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 Post subject: Short Circuit Current Labels
PostPosted: Sun Jun 18, 2017 11:19 am 
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Just wondering what people's experiences have been regarding the NEC's increasing requirements for short circuit current / ratings to be on labels? I know there are exceptions but has any one labeled equipment with the calculated short circuit current?


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 Post subject: Re: Short Circuit Current Labels
PostPosted: Sun Jun 18, 2017 7:27 pm 
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It has been a requirement for industrial control panels for I think at least 10 years.

In reality unless the panel shop is UL 809A, I RARELY see it actually done in practice. In the end though the easiest way to meet the requirement is to build the panel with a circuit breaker set up as the disconnect for the entire panel and then simply put the same information on the label that is on the breaker. It is slightly more complicated than that but not much. If you don't use a breaker or fuses as the main disconnect then you have a lot more work to do because it becomes a matter of determining which component is the weakest in terms of short circuit rating.


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 Post subject: Re: Short Circuit Current Labels
PostPosted: Mon Jun 19, 2017 6:42 am 
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Yes, there is an increasing list of requirements for the available short circuit current calculations/labeling and specific equipment.

110.9 has required that equipment have an adequate interrupting or withstand rating for as long as I can remember but new language is working its way into other areas. I reference a few of these areas here.

110.16 has been evolving and the latest iteration has very specific requirements for not only the available short circuit current but also the clearing time of the upstream device based on the short circuit current.

This information can be helpful with the NFPA 70E PPE Category Tables to verify the listed maximum fault current and clearing time. However, the exception states you do not need this information if you have an arc flash label (Implies NFPA 70E label requirements are met but it does not specifically require this)

110.24 requires the calculated fault current to be listed on service equipment but also provides an exception for industrial installations where conditions of maintenance and supervision ensure that only qualified persons service the equipment.

430.99 requires the available short circuit current be documented for motor control centers but it does not say how this is done. I imagine a traditional short circuit study might be suitable.

Here are the specific sections:

110.16 (B) Service Equipment.
In other than dwelling units, in addition to the requirements in (A), a permanent label shall be field or factory applied to service equipment rated 1200 amps or more. The label shall meet the requirements of 110.21(B) and contain the following information:
(1) Nominal system voltage
(2) Available fault current at the service overcurrent protective devices
(3) The clearing time of service overcurrent protective devices based on the available fault current at the service equipment
(4) The date the label was applied

Exception: Service equipment labeling shall not be required if an arc flash label is applied in accordance with acceptable industry practice.

Informational Note No. 1: NFPA 70E -2015, Standard for Electrical Safety in the Workplace, provides guidance, such as determining severity of potential exposure, planning safe work practices, arc flash labeling, and selecting personal protective equipment.

Informational Note No. 2: ANSI Z535.4-2011, Product Safety Signs and Labels, provides guidelines for the design of safety signs and labels for application to products.

Informational Note No. 3: Acceptable industry practices for equipment labeling are described in NFPA 70E -2015 Standard for Electrical Safety in the Workplace. This standard provides specific criteria for developing arc-flash labels for equipment that provides nominal system voltage, incident energy levels, arc-flash boundaries, minimum required levels of personal protective equipment and so forth.

110.24 Available Fault Current.
(A) Field Marking. Service equipment at other than dwelling units shall be legibly marked in the field with the maximum available fault current. The field marking(s) shall include the date the fault-current calculation was performed and be of sufficient durability to withstand the environment involved. The calculation shall be documented and made available to those authorized to design, install, inspect, maintain, or operate the system.

Informational Note: The available fault-current marking(s) addressed in 110.24 is related to required short-circuit current ratings of equipment. NFPA 70E -2015, Standard for Electrical Safety in the Workplace, provides assistance in determining the severity of potential exposure, planning safe work practices, and selecting personal protective equipment.

(B) Address revising the calculation if changes are made.

Exception: The field marking requirements in 110.24(A) and 110.24(B) shall not be required in industrial installations where conditions of maintenance and supervision ensure that only qualified
persons service the equipment.

430.99 Available Fault Current.
The available short circuit current at the motor control center and the date the short circuit current calculation was performed shall be documented and made available to those authorized to inspect the installation.


