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Correct in every case. PPE is the last line of defence against either your fuckup or an unavoidable case of shit hitting the fan.
The first defence is using the squishy meat goo in your skull to not catch a case of avoidable death.
“This machine has no brain, you must use your own” being one of my favourite comedic warning labels
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An arc flash can literally melt your PPE in to your skin. The only safety worth a damn is not letting it happen in the first place.
I was fine with Power Delivery, but this really doesn’t need to be part of the USB standard.
This is just… woosh.
Right over my head.
well, in short, this electrical transformer lowers the input voltage by 26 times, but because of P = VI (power = volts × amps) the amps must go up by 26 times, and P = I2R (power dissipated (heat output) = amps squared × resistance, assuming R is constant) makes them become very very violent in an arc fault (kinda like a short circuit; the power gets concentrated in one place) on the secondary (“output”) side.
in reality its a bit more complicated and R is probably not going to be constant but either way that little 2 means you are going to have a very bad time if this secondary (which is almost certainly supplying gobs of power) has an arc fault.
the 391 cal/cm^2 and “Flash hazard at 18 in” means that if you have your hand 18 inches (45 cm) away from the secondary, it is estimated that every square centimeter of something (skin) exposed in the direction of it will receive 391 calories of energy in an arc fault. one calorie is the amount of energy needed to heat one milliliter (1 cm3 of water) by 1 degree celcius.
dividing out the cm2, this means that such an arc fault has enough energy to theoretically heat your exposed skin up uniformly by 391 degrees celcius to a depth of one centimeter. again, reality differs—it will not be exactly 391 calories, it will not be uniform, and your skin will be beyond burnt!
of course, that’s not even getting into the explosions and stuff that would also take place that result in the “NO SAFE PPE EXISTS” label, where PPE is personal protective equipment.
the solution to eliminating the hazard here if you absolutely must get near this transformer is to turn it off (deenergize it) so you don’t need the PPE. but there have been some interesting situations in history with immensely hazardous objects that were deemed necessary to approach and couldn’t be disabled, where it was dangerous to the point those around simply didn’t wear PPE because it would do nothing. the harvey casino bomb comes to mind!
Wow, thank you for this in-depth explanation! :3
It all sounds very dangerous to me, tbh.
Arc flash incident energy IS the explosion. That’s the size of it. Anything over 40cal is considered dangerous (no PPE exists)
The distances are based on the covers being off as opposed and someone working on it. NOT during normal operation. It is generally safe to be near electrical equipment if it is not being worked on/opened up.
I wish the NFPA70E would put more guidance on transformer labelling. I believe there should never be 2 conflicting labels especially when the 2 dangers cannot be isolated (such as a transformer, like this). Say the secondary side was 39kcal, you’d want an arc flash suit rated for that (with everything: balaclava, hood, pants, shirt, and of course natural fibers underneath and preferably AR 8kcal daily wears) - the secondary side being 480v would call for class 00 gloves to protect from shock, but if you accidentally touched the hot side, you’d be fried. The only arc flash label on a system like this should say class 2 gloves to protect you against the high side and it should say the maximum incident energy (39kcal from the secondary) with the associated approaches based on highest voltage and arc incident of the entire enclosure, since it cannot be isolated.
But, its also a transformer, there is no reason why one should ever be opened live, except to verify absence of voltage. I do believe that transformers should all be required to have isolated bus terminations/integrated disconnects so that you can verify absense of voltage prior to opening though…that will take some time to catch up. But in the mean time every transformer should at minimum have line of site dedicated disconnects to each transformer primary side.
But, its also a transformer, there is no reason why one should ever be opened live, except to verify absence of voltage.
Maintenance consultant who has not set foot on site writes a report recommending condition based maintenance including thermal imaging on all electrical equipment and didn’t bother to see if it comes with an IR window… Hopefully this sticker convinces the boss to give up that plan.
