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 Post subject: Using NFPA 70E Annex F to reduce AF hazard
PostPosted: Wed Sep 02, 2009 7:06 pm 
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I have calculated and industrial electrical drives controls enclosures to be a HRC 1 on the secondary of 480/400v transformer to the first protective device. Maybe not that unusual right. But when I go the enclosure and look at the panel the circuit breaker is finger safe and the line side connections are not exposed in any way of making contact with the 400 volts on the line side of a 60 amp breaker. The load side of this breaker has a low cal/cm (.2) rating. This industrial equipment is from France so they design in some pretty good safety.

I have 3 -10 HP Digital Electronic DC drives and PLC in the same enclosure.

IS IT WRONG FOR ME TO USE NFPA 70E ANNEX F FORM TO list the precautions, risk and mitigation methods to reduce the HRC?

My understanding is the matrix indicates I can reduce the hazard to a HRC 0 for task within that enclosure. Should the form and training allow task specific work such as (e.g. connecting the computer to the PLC. viewing drive parameters, diagnostics) work for me to reduce the HRC from a 1 to a 0?


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PostPosted: Thu Sep 03, 2009 10:38 am 
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Risk and Arc Flash Studies

This is a great example of a need for Annex F. If the company owning the equipment makes the determination this is little issue. If you are a consulant you hold most of the risk (liability). In my opinion this is a reasonable application of the Risk Assessment guidelines BUT they are not really quantifiable. I would totally agree that this is a VERY low risk application and one of the reasons there are fewer arc flashes in the EU in newer equipment BUT I never take a risk to HRC 0.

Why? Because HRC 0 makes your probabality of DYING 50% if there is an ignition (2-5 cal/cm2 in most cases) BUT HRC 1 makes your chance of DYING 5%. Much better bet and VERY quantifiable.

That is the tact we take and most companies work with like the quantifiable truth. You should try a proposal on the Annex F to give it some meat and some real life examples.


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PostPosted: Thu Sep 03, 2009 12:44 pm 
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Hugh,
Thanks, I do the studies for my company only, so the risk is a little more acceptable. Saying that, I preform the task unbaised and is at times difficult for my superiors and myself.

I have already created several Annex F type forms for TASK in electronic enclosures for performing certain job functions and filed with the study results.

I have not found any post or information of others using this method in such cases. I understand that this is not a NFPA standard but seems like it should be an option in my opininion.


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PostPosted: Thu Sep 03, 2009 1:26 pm 
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Hugh,
Thanks, I do the studies for my company only, so the risk is a little more acceptable. I perform the power study task unbiased, saying that, it is at times difficult for my superiors and me to agree, but we all have our cross to bear.

I have already created several Annex F type forms for TASK in electronic enclosures for performing certain job functions and filed with the study results.

I have not found any post or information of others using ANNEX F in such cases. I understand that this is not a NFPA standard but seems like it should be an option in my opinion.

I could see were consultants would be very hesitant to use such a tool. But I believe if the consultant or engineering group doing the study would look at the physical layout of the equipment after the study and use common sense on some aspects of certain task in electronic enclosures the Annex would be useful.

Soap box sorry but I have to vent.
I would think many workers and engineers would argue the need to wear a face shield along with FR clothing while programming a drive or looking at PLC logic in an electronic enclosure. This would especially be true, when the highest hazard has been shown not too exist by design. Therefore, the problem with a lot of the electrical safety issues in my opinion the “book says†it would be safer to #%, but does it really make common sense after looking at the equipment? If the calculations say the PPE should be a #1 that’s what it is then without looking to see how the hazard exists. Yes the hazard is there if you cut into the wire while the power is on. Not while looking at a PLC. Still there are a lot of unclear issues for the industry to deal with.
Bottom line is the person doing the work should understand what they are doing and have the knowledge to make common sense of dangers. I suppose that’s not everywhere.


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PostPosted: Mon Nov 23, 2009 8:33 am 
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Looking at vs. Working On

This is a good example. "Working on" is defined in the standard (we have several slides helping folks understand what working on is). The tables do this to by defining the risk of certain tasks. Visual inspection has been added to the list of permit exempt tasks so the committee recognizes this as a lower risk task. You are doing the due diligence that companies must do if they are to do a risk assessment vs just doing calculations. Smaller companies don't have the skilled workers that the larger companies do nor the engineering support so they can't reasonably do a hazard/risk assessment. It is important for the standard to make this a clear difference. The tables are trying to do risk and hazard assessment for the general, small company population. This is the tough part. Larger companies with knowledgable "electrical" safety people can do risk assessments internally and make their decisions.


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PostPosted: Mon Nov 23, 2009 12:27 pm 
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Thanks, Hugh. We have been missing you. Glad your back.


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PostPosted: Mon Nov 23, 2009 1:31 pm 
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Clothing or PPE

Yeah, I love reading on here but I run two companies, Arc-Wear does clothing testing and e-hazard does electrical safety training. Don't get out in the forum's as much as I'd like. Let me know if you see something I could add value on. Zog let's me know about critical questions.

Jim, Mr. Brainfiller himself if a great resource. Love this tool.


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