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 Post subject: Re: Short Circuit Current Labels
PostPosted: Mon Jun 19, 2017 7:20 am 
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It seems like the code people keep adding new code requirements yet, as Paul pointed out, they are rarely followed. I personally would like to see more core requirements, provided they make sense, to keep electrical systems safe. Unless the there is a mechanism to enforce these requirements it does little good to have these requirements unless a permit is pulled. The real issue is not the safety of knowing the short circuit level or the rating it is having a qualified understanding of what it means. Most people don't know, don't care, and mostly don't want to pay for it.

But to answer your question - I only see it if there is an arc flash study done.


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 Post subject: Re: Short Circuit Current Labels
PostPosted: Mon Jun 19, 2017 7:37 am 
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engrick wrote:
It seems like the code people keep adding new code requirements yet, as Paul pointed out, they are rarely followed. I personally would like to see more core requirements, provided they make sense, to keep electrical systems safe. Unless the there is a mechanism to enforce these requirements it does little good to have these requirements unless a permit is pulled. The real issue is not the safety of knowing the short circuit level or the rating it is having a qualified understanding of what it means. Most people don't know, don't care, and mostly don't want to pay for it.

But to answer your question - I only see it if there is an arc flash study done.


Agreed! 110.16 and 110.24 seem tied to electrical safety/arc flash studies but I question 430.99. It seems this is already covered by 110.9 which requires adequate interrupting ratings making this requirement redundant.

Back in the late 1970's at my co-op job in plant engineering, no one knew what any of this was. I asked when looking at a catalog for breakers. The philosophy seemed to be "If it fits, it works, if it fails, replace it" Many still seem to stick to this (incorrect) philosophy.


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 Post subject: Re: Short Circuit Current Labels
PostPosted: Mon Jun 19, 2017 7:46 am 
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There was also a change to 670.5 in the 2017 NEC that requires the available short circuit current be labeled on industrial machinery, in addition to the short circuit rating of the machinery. We've solved this by printing the available kA on the arc flash label (careful not to use arcing current; use bolted kA). Our arc flash labels already have the date on there so we satisfy that requirement as well. We liked combining the arc flash with short circuit so that you don't end up with label overload on equipment.


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 Post subject: Re: Short Circuit Current Labels
PostPosted: Mon Jun 19, 2017 8:33 am 
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We have a template and can currently print labels that list the Short Circuit Current at each bus (piece of equipment). Since the SC labeling NEC requirements have increased, we are planning on modifying our Arc Flash Label template to always list the Maximum Short Circuit Current at each bus. This will "kill two birds with one stone"

_________________
Robert Fuhr, P.E.; P.Eng.
PowerStudies


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 Post subject: Re: Short Circuit Current Labels
PostPosted: Mon Jun 19, 2017 10:15 am 
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Few years ago, even for new equipment, you design switchgear, switchboard, motor control centers, panelboards, pedestals and ship it to the customer. The customer or their consultant engineers almost take forever to approve arc flash/short circuit study and by the time it gets approved and labels are printed, the equipment would be commissioned and running for several months in the field. But slowly that is changing, mainly because people are more aware of electrical hazards, and so as inspectors. Thanks to many experts and gururs here for educating people working in electrical industry. Now many specification for new equipment comes with some kind of following language:
"An initial, complete Short Circuit and Arc Flash Studies shall be submitted and reviewed by Engineer before Engineer will approve submittal for
MCC or Switchboard equipment.The protective device coordination study shall be submitted and approved prior to start of field breaker tests." With this, the studies has to be done and changes and mitigation (if required) has to be submitted first. Then this changes has to be reflected in the electrical design and submit for approval. Then only the equipment can be released to production after approval and the arc flash/short circuit labels would be affixed prior to shipping. I was curious because we saw NEC Article 110.16 & 110.24 requirements since 2011 edition and why now. But no wonder! I heard that now many inspectors insist they gave enough years to incorporate NEC changes and doesn't allow to commission unless he/she see the arc flash/short circuit labels on the equipment and that the workers working on energized equipment has PPE per study. The change may be hard, but it is a good change. After all, Arc flash is a low frequency high consequence event and it should not be under estimated.


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