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 Post subject: Labeling Disconnects
PostPosted: Wed Jul 10, 2013 9:43 am 
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Joined: Mon Oct 10, 2011 4:07 pm
Posts: 11
Location: Phoenix
I see this topic has been discussed before in this forum but not since the NFPA 70E 2012 edition came out. Understanding the NEC 110.16 requirements of labeling equipment that is likely to require examination, adjustment, servicing etc..... in this groups opinion should a disconnect be labeled? Is the maintenance personnel likely to troubleshoot and test at the disconnect (fused or non-fused)?

If it should be labeled then per the labeling requirements of NFPA 70E 2012 it requires the arc flash boundary to be listed and that the method of calculating and data to support the information on the label be documented. Does the disconnect (say 120/240V or 480V) fall under the "Panelboards or other equipment rated >240V and up to 600V" category if you are using the tables? Can the AF boundary be safely assumed to be 30in. if the ISC is less than 25kA? Are there exceptions to this rule with disconnects of large motors where the AF boundary may be greater than this 30 inches?

Second half of this is if you are performing an arc flash analysis and the disconnect is required to be labeled (and calculations or data used to calculate documented) then does it not require that you model this equipment to calculate the arc flash boundary? Imagining that this needs to be done; then the economical impact of and arc flash study just went through the roof?? How do you weigh the economical side of things with the labeling requirements? Can the assumptions be ethically made? Can the comprehensive safety program and training of the facility personnel, if a study has been completed, just refer the staff back to 70E? Is this practical? o_O

Sorry I know there are a lot of questions here but this seems to be a "grey" area in interpretation of the standard and practicality of the analysis. I appreciate your responses.


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PostPosted: Wed Jul 10, 2013 12:37 pm 
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Joined: Mon Jan 18, 2010 11:35 am
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Location: Wisconsin
We regularly 'study and label' disconnects.
Over the past 3 years, I think we now do more often that we don't.

It is up to each individual company's Electrical Safe Work Practices program to decide what does and does not get labeled.


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PostPosted: Mon Jul 15, 2013 8:50 am 
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Joined: Mon Aug 20, 2012 10:20 am
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Location: Elgin, Illinois
FFoote, you have asked a lot of questions. So let me respond one at a time.
First of all, NFPA 70E Article 130.5(C), which was added in the 2012 Edition, specifically states that the "Electrical Equipment, such as.... that are likely to require examination, adjustment, etc...." must be field marked with a label that contains the Arc Flash boundary, Nomininal system voltage, and at least one of the following: the available incident energy at the working distance; Minimum arc rating of PPE required; Required Level of PPE; or Highest Hazard Risk Category.
Fusible Disconnect switches would fall into this category of equipment, since opening it up to replace a fuse would subject the worker to a possible arc flash situation. Non-fusible disconnect switches, however, by dictate of company policy, may never be opened to service under load, and thus, be excluded from the labeling requirement. So, the answer depends on your company's policy.


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PostPosted: Mon Jul 15, 2013 9:07 am 
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Joined: Mon Aug 20, 2012 10:20 am
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Location: Elgin, Illinois
In regards to your question about whether or not you can use Table 130.7(C)(15)(a) or (b) to determine the Hazard Risk Category and Arc Flash Boundary... etc., the answer is YES, but make sure you or someone verifies the Parameters that are listed in the table. If the Parameters are not verified, then you or your workers may not be using the proper PPE, if working on the equipment while energized. In addition to subjecting yourself or workers to possible injury, this would be a violation of OSHA's requirement to correctly assess the hazard, and provide the proper PPE for workers.


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PostPosted: Mon Jul 15, 2013 1:13 pm 

Joined: Mon Jul 15, 2013 12:35 pm
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Location: Cincinnati, Ohio
We have always supplied a label for the disconnect. Why? Because the first spot, in our experience, a maintenance person will check for a motor problem as at the local equipment or motor disconnect. Even though the disconnect, fused or unfused, may not have any "servicable parts" the maintenance person is still exposed to a arc flash occurrence when they open the disconnect and test to see if voltage is present.

We believe so strongly in this position, we do not even present a proposal for an arc flash study that does not include labeling for local disconnect means.

As far as the specifics of your questions, I defer to Ken Cybarts answers as they are spot on.