I mean, all that thermal imaging is really doing is checking for hot spots. Just follow NFPA70B to find when you should be performing PMs on this transformer. But really the thermal imaging would tell you to tighten some bolts. Why not just clean the contacts and tighten the bolts? That’s a shit consultant - recommending people try to kill them self to see if a bolt is loose is dumb. Turn the thing off and tighten the bolt.
An IR window won’t tell you if the windings are going bad, and that’s much more critical than the terminations. With the transformer de-energized, do a winding ratio test at the frequency recommended by NFPA70B, while you’re tightening bolts.
The fucked up part is that maintenance consultant probably gets pedigree by commenting on the NFPA concensus review sessions to advocate for his way. Feel free to PM me if you need help getting that fucker walked off site. I love throwing the code book at people that try to kill maintenance workers.
It was a hypothetical situation, don’t worry. Not really outside of the realm of things I’ve seen 🫠
I think it depends a lot on how critical the system is and what the risk of failure is. I work in critical infrastructure and we aren’t going to rely on a code minimum PM schedule. We don’t want to run our transformers to failure, even if we have redundancy, because lead times are fucking crazy right now. Like, more than a year. You are limited in terms of shelf spares due to space and storage/exercise requirements.
I’m not an electrical person but our electrical maintenance department seems to be on board with condition based maintenance so there must be some benefit to them. We do require IR windows and other features on equipment that allow the tests to be done safely. Apparently the IR windows are easy to retrofit.
The other benefit is tracking trends over time. Some of the offline analysis (like the winding ratio) you mentioned will give you data, but you can check more things and more frequently with the windows. You can see when a particular bus connection is slightly warmer than the others, for example, and decide to take it down sooner than required to have a look and correct.
It’s a different situation than what we are describing but we recently had a motor failure and one of the three phases was getting slowly hotter over time (we had online trends) until it shorted and kablamo! No one was monitoring those temps but we sure are now lol.
That makes sense. I shouldn’t have bashed IR windows. The plants that mandate rigid conduit everywhere, IR windows make sense and are good. For the limited budget plants, I think IR windows on transformers are low priority. But infinite budget, IR windows are great.
IR windows have a lot more use cases outside of transformers where I think they are more important. And everything has to do with frequency and down time availability.
The last job I worked was a steel mill. I was in charge of all electrical distribution from utility to disconnect prior to production equipment. Because of the metal dust, we needed to vacuum out distribution equipment yearly at a minimum and NFPA70B recommended some tasks yearly for us. I left when my 2 day outage on a 3 day weekend was canceled. I consolidated the outage plan to a single day, and they still wouldn’t let me have it. Once we got a year behind, I left. I’ve been gone a year, and they still haven’t done it.
I had the main transformers on a 5 year EOL plan because of oil samples and age. The lead time was 18 months for each, and they needed 3, lol. The EOL plan was also neglected.
I would’ve felt more comfy with IR windows lmao but I wasn’t going to stick around to be the scape goat when the plant goes down.
I worked in chemical manufacturing before infrastructure and there is no way in hell I’m going back to anything that isn’t strictly regulated lol.
Not that we don’t get our fair share of nonsense, but manufacturing is a whole other world of crazy.
Ha I feel that. Manufacturing is fun as fuck but kinda ridiculous and sometimes stupid dangerous
This is the kind of comment where when I (clueless) read it, after the second sentence, the third is reduced to a stream of words bouncing around in my mind
The ELI5 of my comment:
I would rather work on something that’s 13,000 volts as opposed to something that’s 480 volts. Because 13,000 volts is a bad shock if I fuck up. Whereas 480 volts could be a bomb going off in front of me, not because I fucked up, but because it could just spontaneously combust (not entirely true, but I’ve seen plenty of arc flash incidents where it doesn’t seem like anything happened but all of a sudden an electric panel blows up).
