NEC Article 240.87 2014 Revision

[edtjlt]

Unlike previous editions the revised language doesn't seem to state that this article applies only when a circuit breaker is used which has no instantaneous setting. Therefore it appears to require the use of one of the listed reduced clearing time (hence reduced energy) methods. Comments?

 

[luckylerado]

Here is the commentary on this from this section out of the 2014 handbook.

"Where a circuit-breaker trip unit does not provide the capability
for an instantaneous response to a short circuit, 240.87 requires
that (1) the location of the device in the electrical system be documented,
and (2) a means be provided in the system to limit the
energy that personnel may be exposed to while working on energized
equipment.
Circuit breakers without the capability of an instantaneous
response can be used to selectively coordinate with other OCPDs
where required by the Code or where incorporated as part of an
electrical system design. However, a longer protective device
opening time can expose the person(s) who may have initiated
the fault while working on energized electrical equipment to more
incident energy, thus increasing the severity of the hazard. This
section identifies four specific methods that can be used to comply
with this requirement and also permits use of an equivalent, which
is acceptable to the AHJ. Zone-selective interlocking and differential
relaying are methods that can be implemented as part of the
system design and do not require any manual intervention.
An energy-reducing maintenance switch is a means by which
an intentional delay in the opening of a circuit breaker can be
overridden while maintenance, service, or diagnostic tasks are
being performed. The circuit breaker can then be restored upon
completion of the tasks to enable the system to be selectively
coordinated or for other system design purposes.
The Code does not prohibit the use of these methods to limit
fault current in systems where circuit breakers having an instantaneous
capability are installed and adjusted to allow for a longer
clearing time. This is a design consideration and is not required
by this section."

 

[mwm1752]

The CMP had several comment on the lack of direction for instantaneous trip breakers since it does not directly mention them.

The question I would submit is if 240.87(B)(3) refers to an intentional adjustment to delay the breaker from opening which can be reset back to the standard delay time to which the breaker was intended to use --

Would a instantaneous trip breaker having a standard delay time equal or short than an electronic trip unit breaker that employs an energy reducing maintence switch fit the method of an approved equivelant means as per 240.87(B)(5)?

Here are comments from a Seimens white paper;
In the 2011 NEC, only applications where an instantaneous device was not present were required to provide additional means to reduce arc-fault energy. In 2014, the wording was changed such that a properly adjusted instantaneous device was not included in the list of approved energy-reducing measures. A properly adjusted instantaneous trip setting - meaning one that is set above the nuisance trip level but below the anticipated arc-fault level - is actually often a more effective means to reduce arc energy than the other four listed measures. Normally, the fastest possible clearing time of a circuit breaker occurs when it operates in its instantaneous region. Siemens circuit breakers have no intentional delay in the instantaneous trip settings. In molded case circuit breakers, this properly-set instantaneous operation will usually clear a fault somewhere between one third of a cycle and one cycle (approximately 6 to 17ms).

 

[don_resqcapt19]

In the draft copy of this section the section title was still "Noninstantaneous Trip.".
This was changed at the ROC stage.
blue = new text red = text to be deleted

(240.87)
________________________________________________________________
Submitter: Christopher G. Walker, Eaton Corporation
Comment on Proposal No: 10-53a
Recommendation: Revise text to read as follows:
240.87 Noninstantaneous Trip Arc Energy Reduction. Where a circuit breaker:
(1) Utilizes short time delay Rated 1,000Amps and above and
(2) Does not have an adjustable instantaneous trip function engaged and
(3) Does not have an instantaneous override or the instantaneous override
setting is above the arcing current then (A) and (B) shall apply.
(A) Documentation. Documentation shall be available to those authorized to design, install, operate, or inspect the installation as to the location of the circuit breaker(s).
(B) Method to Reduce Clearing Time. One of the following means shall be provided:
(1) Zone-selective interlocking or
(2) Differential relaying or
(3) Energy-reducing maintenance switching with local status indicator or
(4) Energy-reducing active arc flash mitigation system
(5) An approved equivalent means

Informational Note No. 1: An energy-reducing maintenance switch allows a worker to set a circuit breaker trip unit to ?no intentional delay? to reduce the clearing time while the worker is working within an arc-flash boundary as defined in NFPA 70E-2009, Standard for Electrical Safety in the Workplace, and then to set the trip unit back to a normal setting after the potentially hazardous work is complete.

Informational Note No. 2: An energy-reducing active arc flash mitigation system helps in reducing arcing duration in the electrical distribution system. No change in circuit breaker or the settings of other devices is required during maintenance when a worker is working within an arc-flash boundary as defined in NFPA 70E-2012, Standard for Electrical Safety in the Workplace.

Substantiation: The first change is to correct the title to ?Arc Energy Reduction? as that is the intent of this section. This aligns with the NEMA affirmative comment by Mr. A. Manche.

The language accepted at the ROP meetings could extend the interpretation of this requirement to apply to many smaller molded case circuit breakers which were not originally intended to be addressed, (down to a 225A frame based upon products available from at least one manufacturer).

