Approach Boundary...

[CEDEng]

Regarding NFPA70e and similar - please push me to a different forum (topic) if there's a better place...thanks in advance for any insight...

Just using a generic example, say 50kV - NFPA70e says 8' to exposed circuit parts.

What if my "exposed circuit part" is inside of a fence? Is it still "exposed?" Considerations about fence height, gap size, and material come to mind - but if a "fence" isn't good enough to say "it's no longer exposed" - then why is a transformer case good enough? And so on...

Bottom line - we're trying to protect a prototype / test area with a fence. Safety people insist on putting it at the approach boundary - which means a minimum room size of 16 foot square, plus test (usable) area. A normal "barricade" - say, a rope-line or tensa - is not meant to prevent access - and is not capable of preventing access - so 8' still makes sense. Not so, with a tall tight fence.

So - does my test area need to be 8' from the INSIDE of my fence? Any reference in NFPA (or other) where I can at least have the conversation?

 

[paulengr]

Regarding NFPA70e and similar - please push me to a different forum (topic) if there's a better place...thanks in advance for any insight...

Just using a generic example, say 50kV - NFPA70e says 8' to exposed circuit parts.

What if my "exposed circuit part" is inside of a fence? Is it still "exposed?" Considerations about fence height, gap size, and material come to mind - but if a "fence" isn't good enough to say "it's no longer exposed" - then why is a transformer case good enough? And so on...

Bottom line - we're trying to protect a prototype / test area with a fence. Safety people insist on putting it at the approach boundary - which means a minimum room size of 16 foot square, plus test (usable) area. A normal "barricade" - say, a rope-line or tensa - is not meant to prevent access - and is not capable of preventing access - so 8' still makes sense. Not so, with a tall tight fence.

So - does my test area need to be 8' from the INSIDE of my fence? Any reference in NFPA (or other) where I can at least have the conversation?

Ok a couple different issues here. First off 70E does NOT apply. It stops at 15 kV. You should be using NESC.

Second is that the definition of exposed means not insulated, guarded, or accessible. So if it’s 12 feet in the air it’s not accessible. If it has a fence around it, so you cannot INADVERTENTLY touch it or get too close it’s guarded. In 50 kV gear the spacing is around 12-15” internally. That’s far less than 8 feet.

Third dovetailing on my last point since you are talking high voltage, critical flashover distance between any conductor and the energized parts is critical. Must exceed this distance. Also the stuff nearby like a fence needs to be grounded or it becomes energized via induction. That is why utilities ground all their fences often with a thick in insulated copper cable or busbar bonded every few inches to the fence and connected to a ground grid.

In high voltage, “insulated” also means properly shielded or its only covered not insulated (creep). And everything needs to have a specific voltage established, no floating equipment.

By way of example large transformer plants have extensive fencing around all of their test cells with locks and often interlocks.

 

[jim dungar]

Ok a couple different issues here. First off 70E does NOT apply. It stops at 15 kV. You should be using NESC.

That is not true.

The IEEE1584 calculations for arc flash incident energy stop at 15kV, but NFPA70E has shock hazard boundaries well above that level and there are other methodologies that can be used for arc flash.
Unless you are a utility (public or private), I think you would have a hard time convincing OSHA that the NESC applies to you. Of course, you may include some components of the NESC into your Electrical Safe Work Practices program, but you cannot ignore NFPA 70E simply because you have voltages in excess of 15kV.

 

[paulengr]

That is not true.

The IEEE1584 calculations for arc flash incident energy stop at 15kV, but NFPA70E has shock hazard boundaries well above that level and there are other methodologies that can be used for arc flash.
Unless you are a utility (public or private), I think you would have a hard time convincing OSHA that the NESC applies to you. Of course, you may include some components of the NESC into your Electrical Safe Work Practices program, but you cannot ignore NFPA 70E simply because you have voltages in excess of 15kV.

Then why did they DELETE everything above 15 kV and state this as a cutoff starting around 2015 or 2018 edition with regards to arc flash.

Ok, quiz time. Which electrical maintenance standard does OSHA reference in Subchapter S? Give up yet? IEEE 516 the standard for working on outdoor overhead energized lines. In 2006 OSHA fined GM based on lack of ANY standard with regards to arc flash hazards. They do not mandate any particular standard so you can adopt whichever one makes sense.