If you’re morbidly curious, emphasis on morbid, feel free to look up some arc flash videos. They’re crazy big explosions when bad. Fucking scary to see the aftermath of, let alone to be apart of.
Anyways, the NFPA is the governing body of electric. Arc flash wasn’t talked about in the electric code till like the 90s, so its a relatively new discovery, in an already relatively new industry (vs say food prep/food code). There’s a lot that needs to be learned and improved upon.
Transformers take one voltage and make it a different voltage in the same box. The code doesn’t have a standard way of labelling the arc flash hazards, which means you get stupid things like the original picture.
If you read the top label it tells you to wear thick (class 2) gloves and as long as you do that you’re safe. The bottom label tells you if you work on the equipment, there is no level of ppe that can protect you. Both labels are technically true for what they’re talking about. But someone without experience might stop after the first label, put on gloves and then get vaporized in a catastrophic explosion. In my comment I pretended that the explosion level was 39kcal (instead of 391) because there is a safe level of PPE that would protect someone from an explosion that big - it’s basically a bomb suit - just gloves wouldn’t keep you safe. The gloves the bottom label tells you to wear wouldn’t keep you from getting shocked though. So you would want to wear the top label’s gloves and the bottom labels bomb suit to be fully safe.
The code books don’t standardize how to communicate the required PPE which makes people do stupid things like in this picture: show conflicting requirements for safety. Shitty labeling like this can kill someone, but its not necessarily wrong labeling because the code leaves it up to interpretation.
Transformers take one voltage and make it a different voltage in the same box. The code doesn’t have a standard way of labelling the arc flash hazards, which means you get stupid things like the original picture.
The primary and secondary can be in different enclosures. I agree the sticker config does not make sense for something with two enclosures.
I do think your explanation is a little off, even if it is in one enclosure. Shock hazard and arcflash hazard analysis is independent, as are the PPE requirements. You need to account for both when planning work. The Shock hazard PPE only looks at the voltage of the system (see table 130.7©(7)(a)) whereas arcflash PPE needs to be suitable for the incident energy at the distance they will be performing their task. There is no overlap in the assessment.
The pictured stickers are kind of shitty because they do not clearly show that Arcflash and Shock hazards are different types of hazards and different types of incidents.
I’m more used to stickers like the one shown on this handy guide: https://www.70econsultants.com/Downloads/RozelLabelPosterv8.pdf
Here we have the primary side saying if you are more than 26" away you aren’t required to wear shock protection PPE (restricted approach) but that you are still at risk of 2nd degree burns from an arc flash within 30" . You can still get shocked up to the limited approach (60") but you aren’t required to wear PPE. Approach boundaries are from table 130.4(E)(a). This distance is consistent with an exposed circuit at the given voltage (rather than a moving contactor).
Additionally, incident energy is calculated at the distance the worker would be from the arc source when performing a task. That is why the primary side has the incident energy at 36" which is outside of the boundary, and why the 0 class (no protection) is indicated. And why you need to read the report and not just rely on the stickers! It would list the tasks and how everything is calculated.
On the secondary side the restricted approach is 12", again consistent with the table in NFPA70E. In terms of arc flash it is saying the worker would be 18" from the source when doing the work, and that it is impossible to do safely. We don’t know the particulars of the design of this transformer so we can’t say why it’s 36" on one side and 18" on the other. The secondary sticker is basically saying there is no safe way to work live, regardless of shock protection, because the arcflash incident energy is too high.
The code books don’t standardize how to communicate the required PPE which makes people do stupid things like in this picture: show conflicting requirements for safety. Shitty labeling like this can kill someone, but its not necessarily wrong labeling because the code leaves it up to interpretation.
I also disagree with this. The code specifies that you must meet both the Arcflash and the Shock hazard PPE requirements if you are within the specified distances (130.7©(1) a and b). If it’s in one enclosure you are subject to the Arcflash PPE within the boundary radius of the arcflash source, and there is no way you are outside of the radius for the secondary side when working on the primary side. Discussion of gloves is moot because we are not taking the cover off this thing, but they are required to do the analysis anyways.
