Science of Arc Flash & Engineering

[kwired]

I went to google maps and tried to look at the utility poles and transformers of USA residential.. but had difficulty finding any. Where are they located? Underground?

In my office bldg with arc flashed panel. The wires from service entrance drop to the 3 phase transformers is only 6 meters (20 feet) away (see picture below). How about in US office buildings. Is it this close too? Someone can share some pictures? The following transformers only serves my office building (just 3 units) and one storey office (1 room) besides it. POCO even let me paid for these transformers:

When it comes to available fault current though, you have a reduction at your service equipment compared to what is available at transformer terminals, as you have that 20 feet of what looks like rather small conductor, plus whatever length you have from weather head to your meter or whatever is at the bottom end of that conduit.

I don't know all the details of what you have there, but ran some calculations on a fault current calculator that is (or at least used to be) available on Mike Holt's website. I used just 75KVA single phase, transformer impedance of 2.0 (actual impedance may be higher, this is probably about worst case to expect), 20 feet of 1/0 aluminum overhead conductor then 10 feet of 3/0 copper conductor down the conduit just to give you some idea of what difference in available fault current would be from transformer terminals to your meter or main at the bottom of the conduit riser.

15625 is available short circuit current at transformer terminals.

after 20 feet of 1/0 aluminum conductors available fault current is 10805 line to line, 10024 line to neutral.

after 10 more feet of 3/0 copper conductor in steel raceway available fault current is 10097 line to line, and 8870 line to neutral.


We have gone from needing 22/25kA interrupting current gear almost to 10kA being acceptable, just a couple more feet of conductor probably puts us under 10k.

It doesn't take very much conductor distance to make a big difference in available fault current. But again current is only one piece of the puzzle of determining incident energy of an arc flash, thought it is somewhat of a big piece.

 

[tersh]

When it comes to available fault current though, you have a reduction at your service equipment compared to what is available at transformer terminals, as you have that 20 feet of what looks like rather small conductor, plus whatever length you have from weather head to your meter or whatever is at the bottom end of that conduit.

I don't know all the details of what you have there, but ran some calculations on a fault current calculator that is (or at least used to be) available on Mike Holt's website. I used just 75KVA single phase, transformer impedance of 2.0 (actual impedance may be higher, this is probably about worst case to expect), 20 feet of 1/0 aluminum overhead conductor then 10 feet of 3/0 copper conductor down the conduit just to give you some idea of what difference in available fault current would be from transformer terminals to your meter or main at the bottom of the conduit riser.

15625 is available short circuit current at transformer terminals.

after 20 feet of 1/0 aluminum conductors available fault current is 10805 line to line, 10024 line to neutral.

after 10 more feet of 3/0 copper conductor in steel raceway available fault current is 10097 line to line, and 8870 line to neutral.


We have gone from needing 22/25kA interrupting current gear almost to 10kA being acceptable, just a couple more feet of conductor probably puts us under 10k.

It doesn't take very much conductor distance to make a big difference in available fault current. But again current is only one piece of the puzzle of determining incident energy of an arc flash, thought it is somewhat of a big piece.

Thanks. I think I need to learn to compute now which is standard in the arc flash field. Will visit IEEE and other resources to know how to get the plausible incident energy taking all to those impedances, etc. into account.

 

[kwired]

Thanks. I think I need to learn to compute now which is standard in the arc flash field. Will visit IEEE and other resources to know how to get the plausible incident energy taking all to those impedances, etc. into account.

Calculator I used won't account for what is available on the high leg (which I think you have there), I just ran a calculation based on a single 75 KVA transformer, just to show you how available current drops with even relatively short conductor length.

 

[tersh]

Calculator I used won't account for what is available on the high leg (which I think you have there), I just ran a calculation based on a single 75 KVA transformer, just to show you how available current drops with even relatively short conductor length.