That being said OSHA, NESC, and 70E have one thing in common: they ALL reference IEEE 516 for shock protection. Except that 516 has 3 different work methods: rubber glove, insulated tools, and bare hands. 70E only recognizes one: rubber glove method. Rubber glove method is only available up to 40 kV. After that you have to use hot sticks or bare hands. So already we don’t have a valid work method for testing for absence of voltage, REQUIRED by OSHA. Also in numerous places 70E specifically requires doors closed and latched because the whole standard is based around typical industrial enclosed equipment. So how does it apply to OPs situation? It doesn’t.

Also NESC is indeed used for generation, transmission, and distribution. A big part of the standard is for overhead lines but it is far more general than that. It is far more applicable to equipment testing labs which use a variety of open, exposed gear which has far more in common with generation plants than enclosed gear plants.

What I’m suggesting is to apply the most applicable standard. 70E copies an overhead line standard but the scope precludes 50 kV equipment.

 

[jim dungar]

Then why did they DELETE everything above 15 kV and state this as a cutoff starting around 2015 or 2018 edition with regards to arc flash.

NFPA70E is much more than just arc flash, it is about safe work practices when working with energized equipment.
The NESC is for public and private utilities not industrial and commercial locations.

There are several, OSHA approved, methods available for checking absence of voltage with out having to make direct contact with energized components. Two of the polpular ones are:

https://www.panduit.com/content/dam/panduit/en/landing-pages/verisafe/D-SFCB13--SA-ENG-VeriSafeHazloc-PB-W.pdf

Salisbury 4356 Complete Audio / Visual Voltage Detector Kit • Sales, Rent, Calibration, & Repair at JM

Salisbury 4356 Complete Audio / Visual Voltage Detector Kit, 1-4244 Tester 240V to 230 kV with Case and Shotgun Adapter

jmtest.com

Each employer needs to create, maintain, enforce, and be ready to defend their own Electrical Safe Work Practice (ESWP) program. These programs should reference applicable standards from sources like NFPA and IEEE among others. Of and by itself NFPA70E is not an ESWP.

 

[paulengr]

First off the OP is way off track. The 8 foot boundary is for the limited approach boundary. The table itself comes from IEEE 516. See annex A. This table is a common source of confusion.

To begin with if we erect a fence or solid wall (grounded!) the conductor is no longer accessible. Looking at the 70E tables, what is the limited or restricted approach boundary without exposed conductors? Zero. The approach boundaries disappear. The limited approach boundary for a 120 V plug is 3 foot 6 inches. Using your safety persons definition of this guarded plug the plug would have to be 3 foot 6 inches radius or over seven feet in diameter!

The limited approach boundary isn’t even in IEEE 516 though. It is commonly referenced in OSHA 1910.269 as well as NESC but never named. It is the point where we need to stop movement on unqualified personnel from exposed conductors.

Looking further the restricted approach boundary is only 3 foot 3 inches. This is called the minimum approach distance in IEEE 516. It consists of an inadvertent movement adder of 2 feet PLUS the actual flashover distance. So the actual minimum flashover distance in this standard is only 15 inches.

But we are in the realm of equipment design here. For a solid grounded panel we should look at IEEE 510 which is the standard for high voltage and high power test equipment. Grounded covers should be placed at least 1 inch per 7500 Volts or 6.7 inches away. So there is your solid plate clearance.

Going a step further there are various standards for the IEC “test finger” for finger safe equipment. The mechanical finger itself is 80 mm long or 3.2 inches so with punched plate or louvers with finger sized holes we are up to 9.9 inches. On an fence the holes are larger and the fence flexes which is much harder to determine. I would add at least 2 to 3 inches. As you can see we are very close to the IEEE 516 15 inch distance.

 

[paulengr]

NFPA70E is much more than just arc flash, it is about safe work practices when working with energized equipment.
The NESC is for public and private utilities not industrial and commercial locations.