Workers are not meant to rely only on the stickers. It’s the last line of defense and meant to be a sanity check on site. The workers in charge are required (by the code) to complete a job safety plan for each work task. If you come to site and your work plan has different boundaries than on the stickers, you know something is wrong.
The primary and secondary can be in different enclosures.
Thus is true. In which case the labels should be applied to the separate enclosures.
I agree the sticker config does not make sense for something with two enclosures.
Glad we agree.
Shock hazard and arcflash hazard analysis is independent, as are the PPE requirements. You need to account for both when planning work. The Shock hazard PPE only looks at the voltage of the system (see table 130.7©(7)(a)) whereas arcflash PPE needs to be suitable for the incident energy at the distance they will be performing their task.
I agree with all of this. The nuance I’d add is that PPE needs to be suitable for the shock and incident energy they could receive while performing their task. The common field example would be the controls guy working on their low voltage DC inside a box with exposed 480v. Even if they 480v is further than 42" away from the control part they’re working on, they should still be wearing gloves. Similar with arc flash boundaries. For my guys, I consider the arc flash danger to be a plane parallel to the enclosure door as opposed to a single part, which goes above and beyond NFPA70E, but is becoming more and more industry standard/consensus. Basically, if you enter an enclosure you need protection for all exposed parts.
The secondary sticker is basically saying there is no safe way to work live, regardless of shock protection, because the arcflash incident energy is too high.
I don’t think I disagreed with anything prior to this statement. But this is where your argument starts to fall apart. The arc flash boundary for the secondary side is 613 inches, or 51 feet. Since the labels are both placed on the outside of a single enclosure, and moreover, they are placed together (as opposed to one clearly on the primary side and one clearly on the secondary side). Because we don’t live in a fantasy land, we can assume that the transformer is not 51’ in any direction.
This means that there is no working condition where you could be safe while working on the primary side and NOT exposed to the secondary side.
PPE is the last line of defense. Administrative, engineering, etc. all come before PPE. And one of the biggest causes of error is human error. Meaning designs should be designed to limit human error.
While drawings are important to look at, the reality is that not every maintenance worker will look at drawings. And especially during an outage or failure, steps are more likely to be skipped. To reduce errors, arc flash and shock hazard stickers should not have different information they should only list the highest required PPE or highest determination of PPE (as in highest voltage, and highest arc flash potential) of all internal components. It’s the same reason why MCCs and Distribution panels should only have one label - despite having breakers that technically have different incident energies. Oddly enough, the debate of placing different stickers only seems to exist around transformers (with some exceptions where distribution panels have cabinets that could isolate arc flash potential).
The reality is that the stickers are technically a higher level of protection than simply PPE. They should be clear, and they should give clear direction. I cannot enter the primary side of this transformer without being exposed to the arc flash potential of the secondary side, so there is no reason to list the arc flash boundary of the primary side. The arc flash boundary of the transformer is the higher of the 2 boundaries, and it should be labelled as such. Similarly, you need class 2 gloves to protect you from the guts of the transformer. A transformer is one single device and should be treated as such. Control boxes have 480v and low vDC, we don’t go into the cabinet with no PPE just because we’re working on vDC.
I do applaud the training of your plant though, it sounds like your guys have more awareness than many plants I’ve seen. But even with that training, you are introducing human error factors when you label like this.
I think we are agreeing.
When I said
The secondary sticker is basically saying there is no safe way to work live, regardless of shock protection, because the arcflash incident energy is too high.
I meant
there is no working condition where you could be safe while working on the primary side and NOT exposed to the secondary side.
It sounds like you all don’t have task specific job safety plans? I’m not blaming you, it’s a systemic problem at the management level. Elec is basically the only team that does this well tbh and I think it’s because the supervisor does not fuck around and will not take a management no for an answer. It helps that we are unionized.
