereby bypassing the ground-fault detection device. See 215.10, 240.13, 517.17, and 705.32 for further information on ground-fault protection of equipment.
(B) Fuses. If a switch and fuse combination is used, the fuses employed shall be capable of interrupting any current higher than the interrupting capacity of the switch during a time that the ground-fault protective system will not cause the switch to open.
(C) Performance Testing. The ground-fault protection system shall be performance tested when first installed on site. The test shall be conducted in accordance with instructions that shall be provided with the equipment. A written record of this test shall be made and shall be available to the authority having jurisdiction.
The requirement for ground-fault protection system performance testing is a result of numerous reports of ground-fault protection systems that were improperly wired and could not or did not perform the function for which they were intended. This Code and qualified testing laboratories require a set of performance testing instructions to be supplied with the equipment. Evaluation and listing of the instructions fall under the jurisdiction of those best qualified to make such judgments, the qualified electrical testing laboratory (see 90.7). If listed equipment is not installed in accordance with the instructions provided, the installation does not comply with 110.3(B).
FPN No. 1: Ground-fault protection that functions to open the service disconnect affords no protection from faults on the line side of the protective element. It serves only to limit damage to conductors and equipment on the load side in the event of an arcing ground fault on the load side of the protective element.
FPN No. 2: This added protective equipment at the service equipment may make it necessary to review the overall wiring system for proper selective overcurrent protection coordination. Additional installations of ground-fault protective equipment may be needed on feeders and branch circuits where maximum continuity of electric service is necessary.
FPN No. 3: Where ground-fault protection is provided for the service disconnect and interconnection is made with another supply system by a transfer device, means or devices may be needed to ensure proper ground-fault sensing by the ground-fault protection equipment.
FPN No. 4: See 517.17(A) for information on where an additional step of ground-fault protection is required for hospitals and other buildings with critical areas or life support equipment.

 

[tencatia]

Understanding the NEC 2008 Book Questions

I disagree with your answer of "e".
What differences do you notice between 215.10 and 230.95?

The answer of "e." was supplied with the answer key that accompanied the textbook.

 

[jim dungar]

The answer of "e." was supplied with the answer key that accompanied the textbook.

OOPs, I didn't read <1000A correctly.

 

[bob]

I must be missing something but I believe the answer is none of the above.
The code references both require that the equipment be rated 1000 amps or more and that option is not listed. If you have a and b and the equipment is rated 400 amps do you need GFI protection?

 

[tencatia]

I must be missing something but I believe the answer is none of the above.
The code references both require that the equipment be rated 1000 amps or more and that option is not listed. If you have a and b and the equipment is rated 400 amps do you need GFI protection?

The question asks us to select when it is required. c. states: " the feeder is rated 1,000 or less" so it would not be required.

 

[bob]

The question asks us to select when it is required. c. states: " the feeder is rated 1,000 or less" so it would not be required.

Its not required for a and its not required for b. It is require when you have a and b and the service is rated 1000 amps or greater.

 

[tencatia]

Its not required for a and its not required for b. It is require when you have a and b and the service is rated 1000 amps or greater.

You are correct sir! That is why the answer is e. and not c or d. The original post states where we got the question and answer and that we were looking for some guidance. Our class must be right on track because we are having discussions similar to the replys I am finding here.
Thank you all for your input.

 

[don_resqcapt19]

You are correct sir! That is why the answer is e. and not c or d. The original post states where we got the question and answer and that we were looking for some guidance. Our class must be right on track because we are having discussions similar to the replys I am finding here.
Thank you all for your input.

It is a poorly worded question. There is no correct answer as it is written becuase there is no requirement to provide GFP unless you have the conditions in "a" and "b" and the feeder OCPD is rated at 1000 amps or more. The anwer "e" only contains two of the three conditions that are required to trigger the GFP requirement. Without the third part there is no requirement to provide GFP and no correct answer as the question is shown in you original post.

 

[bob]

The answer is not "e". The answer is none of the above as Don has stated.

 

[inspector141]

[I]Test taker:[/I] Answer is e. you have no choice

Test maker:[/U] answer is e unless you reword it. It would be confusing to the test taker if you put none of the above with the same question along with same answers for a,b&c. I am not suggesting that some of you would word the question that way, but it would be confusing.

It is not a terrible question because the test taker can only answer e. It is clearly the best answer. In other words, the test taker would/should know that it must be a 1000 amps or more even without that being one of the answers. It is rather clever that they inserted 1000 amps or less and then offerd d as all of the above, imo.
What if you left out solidly grounded wye electric, but inserted 1000 amps or more in its place and kept the 150 volts or more but not exceeding 600 volts phase to phase as answers?
Well then, according to your logic, you would have to pick none of the above because you left out the solidly grounded requirement. Again, confusing.
It doesn't make it a bad question because you left out one of the three requirements.
Unfortuntely, if you put all three correct answers for a,b&c, and d as (all of the above), it is too easy of an answer. Why? Because the test taker might know that one or two of the answers are correct, then he must choose all of the above. But if you have two that are correct and one that is incorrect, the test taker can't guess quite as easily.

Typically multiple choice tests have 4 answers, not 5.

 

[bob]

Marty
My point is that the question states

Q: Ground fault protection of equipment is required for the feeder disconnect if.
a. it is a solidly-grounded wye system
b. it is more than 150 volts-to-ground, but not exceeding 600v phase-to-phase
c. the feeder is rated 1,000 or less
d. all of these
e. a & b

None of the answers require a GFI by the code. a and b do not require a GFI. This is a very poor quesrtion.

 

[don_resqcapt19]

Marty,
I disagree....this is a terrible question and there is no correct answer as written. If you don't have all 3 of the conditions, there is no requirement for GFP. To say "e" is a correct answer is saying that GFP is required even where the OCPD is less than 1000 amps and that is wrong.

 

[A/A Fuel GTX]

I think the test writer assumed the situation was over 1K amps and figured the taker would also. I came up with the A & B answer having not over analyized the question. A & B are the only two choices that could apply as C would definately not.....

 

[A/A Fuel GTX]

I was always taught that when taking a test, choose the BEST answer..

 

[don_resqcapt19]

I was always taught that when taking a test, choose the BEST answer..

That is the only thing that you can do when you are taking the test and have an invalid question like this one, but that still does not make the question valid.

 

[inspector141]

I agree that it is not a good question. But a test question is not a code discussion where all points can be debated and settled. My main point is that the question and answers are not confusing even though there is one additional requirement for GFP. If the test taker knows the subject, he/she would clearly answer with e.

 

[don_resqcapt19]

. If the test taker knows the subject, he/she would clearly answer with e.

If the test taker knows the code, he can't possibly choose "e" as the correct answer becuase the two conditions covered by the answer "e" do not trigger the requirement for GFP.
Well, I guess in the test he or she would have to take "e" as the answer, but this is a case where I would be writting a stongly worded comment on the answer sheet telling them that they do no have a valid question and that it should be removed from the scoring as there is no correct answer given.