The new requirement in 110.24(A) c

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MBLES

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is this usualy done by the engineer or designer? if a electrical contractor is performing work does he hire an engineer? please if someone can provide some feed back..
 
This rule in the 2014 NEC does not really require the services of an engineer. You get the available fault current from the utility. They typically give the current at the secondary side of their transformer. You may have to do some calculations to get the available fault current at the service equipment. Bussmann has a nice app that will let you do that calculation if necessary.

Often, if the available fault current at the transformer is less than the short circuit rating of the service equipment, the number from the utility is posted on the equipment without doing the calculation for the cable between the transformer and the service equipment.

This will change in 2017 if the first draft stands...the proposed rule will require a full arc flash calculation.
 
There are calculators that will help with the arc flash design - they are based on distance from transformer, transformer ratings, conductor material ,sixe, conduit used -- a plug & play type calculator so that the equipment fit within the parameters designated.
 
ron said:
That would be interesting. Especially since the line side of the service disconnects are tough to calculate without clear input from the utility on their upstream protection.
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I can't even get a load side terminals available fault current figure from most POCO I deal with:(

Hard enough to just find out what transformer impedance is in most cases and when I do such calculations I am often using an assumed transformer impedance along with assuming infinite supply capabilities.


I have mixed feelings on NEC requiring the marking of arc flash energy levels.

Most of what I install is frequently serviced (to some extent) by non qualified personnel. Such markings mean nothing to them, available fault current means nothing to them. For that matter "High voltage" and possible arc flash hazards doesn't even register if they see it. Now if you are a qualified person and working in an environment where you use 70e or other safety standards those markings have a meaning, and are already required by such safety standards. So to an extent this is just NEC pushing itself into protecting the untrained again - even though they don't really understand anyway.

Don't get me wrong I am not against the safety aspect, just that 70e already covers this kind of thing. If a worker doesn't understand the simple and already required "potential arc flash" labels what good is it to further break down the hazard level? They either are using 70e and will shut down when working on it (likely will suit up to verify it is dead if they do use 70e) or they are not using 70e and will not wear anything specifically for protection.

A good qualified person also knows to some extent that if they are at the end of a long run, or at a location with smaller source that the levels are somewhat low, and also knows if there is a larger source that the closer they are to that source the higher the incident energy will be (in general).This comment has little to do with whether or not such markings are needed - just a statement that those that are qualified will have some idea of what is going on, and a non qualified person has no clue in this area.
 
kwired said:
A good qualified person also knows to some extent that if they are at the end of a long run, or at a location with smaller source that the levels are somewhat low, and also knows if there is a larger source that the closer they are to that source the higher the incident energy will be (in general).This comment has little to do with whether or not such markings are needed - just a statement that those that are qualified will have some idea of what is going on, and a non qualified person has no clue in this area.
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At the end of a long run, you may often have lower short circuit current and cause typical inverse time protective devices to act slower, often leading to much higher incident energy, because the device trips slower in the short time region, long time region or never.

Not always intuitive to a good qualified person
 
ron said:
That would be interesting. Especially since the line side of the service disconnects are tough to calculate without clear input from the utility on their upstream protection.
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Yes, I understand that is the most difficult point on the system to get the required information to do an arc flash calculation, but the following is from the first draft report.
110.16(B) Service Equipment.In addition to the requirements in (A), service equipment shall contain the following information:
  • Nominal system voltage
  • Arc flash boundary
  • At least one of the following:
    • Available incident energy and the corresponding working distance
    • Minimum arc rating of clothing
    • Site-specific level of PPE
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luckylerado said:
It is my opinion that this is additional CYA to protect you from the stupid. Not the stupid from an arc flash.:slaphead:
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Does the average person who would benefit from this label, understand what any of the information presented on it even means?

Other than nominal voltage, I know I don't really understand the rest of it. And I've learned how to do this calculation.
 
luckylerado said:
It is my opinion that this is additional CYA to protect you from the stupid. Not the stupid from an arc flash.:slaphead:
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How am I assured the information on the label is accurate to begin with? Codes may require that new calculations be made when certain changes are made - but as mentioned earlier it is often hard to even know what the impact is on the POCO primary side - and even if we do know, they can change things at any time and then the labels are incorrect.

Carultch said:
Does the average person who would benefit from this label, understand what any of the information presented on it even means?
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Exactly my argument against such labeling. Maybe things are different in different parts of the country, but around here nearly nobody would understand any of that information other then those that do the calculations. (I won't even say those that affix the label necessarily understand). Go to an industrial plant where they have fairly complex safety program (especially including electrical safety and use of 70e) and maybe it is useful, everywhere else around here it is the contractor, designer, and/or electrical inspector that pay any attention to such labels. May be a poor attitude to take on this topic but that is the reality I am seeing.

In the past 15 -20 years I only recall once seeing a service person put on a hood/face shield to work on something live, have seen gloves put on for performing certain tasks several times, but that is about it. Until we see more people using "proper PPE" those labels are fairly meaningless.
 
A Better Way to Label

A Better Way to Label

I did some work for my municipal water treatment facility this week. They seem to have a better handle on things than the NEC.

Saw this label on a valve. I think it could be adapted for electrical.

mail.google.com.jpg
 
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