We have plans for routine work come out with work orders for PMs and we will do them for correctives as correctives come up and keep them on file.
Let’s say we get a new equipment. We require the arc flash study before it’s delivered. We make sure it matches up with our expectations and then it will be used to create PMs. Like you said, there is no reason to work on this live so no PMs or correctives would have the team working on it live and they would all include switching orders and how to verify it has been deenergized. Anyone opening a panel without all that is getting sacked, and we make sure they know it.
I should also be clear this isn’t my plant and we don’t label like this. It’s not a great label but I can see why someone did it (to show it was calculated for both sides) we especially if they are some fresh out of school engineer 😅
No formal training, just good at finding the guy who likes to yap and following him around so I can learn all I can.
It sounds like you all don’t have task specific job safety plans?
Depends where I’ve worked, what the task is, and how it’s structured.
Data center? Yes, we had quadruple redundancy. Boring job.
Auto plant? PMs, yes. Reactive? Sometimes, but if the line was down, we weren’t getting them printed out. The maintenance training program was incredible though, trained the troubleshooting process, even the dumbest could have written a work plan for any piece of equipment. All equipment had PPE requirements and showed LO locations and procedures. For reactionary work, work plan was quick chat with everyone involved, then follow SOP for de-energization, verify de-energization. The work was done up front similar to how you’ve described, but on every team. Nothing got missed.
100 year old steel mill? PMs and only sometimes. Fun place to work, but that job was almost 100% fire fighting. Safety culture didn’t exist, especially when private equity took over lol. Early on had an untrained maintenance guy in street clothes operate a tripped breaker rated over 90 cal, he did not look to see what caused trip. That was when I was able to create a glove and training program lol. But that plant is the biggest reason why I’m against double labels. That plant hasn’t filled my position, and when I left, very little of it got delegated. The arc flash stickers are probably the last line of defense, I don’t think the drawings have been looked at since I left. That’s common in a lot of plants I visit at my new job, unfortunately.
I’ve had arguments with arc flash study providers over it - unfortunately this isn’t necessarily a dumb new engineer - these are well seasoned vets. And double labels in a book, or on a drawing makes sense. But when you look at plants that do less than bare minimum safety, it highlights how important those stickers are. The well trained facilities with good safety culture will have drawings to get information that’s missed on the removed label (primary side incident energy). But safety culture can go to shit overnight, turnover, etc. Sticking with 1 label per enclosure ensures that the safety you provide on those stickers will outlast your program.
Labeling requirements per NFPA70E are nominal voltage, arc flash boundary, incident energy or PPE category*, and minimum PPE requirements. I believe that minimum PPE requirements should be carried through entire enclosure, and adding that to the book would close the transformer debate. But I think its been unaddressed for too long that they should be adding a note specifically calling out transformers and DPs.
*this requirement is why you’ll see a PPE level listed instead of a PPE category if the incident energy is precisely calculated
Wouldn’t 13,000 volts be the bomb going off compared to the 480?
Or do you mean “a bad shock” as in you die instantly and so you don’t really experience the arc flash?Great question, but nope, 480 is the bomb going off.
If you’re familiar with Ohm’s law then pick a consistent number for power and calculate the current for both voltages.
If you don’t know Ohms law, imagine if you wanted to move the same amount of water as a river moves through a hose, you’d find the water from the hose would fuck you up a lot more than the water from the river. Similar principal with current.
The transformer shown in the picture is likely one of the most dangerous devices in the plant, because it’s taking all that river and shoving it into a hose (turning 13kV into 480v while maintaining the same power). Because of that, the incident energy (explosion size) is at it’s highest at the 480v side of the transformer (current is at its highest).