There are several, OSHA approved, methods available for checking absence of voltage with out having to make direct contact with energized components. Two of the polpular ones are:

https://www.panduit.com/content/dam/panduit/en/landing-pages/verisafe/D-SFCB13--SA-ENG-VeriSafeHazloc-PB-W.pdf

Salisbury 4356 Complete Audio / Visual Voltage Detector Kit • Sales, Rent, Calibration, & Repair at JM

Salisbury 4356 Complete Audio / Visual Voltage Detector Kit, 1-4244 Tester 240V to 230 kV with Case and Shotgun Adapter

jmtest.com

Each employer needs to create, maintain, enforce, and be ready to defend their own Electrical Safe Work Practice (ESWP) program. These programs should reference applicable standards from sources like NFPA and IEEE among others. Of and by itself NFPA70E is not an ESWP.

You are only looking very superficially at scopes. I wrote the public inputs removing the 40 cal “limit” (informational note) and removing the silly UL 61010 reference for a voltage testing procedure when the correct standards are IEC. The UL standard is for meter design not test procedures.

NESC, OSHA 1910.269 snd 70E all contain the same shock shock table. All of them refer to IEEE 516 which is the original source for energized work procedures. IEEE 516 has three work methods over all: rubber glove method, insulated tools (hot sticks), and live line bare hands. At one time all of them had all three methods. However 70E deleted hot sticks and bare hands. The highest class rubber gloves only go to class 4 or 36 kV. The Salisbury detector can’t be used bare handed. So 70E can’t be used;

70E also requires closed doors. It is designed for enclosed industrial style equipment. This is open style equipment, identical to the NESC use case. Second strike.

And although the 70E tables go to 15 kV maximum and used to reference NESC which goes much higher, the reference was deleted. Strike three.

NESC is different from NFPA in that NFPA breaks out the electrical standard into 4 volumes but NESC combines them into one. But it covers all equipment from 50 V to over 500 kV including not just overhead lines but also generation plants which are as industrial as it gets.

 

[jim dungar]

I have no problem with an ESWP that refers to applicable portions of standards like NESC, however unless the employer is a utility, NFPA 70E should generally not be ignored.

There is a huge difference in the training and work procedures for utility workers, which are reflected in the NESC, versus non-utility workers subject to NFPA 70E.

 

[paulengr]

I have no problem with an ESWP that refers to applicable portions of standards like NESC, however unless the employer is a utility, NFPA 70E should generally not be ignored.

There is a huge difference in the training and work procedures for utility workers, which are reflected in the NESC, versus non-utility workers subject to NFPA 70E.

That is absurd.

The exact same training is required for utilities. Everyone receives hazard recognition and avoidance training, everyone. Some workers receive training in energized work methods and procedures. They are qualified on those procedures to perform work with hazards present. It doesn’t matter what type of industry it is.

Further, in a letter of interpretation regarding an industrial plant that had a cogen, OSHA stated that the difference between 1910.269 and subchapter S has nothing to do with SIC Codes. It has everything to do with the type of equipment. Generation, transmission, and distribution follows 1910.269. Utilization only follows 1910.300-399. Construction follows 1926. 70E only implements procedures for 1910.300-399. NESC covers all of it but terminology is different and the prohibition on energized work is not as strict.

I also worked at a site with a mine, barge facility, air strip, locomotives, cogen, and chemical plants. ALL Codes applied but other than terminology and some minor rules like the prohibitions I’m energized work and LOTO variations they are largely identical. As an example construction (1926) requires tagout but locks are optional. 1910.269 requires tagout always and locks in most but not all cases. Mining requires tags and locks. 1910.300-399 requires locks but tags are optional. Keep in mind there are 4 LOTO procedures under .269, 3 under .300-399, 1 under mining (3 copies), and 1 under 1926 as examples.

 

[CEDEng]

Wow - I leave the thread alone for a day and look what happens! Ok - a small clarification - or maybe fuel for the fire...

With regard to NFPA70e - this standard (per the scope) provides guidance for electrical safety in the workplace. That is the focus of my question, so if it helps to ease the situation, I'll concede to a circuit less than 36kV. However - I initially used my 2018 copy - Table 130.4 (D) - for the information. If that part is sourced from another standard - it changes nothing for me. I just know that the distances listed there are commonly referred to by "The Safety Folks" and so that is what I'm referring to.

I completely understand that the "approach" boundary is aimed at "exposed" circuits. The question is: At what point is a fence good enough to say "it's not exposed?" Some folks (I believe incorrectly) feel that a fence is the same as "nothing." If my fence is infinitely high and the spacing is very tiny, then surely this is good enough. If my fence is 3 feet high, and made like a rail fence around the pasture - eh, not so good.