And it has no main breaker. If there is. And it can engage the magnetic instantaneous trip, then incident energy would be much lower. If it cant engage it and only the bi-metal strip would trip at slower 1 second, then incident energy be at least be lower too. But I guess the arc can't sustain for more than 0.5 second, so even without the bi-metal strip. The arc would self-extinguish. So if main breaker would be used. Need to make sure the magnetic strip would trip. An advance main breaker can self adjust the tripping curve to make sure it can trip on arc flash but not on nuisance transformer in rush current tripping (Getting one that works though will be the problem. If I can't get one like this. And the arc can't sustain for more than 1 sec. Then getting a main breaker that relies on bi-metal tripping won't help much, isn't it?).

But there is possibility city hall won't give permission for the main breaker because of multiple requirements and red tape. That's why 12cal/cm2 arc flash PPE suit would be good meantime just to turn on and off the breakers in the service panel, or when the POCO lineman would pull out the meter, etc.

 

[topgone]

Thanks. I think I need to learn to compute now which is standard in the arc flash field. Will visit IEEE and other resources to know how to get the plausible incident energy taking all to those impedances, etc. into account.

It's a tiresome process now with IEEE 1584-2018! So many constants to consider. The thing is they have done a series of tests at different voltages (600, 2700 and 14,300V) and they got curve-fitted formulas at each level. You also have to know how your conductors are positioned in the cubicle/work area: vertical-open air or in a box, vertical wires but opens on a barrier in a box, etc. You will have to interpolate the computed arcing current/ incident energy to the utilization voltage in your actual case (if it's 480, you interpolate the values from the 600 V test case, etc. If your case voltage falls in between; like 6.9kV, which falls in between the 2,700V and 14.300V test conditions, You have to interpolate again. The AFB is also recalculated to your own specific dimensions as the test conditions they did will be different from your specific case.

IMO, there is science there but a very circuitous one!

 

[tersh]

Calculator I used won't account for what is available on the high leg (which I think you have there), I just ran a calculation based on a single 75 KVA transformer, just to show you how available current drops with even relatively short conductor length.

I was asking about how many cycles before an arc can be considered as self-extinguishing because I'm computing for the actual incident energy at arm length. But I got a reply that says there is not much data for 120v system so I need assistance for those here like Junkhound who has done experiments on it. First the person said:
"

One of the problems that the arc flash researchers have had is predicting self-extinguishing. USUALLY it's 1 to 2 cycles maximum. But we can sort of get there through the back door. Some tests have been done with 125 VDC (not VAC) battery systems. They were able to maintain an arc for a maximum of a little under 100 milliseconds (6 cycles) with a 20 kA available fault current. In comparison and this is where we can use your data you've only got 15 kA theoretical maximum with no impedance anywhere except in the transformer. So you can never achieve 20 kA. Also that's DC where you are working with AC. Since AC has zero crossings it won't even make it for that long. I know this is a roundabout answer but there is very, very little published 120 VAC data."

​

Junkhound in msg #37 stated:

"Have done lots of arc extinguish tests over the years.
Depends on materials and initial gaps, 120V, 12000 amps fault current can keep an arc going over a 1/2" gap if aluminum, will continue until the aluminum melt away to a couple of inch gap."

Jim in msg #12 stated:

"Second, what you are asking for cannot be calculated directly. Arc Flash incident energy (AFIE) for three-phase circuits is fairly easy to calculate using formulas like those found in IEEE1584, however there are no standard industry accepted methods for calculation AFIE for single-phase circuits such as those found in a residential load center."

Isn't it that in single phase versus three phase, you use the same kVA for one transformer or do you need to add them? For example in the open delta 3 phase system:

To compute for the infinite bus assumption (ignoring all conductor impedances).. do you just use one transformer kVA (or 75kVA) for 75,000/208/0.02= 18kA value or do you use other value for the kVA (like 75kVA x 1.5x = 112.5kA)? I have asked this before but no one answered it so hope someone can answer now.

