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.
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.
It's probably from America. You don't want your grad student doing unit conversions in their head when they're being subjected to unsafe levels of radiation.
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!
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.
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.
36 replies
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"
3Worth 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/
140 if you're fancy
https://macronsafety.com/product/industrial/arc-flash-ppe/oberon-arc140b-flash-coverall-suit/
This is so American
It is an understandable clarification to include.
Is it for resistance to chunks of metal flying off in the case of an explosion?
What will they think of next
Paying for remote racking?
😅
391 cal/cm2 is pretty crispy lol
The mix of metric and imperial is interesting in the same measurement.
It's probably from America. You don't want your grad student doing unit conversions in their head when they're being subjected to unsafe levels of radiation.
Bah, just pucker your butt, update your will, and put on some safety squints and you'll be fine.
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!
Wow, thank you for this in-depth explanation! :3
It all sounds very dangerous to me, tbh.
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.