The ROP accepted language also makes it extremely difficult for the AHJ to enforce as they must now determine arcing currents for each circuit breaker being inspected.

In the panel statement to the rejection of Proposal 10-54, it is understood that the 1000A level is not the sole criteria for increasing arc flash hazards, but recognizes that not having an instantaneous trip affects it too. This comment proposes that BOTH 1000A AND the instantaneous trip engagement be used as the determining factor. This removes the requirement from the smaller molded case breakers which were not originally intended to be addressed. It also makes the applicability of this requirement clear and enforceable by the AHJ.

Panel Meeting Action: Accept in Principle in Part

Revise comment to read as follows:
240.87 Arc Energy Reduction. Where the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted is 1200 amperes or higher then (A) and (B) shall apply.
(A) Documentation. Documentation shall be available to those authorized to design, install, operate, or inspect the installation as to the location of the circuit breaker(s).
(B) Method to Reduce Clearing Time. One of the following or approved equivalent means shall be provided:
(1) Zone-selective interlocking or
(2) Differential relaying or
(3) Energy-reducing maintenance switching with local status indicator or
(4) Energy-reducing active arc flash mitigation system or
(5) An approved equivalent means

Informational Note No. 1: (no change)

Informational Note No. 2: An energy-reducing active arc flash mitigation system helps in reducing arcing duration in the electrical distribution system. No change in circuit breaker or the settings of other devices is required during maintenance when a worker is working within an arc-flash boundary as defined in NFPA 70E-2012, Standard for Electrical Safety in the Workplace.
Panel Statement: CMP-10 accepts the title change to better reflect the subject.
The panel rejected the proposed revisions to items (2) and (3) because the panel has deleted those list items to provide clarity for this requirement. The panel increased 1000 to 1200 amperes to limit the number of circuit breakers affected.

Number Eligible to Vote: 12
Ballot Results: Affirmative: 9 Negative: 3

Explanation of Negative:
DARLING, D.: The following is a quote from the ROP on Proposal 10-54:
?Panel Statement: Arc-flash hazards are not increased simply because the ampere rating of a circuit breaker equals or exceeds 1000 amperes. Arc-flash hazards however may be increased when the circuit breaker does not have an instantaneous trip capability.? The Panel action on this Comment contradicted the earlier panel statement. The Panel offered no technical substantiation for including these requirements for all breakers 1200A and above and did not explain in the panel statement the ramifications of deleting lines two and three. The comment as revised by the Panel expanded the requirement to include breakers with instantaneous trip which the original proposal continued to exclude. The panel discussion indicates that instantaneous trip is a useful criteria for limiting arc flash hazard but this should be made clear in the code language itself. The comment should be revised to continue to exclude breakers with instantaneous trip. A risk analysis needs to be performed to determine
what is necessary for effective mitigation of injury to personnel from the hazards of arc flash.

FREDERICKS, C.: I disagree with the panel action; the panel should have accepted the title change only. There was no substantiation provided that
breakers rated at and above either 1000 or 1200 amperes have increased arc flash hazards just based on their size, as the panel correctly stated at the ROP stage. The comment and the accepted code text do not even contain an arc flash energy level target, so will result in an unnecessary requirement for some installations and could give an unwarranted belief about safety for others. Also I believe the panel action in deleting item (2) from the existing 240.87 text is a significant error, because the code text no longer acknowledges that that a breaker instantaneous function could meet the intent of the 240.87 requirement. If the breaker has an instantaneous function engaged that is responsive to the minimum arcing current, then no energy reduction below that is possible, even with an additional maintenance switch or any other additional provision.

The change in deleting item (2) from the existing 240.87 text was not requested by the submitter and was not substantiated in the panel statement, so I believe that is a further reason this part of the panel action is in error. If this part of the panel action remains in place after the written ballot, I believe it should be reviewed by the Correlating Committee. An additional editorial problem in the accepted text is that (B)(5) is redundant to text in (B); I believe this should be corrected editorially regardless. Please see also my explanations of negative vote provided for Comments 10-21 and 10-28.

VARTANIAN, J.: At the review of the comments for this proposal, the changes made removed a key part of 240.87. Removal of the instantaneous trip function removes a significant part the limitation of an arc-flash hazard, using the circuit breaker rating of 1200 amps does not take the place of limiting the arc-flash hazard. Additional clarity is needed in the text to address limiting the arc-flash hazard. Comment 10-24 along with proposal 10-53a must be rejected and the language returned to the 2011 language until acceptable language can be developed and supported by the industry.

Comment on Affirmative:
KAUER, R.: Code Panel 10 did not make it clear that the instantaneous breaker should be accepted as a means to mitigate arc flash energy. If the
instantaneous function is permitted as an alternative means to mitigate the arc energy, than it should have been added to the list of solutions.
Because it is not spelled out in the code language, the authority having jurisdiction in one part of the country may accept the instantaneous function as an alternative method and an inspector in another part may not. I don?t believe that the way it is written now, that we have good code language that is enforceable. I know that it does not say that instantaneous function cannot be used but it does not say that it can.