I saw the following web site to compute arc flash incident energy in IEEE 1584 2002 edition https://www.jcalc.net/electrical/arc-flash-calculator-ieee
(Let's ignore the latest IEEE 1584 2018 November edition as it was just a few months ago and very complicated as topgear stated in the last message)

I entered:

System Voltage: 208 volts
Bolted fault current: 7kA (estimating from the transformer 18kA ssc & conductor impedances)
Conductor gap: 15mm
Grounded
Working distance: 200mm (about 8" or arms length)
Arcing time: 0.016666 sec (2 zero crossings or 1/120 x 2 as it will self extinguish after this time)

Result is:

arcing current: 3.549 kA
incident energy at working distance = 0.684 cal/cm2
arc flash boundary = 142.303mm

Is the data above correct? The palm would still be exposed to 1.2cal/cm2 (less than 142mm)?


Is the formula used valid for single phase since IEEE 1584 2002 edition is only for 3 phase system?

 

[mbrooke]

Tersh, I know you wanted some US instillations. Have a look here, and also his friends' photo streams:


http://www.ipernity.com/doc/connecticut_power_lines/home/photo


Yes a lot of them are oddities or oldies like ungrounded delta systems, but there are also a lot of "typical" installations as well.

 

[tersh]

Finally received the Oberon PPE Cat 2 12cal/cm2 set for future electrical (or POCO) staff who will repair the office panel. The face shield and cap look bigger than the 3M WP96 faceshield (which doesn't have any cap):

Why didn't they make arc flash face shield clearer? It's kinda tinted. You are not looking at welding at all and normal panel. It can diminish the lights and you may need another head mounted lights.

Tried everything and face fully covered when you wear googles because of the balaclava:

I forgot to ask what are rated Arc Flash PPE underwear or what are you supposed to wear inside the PPE? I read the following warning:

"If you expose some popular synthetic fibers to even the heat of an incandescent light bulb, they will melt onto your skin. We all learned that in the 1970's disco days when this type of material first became popular. Or at least those of us over 40 did. The heat source (light bulb, cigarette lighter, or minor electrical arcing or sparking) itself is relatively harmless...maybe a 1st degree burn, that's it. BUT when the synthetic fibers melt into your skin you will receive a much more severe burn. Natural fibers char instead of melting. Also PPE is designed to keep your skin from exceeding the Stoll curve (at the face/chest area) which is generally considered around 1.2 cal/cm2. The underlayers will see that amount of heat. So what we want to do is to avoid the "work-dry" shirts, hi viz shirts, polypropylene long underwear, and other clothing underneath the PPE that can melt into the skin and do a lot more damage even if we are dressed in the correct PPE."

 

[jeremy.zinkofsky]

What good is digging into the physics of arc flash if you are ultimately going to use the infinite bus method for approximating available fault current? That calc will give you conservative approximations which can be up to 400% greater than what the utility can even contribute.

Can you get actual per unit impedance, base MVA, Voltage, etc. from the utility?

 

[tersh]

What good is digging into the physics of arc flash if you are ultimately going to use the infinite bus method for approximating available fault current? That calc will give you conservative approximations which can be up to 400% greater than what the utility can even contribute.

Can you get actual per unit impedance, base MVA, Voltage, etc. from the utility?

The 3 phase open delta transformers have 13.5kV primary and both transformers use 75kVA. I don't know the impedance.

What's puzzling is it was not supposed to happen. Remember the major arc flash was between the 208v high leg and the chassis neutral/ground. I read that "The original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result. All the other 208 V results failed because they never got to a stable arc. The original testing used 1/2" arc gaps. The new test data set used to develop IEEE 1584-2018 includes 1/4" gaps and used much thinner "fuse" wires to get stable arcing to occur down to 208 VAC. The obvious consequence here is that it is nearly impossible to have a stable arc at 1/2" (12 mm).

Yet in happened, how the hell did it happen?

This was why I was asking whether a dead bolt short can melt the aluminum lugs, caused a hole at the chassis and can they spread the debris to the surrounding that can produce a rat size 2nd degree burn in the electrician hand (this incident occurred in 2015). If dead bolt short couldn't do that. And it was arc flash. Then let it be part of IEEE data so they can do more proper tests or explanations. Digging or doing physics analysis of arm length arc flash would be complementary in the investigations. Also note IEEE 1584 was only concerned about 1.2cal/cm2 protection at 18 inches away. ​

But injury could still happen to the arms or fingers.

