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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
POV: you just pulled down your botgirls pants
> Go to town on that robussy
> Vaporized
ngl, best way to go
Was not beautiful night pesis is gone
That's okay. In a few picoseconds you'll be gone two. :3
"two"
3
Worth it.
putting a new spin on "arc flash" ;)
Yeah if it short circuits there's no PPE for tens of thousands of amps anywhere near your body.
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 🤣
I was fine with Power Delivery, but this really doesn't need to be part of the USB standard.
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
Is it for resistance to chunks of metal flying off in the case of an explosion?
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.
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.
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.
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.
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(C)(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(C)(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.
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.
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.
391 cal/cm2 is pretty crispy lol
The mix of metric and imperial is interesting in the same measurement.
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.
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 = I^2^R (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 cm^3^ of water) by 1 degree celcius.
dividing out the cm^2^, 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!
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.
Wow, thank you for this in-depth explanation! :3
It all sounds very dangerous to me, tbh.
Bah, just pucker your butt, update your will, and put on some safety squints and you'll be fine.
How to get crisp, fast!
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.