The only protection (such as a breaker/fuse) upstream of the 480v side of the transformer is on the 13kV side. Imagine the river was shoved into a hose via a water fall. Imagine you wanted to turn the river off because someone was getting blasted with the hose, you’d have to run up a waterfall, which would lower your response time. During which the person getting blasted by the hose would continue to get blasted with the hose.
Transformers almost always have a breaker or fuse directly after it in a circuit, so that it can regulate and respond in a faster way to things such as an arc flash. But the transformer is generally where you see the highest incident energy. That is coming directly from the 480v side. But aside from verifying that the transformer is de-energized there is literally no troubleshooting or manual task that would warrant operating on it live.
Arc flash is not the same as shock. Arc flash is literally an explosion. I’ve been on-site for minor ones that stay contained in the box and just leave smoke and molten metal in the box. And I’ve been there for ones that literally blast the panel front off till it hits a wall - those are the scary ones. Luckily that one no one was nearby it when it blew up. It happened from vibrations moving dust between contacts. The shrapnel would hurt, but even worse is the potential to heat flash the inside of your lungs. That’s why when operating 480v equipment you should take a deep breath first to fill up your lungs, so that you don’t accidentally fill your lungs with hot as fuck air.
However, I would much rather get SHOCKED by 480v over 13,000 volts. But I’d rather not get shocked, so I wear proper gloves for the voltage I’m working on.
Shock and arc flash are different hazards that have different causes and risk analysis. They are independent of each other, but you must meet the PPE requirements for both when working within the respective boundaries.
I talked to a guy once who said he had shorted out 480v to a copper busbar. This vaporizes a bit of the copper, which then condenses in your skin, which is very painful. He also said he had the taste of metal in his mouth for the next entire year.
277V hurts bad too. Its angry and spiteful and makes sure you remember it.
230 just makes my tummy flutter a little like butterflies
Yeah 120/240 isnt bad unless its got a sizeable load. Just surprises you and makes you replace your strippers 🤣
Yeah if it short circuits there’s no PPE for tens of thousands of amps anywhere near your body.
POV: you just pulled down your botgirls pants
> Go to town on that robussy
> VaporizedWas not beautiful night pesis is gone
That’s okay. In a few picoseconds you’ll be gone two. :3
“two”
3
ngl, best way to go
putting a new spin on “arc flash” ;)
Worth it.
The PPE tops out at 100 cal. Transformer secondaries are so high because there’s no breaker or fuse to trip, you have to wait for the primary side protection to trip and that might take a while.
https://macronsafety.com/product/industrial/arc-flash-ppe/100cal-arc-flash-suit/
The suit is not intended for use as a bulletproof vest.
This is so American
The window and suit tested to a V50 of 712 ft/sec with a ballistic threat using a .22″ fragment, and 789 ft/sec with a .308″ fragment.
It is an understandable clarification to include.
What will they think of next
Paying for remote racking?
😅
Bah, just pucker your butt, update your will, and put on some safety squints and you’ll be fine.
The mix of metric and imperial is interesting in the same measurement.
391 cal/cm2 is pretty crispy lol
that seems like a very high current system?
Only on the secondary side of the pictured transformer. The primary is very low current, but high voltage, whereas the secondary is low voltage (480v) high current.
So doing the math, 26 amps at 480VAC. So 12.5kW of power. Power was using simple DC equation so it could be better or worse, excuse my rusty knowledge.
Where did the 26 amps come from?
The amount of ouch is on the label: 391 cal/cm2
True I just got off work and I wasn’t reading properly, I seemed to confound 1.0 cal/cm2 with amps in my excitement, and forgetting it is also RMS and not stated here.
Hey it’s OK to not know what you’re looking at…480v is the RMS voltage, but it really doesn’t have much to do with this.
This is an arc flash label. It tells you how big a boom a piece of electrical equipment can make.
It is based on many factors, not just voltage, power, and amperages. It factors in equipment sizes and gaps, locations in the system, etc. to generate a model of how much boom it can go.
How to get crisp, fast!