 

[kwired]

Isn't it that in single phase versus three phase, you use the same kVA for one transformer or do you need to add them? For example in the open delta 3 phase system:

To compute for the infinite bus assumption (ignoring all conductor impedances).. do you just use one transformer kVA (or 75kVA) for 75,000/208/0.02= 18kA value or do you use other value for the kVA (like 75kVA x 1.5x = 112.5kA)? I have asked this before but no one answered it so hope someone can answer now.

I have never been able to confirm this myself, most fault calculations, spreadsheet applications all assume three phase on a single core type transformers. I don't know how the impedance may be when you have multiple core units or banks of individual units, seems likely it will be different. That high leg has 1.5 times the winding involved in a line to neutral fault as the other two lines have to neutral. but also the other two lines to neutral are half the line to line so impedance should be less for that fault path - many spreadsheet calculators do give you both line to neutral and line to line fault current. Line to neutral is typically higher at the source and for short conductor runs, long conductor runs the resistance of conductor usually makes line to line faults higher at the end of the run.

 

[tersh]

I have never been able to confirm this myself, most fault calculations, spreadsheet applications all assume three phase on a single core type transformers. I don't know how the impedance may be when you have multiple core units or banks of individual units, seems likely it will be different. That high leg has 1.5 times the winding involved in a line to neutral fault as the other two lines have to neutral. but also the other two lines to neutral are half the line to line so impedance should be less for that fault path - many spreadsheet calculators do give you both line to neutral and line to line fault current. Line to neutral is typically higher at the source and for short conductor runs, long conductor runs the resistance of conductor usually makes line to line faults higher at the end of the run.

Hope someone can help compute.

Well. 208v arc flash is so rare even for IEEE (they had only 1 case) so hope they can take my case as example of low voltage 208v arc flash.

After looking at more pictures. I think it is 3 phase arc flash that involves all 3 phases (the other 2 just minor):

This was taken a day after the incident in 2015 inside my car:

Even the 1st lugs were affected. What could have happened was there was first a major arc flash between the
208v high leg and chassis (which even put a hole at chassis (drawn in green below) then it enveloped the area with so much heat, it progressed into 3 phase arc flash injuring the electrician arms sending him to the burn clinic:

The following with cardboard removed showing the chassis at back of first terminal was affected suggesting a 3 phase arc flash. The right chassis portion was painted.

Who is IEEE committee here. Let it become an example of a 3-phase open delta arc flash case involving 208v (in which they had only one case so far only (?)).

 

[tersh]

Finally a reference was given to me that made sense many things.

IEEE 1584-2018 was just released 4 months ago, it added changes to the 2002 edition. It addressed some of my experience but there should be additional passage that must be included especially with information like in the following about Low Voltage Arc Flash.

https://drive.google.com/file/d/0B6mGRCG7wns_bHZIRDl5VzlDSWM/view

There was a passage inside that nails it:

"In their testing without a barrier at 208 V, “arcing could not be sustained at 10 kA or less, even with the shortest (12.7 mm) gap.” A 250 V test with 13 kA of arcing current and a 12.7 mm gap extinguished at 21 ms. With a barrier, arcs were sustained down to 4.5 kA at 208 V with a 12.7 mm gap. At 32 mm arcs could not be sustained below 10 kA. Measured incident energies with the 12.7 mm gap with a 0.1 second arc and 22 kA bolted current were 2.7 cal/cm2 and it increased to 3.2 cal/cm2 for the 32 mm gap case at 22 kA. In these tests a breaker was set to open at 0.1 s so whether arcing could be sustained beyond 6 cycles is unknown."
(Remember I don't have any breaker upstream of it that can decrease the incident energy)

​

IEEE 1584-2018 tests were done using large enclosures. My arc flash breakers was enclosed in with the vertical spacing not even more than one foot. So it produced the barriers effect and others mentioned in the paper.

