NO SAFE PPE EXISTS rule
(midwest.social)
kivihiili
196An 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.
This is just... woosh.
Right over my head.
I was fine with Power Delivery, but this really doesn't need to be part of the USB standard.
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.
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?
Bah, just pucker your butt, update your will, and put on some safety squints and you'll be fine.
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
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 🤣
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/
140 if you're fancy
https://macronsafety.com/product/industrial/arc-flash-ppe/oberon-arc140b-flash-coverall-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?
😅
The mix of metric and imperial is interesting in the same measurement.
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
> Vaporized
Was not beautiful night pesis is gone
That's okay. In a few picoseconds you'll be gone two. :3
"two"
ngl, best way to go
Worth it.
391 cal/cm2 is pretty crispy lol
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.
https://e-hazard.com/how-arc-flash-energy-is-calculated/
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.
How to get crisp, fast!