Regarding the hazards of flashover, distance, grounding, and so forth, if using reduced clearances - this not a utility or other application. It's a prototyping and HV lab. Voltages may be high. Withstand / Dielectric testing can reach 50kV or more. And at that moment - ALL the conductors are exposed, including the device under test. There is a decent argument to be made that (in some cases) the available current is simply not enough to be fatal - but we cannot use that as a guide. We shall assume the worst - and that's what triggers the approach boundary.

Hope that helps! Thanks everyone for the great info so far.

 

[paulengr]

Wow - I leave the thread alone for a day and look what happens! Ok - a small clarification - or maybe fuel for the fire...

With regard to NFPA70e - this standard (per the scope) provides guidance for electrical safety in the workplace. That is the focus of my question, so if it helps to ease the situation, I'll concede to a circuit less than 36kV. However - I initially used my 2018 copy - Table 130.4 (D) - for the information. If that part is sourced from another standard - it changes nothing for me. I just know that the distances listed there are commonly referred to by "The Safety Folks" and so that is what I'm referring to.

I completely understand that the "approach" boundary is aimed at "exposed" circuits. The question is: At what point is a fence good enough to say "it's not exposed?" Some folks (I believe incorrectly) feel that a fence is the same as "nothing." If my fence is infinitely high and the spacing is very tiny, then surely this is good enough. If my fence is 3 feet high, and made like a rail fence around the pasture - eh, not so good.

Regarding the hazards of flashover, distance, grounding, and so forth, if using reduced clearances - this not a utility or other application. It's a prototyping and HV lab. Voltages may be high. Withstand / Dielectric testing can reach 50kV or more. And at that moment - ALL the conductors are exposed, including the device under test. There is a decent argument to be made that (in some cases) the available current is simply not enough to be fatal - but we cannot use that as a guide. We shall assume the worst - and that's what triggers the approach boundary.

Hope that helps! Thanks everyone for the great info so far.

I’ve been to the test cells for repairs and maintenance for SPX and ABB. SPX in particular has a BIL tester that goes to 2 million Volts...artificial lightning! Our own test stand stops at 12.47 kV during power testing but we can hi pot up to 50 kV if needed. TuV is about 2 miles away and UL is about 30 miles away if we need more.

The approach boundaries apply to EXPOSED conductors. If you restrict anyone’s ability to touch the component this is called guarding and that is what a fence does. If it is guarded, it is NOT exposed. At that point there is no limited or restricted approach boundary. At that point throw everythjng about approach boundaries out.

The problem when you do this though is that you have to look at three things. The first is opening size and shape. The IEC test finger is designed for this purpose. You can build/buy one for complex shapes but it is overkill for a simple guard. Google “IEC test finger” with images and you get plenty of detailed dimensioned drawings, suppliers, etc. If the openings are small enough so you cannot get your hand through then the 80 mm finger is all the extra distance to be concerned with.

The second with a flexible guard like a fence it can flex and bow. So unless it is something more rigid than chain link fence you have to somehow measure how much it bows. This is where a metal perforated plate like the kind that the safety fence people sell to use with strut is much better...it is rigid and comes in nice colors. The kind of thing you see around a robot manufacturing cell.

The grounding requirement is in NEC 250.190 and 191.

The required distance for test labs is in IEEE 510. In fact the whole safety requirement for what you are doing is in there. Simplifying its 1 inch per 7500 Volts.

 

[jim dungar]

That is absurd.

Yes denigrating, or at the least dismissal of, NFPA70E, certainly is.

 

[CEDEng]

Thank you Paulengr, very astute comparisons.

It's been my experience that some plant "safety folks" have a tight grasp on what is required, because they are responsible for a narrow area, and "tested" into the position. (I use "test" loosely.)

Other places - well, the "safety folks" are responsible for everything from snow on the sidewalk to paper cuts at the copier. These folks mean well - doing the best they can do - but it's not reasonable to expect they know the ins and outs of every relevant standard (although some do).

Thank you all for the answers - which back-up my own logic: A fence precludes the need for an approach boundary, within the limitations of the fence, the gaps, the grounding, and so on...but, probably, the "footage" in NFPA70e is no longer part of the discussion.

Great forum, as always, thank you!