It was photo taken before the arc flash breaker was put at the back where the live line wires were transferred to it. The third wire was at back of the first wire so it was not visible in the picture.


I read https://brainfiller.com/2018/12/19/2018-ieee-1584-125-kva-transformer-exception-deleted/

"125 kVA – Going, going, gone!
After much speculation about the fate of the 125 kVA transformer “exception”, the 2018 Edition of IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations has finally been published and made it official. The 125 kVA transformer exception has been deleted!
In its place is the new language:

“Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A”

What Happened?
The original language is from the 2002 Edition of IEEE 1584. It was based on a few tests that indicated sustaining an arc flash at lower levels of short circuit current and lower voltage would be unlikely due to a limited conducting plasma and limited voltage to support the arc. The original 2002 language stated:
“Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply”"


Well. Instead of just “Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A” in the new 1584-2018.
The following must be added:

"Unless the panel is small in which case arcs can sustain enough to cause injuiry in the arms (at least) with higher incident energy"

IEEE 1584-2018 was just created 4 months ago. How could we let them add the above passage (or kinda like it)??

 

[tersh]

Finally a reference was given to me that made sense many things.

IEEE 1584-2018 was just released 4 months ago, it added changes to the 2002 edition. It addressed some of my experience but there should be additional passage that must be included especially with information like in the following about Low Voltage Arc Flash.

https://drive.google.com/file/d/0B6mGRCG7wns_bHZIRDl5VzlDSWM/view

There was a passage inside that nails it:

"In their testing without a barrier at 208 V, “arcing could not be sustained at 10 kA or less, even with the shortest (12.7 mm) gap.” A 250 V test with 13 kA of arcing current and a 12.7 mm gap extinguished at 21 ms. With a barrier, arcs were sustained down to 4.5 kA at 208 V with a 12.7 mm gap. At 32 mm arcs could not be sustained below 10 kA. Measured incident energies with the 12.7 mm gap with a 0.1 second arc and 22 kA bolted current were 2.7 cal/cm2 and it increased to 3.2 cal/cm2 for the 32 mm gap case at 22 kA. In these tests a breaker was set to open at 0.1 s so whether arcing could be sustained beyond 6 cycles is unknown."
(Remember I don't have any breaker upstream of it that can decrease the incident energy)

​

IEEE 1584-2018 tests were done using large enclosures. My arc flash breakers was enclosed in with the vertical spacing not even more than one foot. So it produced the barriers effect and others mentioned in the paper.

It was photo taken before the arc flash breaker was put at the back where the live line wires were transferred to it. The third wire was at back of the first wire so it was not visible in the picture.


I read https://brainfiller.com/2018/12/19/2018-ieee-1584-125-kva-transformer-exception-deleted/

"125 kVA – Going, going, gone!
After much speculation about the fate of the 125 kVA transformer “exception”, the 2018 Edition of IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations has finally been published and made it official. The 125 kVA transformer exception has been deleted!
In its place is the new language:

“Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A”

What Happened?
The original language is from the 2002 Edition of IEEE 1584. It was based on a few tests that indicated sustaining an arc flash at lower levels of short circuit current and lower voltage would be unlikely due to a limited conducting plasma and limited voltage to support the arc. The original 2002 language stated:
“Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply”"


Well. Instead of just “Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A” in the new 1584-2018.
The following must be added:

"Unless the panel is small in which case arcs can sustain enough to cause injuiry in the arms (at least) with higher incident energy"

IEEE 1584-2018 was just created 4 months ago. How could we let them add the above passage (or kinda like it)??