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PostPosted: Mon Jul 15, 2013 1:32 pm 
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Location: Phoenix
I appreciate everyone's input on this. Ken your thoughts are what I believe to be spot on as well. John you also bring up a good point about the practicality of things based on standard practices. I tend to strongly agree to this point as well. Dependent on the comprehensiveness of the study vs. the comprehensive safety plan used to determine case by case details. It was recently mentioned to me, that if you really get down to the details that there is no piece or electrical equipment with an access door that you cannot label per either the NFPA 70e or NEC standard. Reasoning behind this was based on the premises that everything must be assumed energized until otherwise verified. Therefore in theory an arc flash hazard still exists. For the sake of keeping the discussion rolling......Thoughts?


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PostPosted: Thu Jul 18, 2013 5:30 am 

Joined: Fri Sep 21, 2012 8:23 am
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Most of the studies I have seen do not include non-fused disconnects by reasoning that they will not require servicing while energized, while with fused disconnects they may require servicing by replacing fuses. In my opinion all disconnects should be labeled because it is very common for someone who is troubleshooting equipment to take voltage and current readings from the disconnect which is supposed to be nearby or within sight. There are recorded incidents of arc flash caused by faulty meters or using a meter at the wrong setting/ not rated for the voltage tested. The purpose of the arc flash label is for the worker to properly select the PPE. If the disconnect is not labeled then a worker can assume that there is not risk; the company just spent all this money on a thorough study (if it was done properly) and this equipment does not have a label so, therefore I do not need any PPE. I do not want a worker going into a 400amp, 480volt non-fused disconnect without a label on it.


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PostPosted: Mon Jul 22, 2013 1:26 pm 

Joined: Fri Aug 26, 2011 7:38 am
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Location: Baltimore, MD
Ken, KEC-

Even if a non-fused disconnect is never opened under load, it still might be opened while energized. A disconnect serving a machine might be opened after the machine has been turned off, and therefore be opened without interrupting the load current. However, in that scenario the switch is energized at full voltage when operated, and even after being opened, the line terminals inside the enclosure are still energized.


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PostPosted: Mon Jul 22, 2013 9:24 pm 
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Joined: Sat Apr 04, 2009 9:50 pm
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Location: San Antonio, TX
Our company has reach (with time) a compromise between economics and safety. We believe that if you include in the scope of work and survey all disconnect (fused or not) or any other electrical equipment that is fed by an OCPD of less than 100A, the cost of the service will definitely go to roof.

So after many years of experience and research, we realized that equipment fed by an OCPD of less than 100A had a low chance of having IE larger than 1.2 cal/cm2. This general rule has two exceptions. One, if the circuit fed by an OCPD is less than 20 feet from the service equipment and second, if the length of the conductor is larger than 250 feet. If a circuit satisfies these condiltions, we follow it no mater if the OCPD is less than 100A. The savings for the customer when the study is being done under this scope is SUBSTANTIAL.

Of course there might be some locations that this general rule will fail, but if it does, it will not go to much higher than 1.2 cal/cm2.
Additionally, if you want to have a perfect study where you do not have a label with a lower IE when in reality there is a higer level, you will have to survey field data with NO tolerances. Even if you are perfect on gathering data, you still have a trillion assumptions while you are performing the study. These options are called OPTIONS. Do you include the motor contribution for all motors? Or none. Do you include the decrement of the generators or not. If so, when does it start. I think you get my point.

The errors you will encounter by following this 100A or more scope are insignificant with all the errors you already have built in your present calculations. The straw in the eye of your neighbor concept.

But, as was well mentioned before, we still need to label all equipment supplied by voltages of 50V or above. And this labels now should have specific information, like IE, AFB, etc.

We still calculate and print labels for all these less than 100A electrical equipment. They happen to be the worst case. How we do this and what do we do with this "Equivalent Labels", would take more time that I have now available.

So, summarizing, all equipment have calculated labels (included all of those fed by OCPD of less than 100A). But I do not need to survey this small equipment, savings tons of money and still satisfying the standards.

By the way, we are not the only doing this. Mayor manufacturers performing arc flash studies, have a variant of this same concept.

Have a great and fantastic day!!!


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PostPosted: Sat Aug 03, 2013 4:01 am 
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Location: North Carolina
Motor contributions are not optional. But there are again some empirical rules that help drastically simplify the process and I believe some are actually listed in IEEE 1584. Generally you add together the horsepowers of all motors from 25 HP to 100 HP and treat it as one motor. All motors over 100 HP get treated individually. The cutoffs for these tend to vary a little and it all depends on how much emphasis you place on the 3rd decimal place.

I agree pretty close with the 100 A cutoff rule. Also have to consider voltage with that but generally speaking this is true, but you've also got to include the transformer in that. For instance 480 V transformers that are over 1500 kVA make it extremely difficult to achieve reasonable arc flash ratings.


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