To add to the above comments. Reading the paper on 2nd and 3rd time and pondering on it. It was not really the panel sizes that were the factor (unless using meter enclosure that is so small because in the open tests it used one like my panel size) but whether the rods were suspended in open air without any barrier (or breakers). Why did IEEE do the 300 tests by leaving the cooper rods or wires floating in open space which were not representative of real panel with real breakers (with the top acting like barriers). What were they thinking? The IEEE tests done were flawed when taking low voltage arc flash into account ((Say, do switch gears or high voltage panels have empty spaces where the cooper tend to be hanging? How?). The paper described the barrier configuration which made so much sense as the barrier focuses the arc and incident energy to injuring proportions. Here it was described so well:


"This test uses two additional equipment configurations compared to the IEEE “standard”
configurations. The first configuration is called a barrier. Rather than leaving the copper bus bars
floating in open space like previous tests, the bus bars are “terminated” into a block of solid insulating
material such as phenolic. This is representative of the lugs on the line side of many types of equipment
such as molded case circuit breakers, and also representative of enclosures where the bus bars are
secured at one end by solid material. In this configuration the arc “plasma” tends to pool at the barrier
and jet outward, strongly increasing the incident energy as well as helping to stabilize low voltage arcs.
The second configuration is a “chamber” where part of the bus bar is enclosed in a small box within the
larger standard IEEE enclosure that is open on one side. Chambers simulate congested wireways such
as conditions where bus bars are mounted inside a lighting panel behind the circuit breakers. A chamber
both partly reflects thermal radiation as well as constraining air flow so that arcing is more stable than a
more open condition.

Arcs were not sustained at 2 kA under any conditions at a gap of 25.4 mm or up to 7 kA using IEEE
standard test conditions (copper rods mounted vertically hanging in a “chamber” or a box within a
box). Terminating the rods into a phenolic barrier allowed sustained arcing at 4 kA and using aluminum
or bars instead of rods allowed sustained arcing at 4 kA. Tests at 218 V and 250 V also showed much
more stable arcing, indicating that 208 V may be something of a limiting factor."


Therefore instead of the new IEEE 1584-2018 edition using this statement:

“Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A”


The "barrier" data must be integrated to the above.


How do you properly rephrase it?

Or could the barrier experiments be flawed in some way too?

 

[tersh]

To add to the above comments. Reading the paper on 2nd and 3rd time and pondering on it. It was not really the panel sizes that were the factor (unless using meter enclosure that is so small because in the open tests it used one like my panel size) but whether the rods were suspended in open air without any barrier (or breakers). Why did IEEE do the 300 tests by leaving the cooper rods or wires floating in open space which were not representative of real panel with real breakers (with the top acting like barriers). What were they thinking? The IEEE tests done were flawed when taking low voltage arc flash into account ((Say, do switch gears or high voltage panels have empty spaces where the cooper tend to be hanging? How?). The paper described the barrier configuration which made so much sense as the barrier focuses the arc and incident energy to injuring proportions. Here it was described so well:


"This test uses two additional equipment configurations compared to the IEEE “standard”
configurations. The first configuration is called a barrier. Rather than leaving the copper bus bars
floating in open space like previous tests, the bus bars are “terminated” into a block of solid insulating
material such as phenolic. This is representative of the lugs on the line side of many types of equipment
such as molded case circuit breakers, and also representative of enclosures where the bus bars are
secured at one end by solid material. In this configuration the arc “plasma” tends to pool at the barrier
and jet outward, strongly increasing the incident energy as well as helping to stabilize low voltage arcs.
The second configuration is a “chamber” where part of the bus bar is enclosed in a small box within the
larger standard IEEE enclosure that is open on one side. Chambers simulate congested wireways such
as conditions where bus bars are mounted inside a lighting panel behind the circuit breakers. A chamber
both partly reflects thermal radiation as well as constraining air flow so that arcing is more stable than a
more open condition.

Arcs were not sustained at 2 kA under any conditions at a gap of 25.4 mm or up to 7 kA using IEEE
standard test conditions (copper rods mounted vertically hanging in a “chamber” or a box within a
box). Terminating the rods into a phenolic barrier allowed sustained arcing at 4 kA and using aluminum
or bars instead of rods allowed sustained arcing at 4 kA. Tests at 218 V and 250 V also showed much
more stable arcing, indicating that 208 V may be something of a limiting factor."


Therefore instead of the new IEEE 1584-2018 edition using this statement:

“Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A”


The "barrier" data must be integrated to the above.


How do you properly rephrase it?

Or could the barrier experiments be flawed in some way too?

Btw.. how did IEEE 1584-2018 test the above in their 300 testing experiments. Any reference of how they exactly did it? Like did they short the 3 conductors and then turn on the main breaker to initiate the arc flash?

With 208v tests. 1 out of 300. One IEEE 1584 test case achieved a sustained arcing fault at 87 kA with a 12.7 mm gap. The rest fizzled.
When barrier (or akin to breaker) was put. Arcs were sustained down to 4.5 kA at 208 V with a 12.7 mm gap. This was quite low and likely what happened to my electrician arc flash incident in 2015.

In IEEE 1584-2018. Have they officially acknowledged the barrier tests and the data, or is there still some controversy or uncertainty about it.

208v arc flash is said to be rare in the US. How come. In office or commercial. How often do you use 208v 3 phase. Does the open delta configuration produce more short circuit current than integrated 3 phase transformers? What kind of panels were the breakers installed. Maybe no one was stupid to land any live wire to the breaker input terminal like what my electrician did in 2015, isn't it? Say, w

as my panel configuration not common in the US? In the Philippines. It's widespread.​

​

 

[mbrooke]

I think what they are saying is that at 208 volts arc flash is typically not deadly. I only say that because 208 volts tends to be supplied from smaller transformers.


I will admit I know little about the subject of arc flash, I wish I could add more

 

[tersh]

I think what they are saying is that at 208 volts arc flash is typically not deadly. I only say that because 208 volts tends to be supplied from smaller transformers.

That's right. IEEE 1584 only wants to prevent death, so they don't mind about 2nd degree burn at the arms. I was talking with the group or forum that is chairman of the IEEE 1584 draft committee and I was told essentially this concept about "Heinrich risk triangle and relative risk".

They have new 1584-2018 ruling that doesn't discount arc flash for 208v with bolted short circuit as low as 2kA (matching the small transformers). I need to know something. How many cases have you heard of arc flash arm injury only like my electrician case with incident energy that doesn't reach 1.2 cal/cm2 at the chest/are, yet about 19.2 cal/cm2 or say 18cal/cm2 at 1/4 the distance (I know it quadruples every half distance) injuring just the arm and fingers causing 2nd degree burn. IEEE ignored this because they just want to focus at the chest/face area. Or have you not heard of any arc flash injury of the arms or fingers? Imagine this typical US service entrance:

You said many US electricians work live so it's not far fetch to imagine one of them replacing the breaker live and landing the live wire from above to the lugs acccidentally causing a short to chassis creating a scenario similar to my electrician arc flash experience.

Btw.. don't worry. I won't allow my local electrician to work live anymore and the PPE suit is just for turning off or on the service breakers in case the units need repair, etc. and also perhaps for the POCO technician use in case they have to pull the meter, etc. They do it with bare hands.

I will admit I know little about the subject of arc flash, I wish I could add more

 

[mbrooke]

I've heard of electricians getting burns all over the place.


Truth be wear some gloves.

 

[tersh]

I've heard of electricians getting burns all over the place.


Truth be wear some gloves.

Burns from arch flash or electrocution/shock?

If arc flash from 208v is common, then it's widespread and IEEE focusses only on death. They should have give more warning about incident energy damage below 1.2cal/cm2 less than 18" (they only focus on face/chest area).

If arc flash from 120v residential. But these can't sustain arc flash. So from shock/electrocution where they got burn?

 

[mbrooke]

Burns from arch flash or electrocution/shock?

If arc flash from 208v is common, then it's widespread and IEEE focusses only on death. They should have give more warning about incident energy damage below 1.2cal/cm2 less than 18" (they only focus on face/chest area).

If arc flash from 120v residential. But these can't sustain arc flash. So from shock/electrocution where they got burn?

Mostly shock. But if you short circuit something like service feeders they will throw hot sparks and energy that can burn if close enough.