3 ms·

Is this actually unsafe? In theory, won’t the circuit breaker flip if the load ever becomes unsafe? ISTM, this might end up being inconvenient (Plug another Com

Is this actually unsafe? In theory, won’t the circuit breaker flip if the load ever becomes unsafe? ISTM, this might end up being inconvenient (Plug another Computer into the UPS, and the breaker flips), but it won’t be dangerous, unless someone also “upgraded” the breaker.

HarryHirsch 6y ago
unless someone also “upgraded” the breaker That happens. 10 years ago or so there was a big explosion at the University of Texas, Austin. The Chemistry Department had a storage vessel for liquid nitrogen. Of course the cold liquid evaporates and creates pressure inside the container. Typically the internal pressure is held at 1.5 bar by means of an escape valve. The escape valve failed and someone replaced it with a solid brass plug. To prevent accidents if the escape valve fails there is also a burst disk that breaks at higher pressure but before the tank itself explodes. That mechanism worked as designed, it released pressure, so they replaced the emergency release valve with a brass plug as well. One nice night the burst pressure of the tank itself was exceeded, and the bottom launched itself through the floor. The top was stopped by a concrete beam, but it did break a few water pipes. Here's the report from the Fire Marshal: https://www.tdi.texas.gov/fire/documents/fmred022206.pdf https://www.tdi.texas.gov/fire/documents/fmred022206.pdf There is no need to test if safety equipment works, because sometimes it does not.
- c1ccccc1 6y ago
  The terrible thing is that this happened in a chemistry lab, where people should really know better. Liquid nitrogen is dangerous in a surprisingly large number of ways: Cold burns when touched, explosions when sealed in a container. And if you're in an enclosed space with it, you've got to be careful not to let it fill the room with nitrogen gas and asphyxiate you.
  - HarryHirsch 6y ago
    in a chemistry lab, where people should really know better Some places are accident factories, where people are encouraged to be team players and not rock the boat even in the face of clear and present danger. Universities can be problematic, when you do your PhD you really need your supervisor to give you a good recommendation.
sbierwagen 6y ago
Circuit breakers are not guaranteed to trip quickly for currents just slightly above their rating. Take the look at the trip curve for a QOB120, an unremarkable residential circuit breaker: https://download.schneider-electric.com/files?p_enDocType=Tripping+curves&p_File_Name=730-3.pdf&p_Doc_Ref=730-3 https://download.schneider-electric.com/files?p_enDocType=Tr... The top end of the graph is labeled 10,000 seconds. If there's a marginal wirenut connection between the breaker and the powered equipment, you may not want to give it 2.7 hours to heat up, possibly catching fire. After a century of experience, we now design electrical systems with multiple overlapping safety systems. That photo of the plug shows an earthing pin, after all. That pin does nothing, and is not required for the device to function. It is only there in the event a connection fails and a live wire touches the metal case of the equipment. This is rare, but if you tour the parts of the internet featuring accidental deaths, bad grounding is an entire category of video. Think of it as a code smell. It not an error, and won't prevent the equipment from working. But it's not good.
- petee 6y ago
  I trust the chart because of the source...but my own experience differs - if I'm reading that right, it's saying that it would take 20 seconds upto a max of 400s at 2.5 times rated current: that's 50 amps up six minutes? I have a hard time believing that. Pump 20a though any breaker you find it trips nearly immediately
  - namibj 6y ago
    You may want to take a look at the circuit breaker characteristics: https://en.wikipedia.org/wiki/Circuit_breaker#Standard_current_ratings https://en.wikipedia.org/wiki/Circuit_breaker#Standard_curre...
    - petee 6y ago
      Thank you, I did, but it doesn't exactly make it any clearer
  - petee 6y ago
toast0 6y ago
It's not uncommon to have several 15A outlets on a 20A breaker. So if you plug a 20A load into this thing, I would expect the outlet to overload and fail, but the current through the breaker might not be enough to trigger it.
Godel_unicode 6y ago
What are the odds that someone willing to do something this sketchy only struck once? I can practically hear them saying "wires are wires" while putting a bigger breaker in...
ThrustVectoring 6y ago
Electrical wiring is designed to operate safely even if one thing goes wrong. If this is the only out-of-code thing then yeah, it'll be fine. "One mistake away from serious issues" is a policy with a body count, though.
- nucleardog 6y ago
  If power bars and all other manner of plug splitters didn’t exist If we didn’t already put up to 12 (!!) outlets on a 15A breaker (where I live, anyway — trying to find some US numbers online it sounds like there is no limit there?!) If you couldn’t trivially create a 24A load on a kitchen plug by plugging two small appliances in on your counter Then I would agree. As it stands, this is no more dangerous than the things that literally hundreds of millions of monkeys in as many homes and offices are doing every day by accident.

HarryHirsch 6y ago

unless someone also “upgraded” the breaker That happens. 10 years ago or so there was a big explosion at the University of Texas, Austin. The Chemistry Department had a storage vessel for liquid nitrogen. Of course the cold liquid evaporates and creates pressure inside the container. Typically the internal pressure is held at 1.5 bar by means of an escape valve. The escape valve failed and someone replaced it with a solid brass plug. To prevent accidents if the escape valve fails there is also a burst disk that breaks at higher pressure but before the tank itself explodes. That mechanism worked as designed, it released pressure, so they replaced the emergency release valve with a brass plug as well. One nice night the burst pressure of the tank itself was exceeded, and the bottom launched itself through the floor. The top was stopped by a concrete beam, but it did break a few water pipes. Here's the report from the Fire Marshal: https://www.tdi.texas.gov/fire/documents/fmred022206.pdf https://www.tdi.texas.gov/fire/documents/fmred022206.pdf There is no need to test if safety equipment works, because sometimes it does not.

c1ccccc1 6y ago
The terrible thing is that this happened in a chemistry lab, where people should really know better. Liquid nitrogen is dangerous in a surprisingly large number of ways: Cold burns when touched, explosions when sealed in a container. And if you're in an enclosed space with it, you've got to be careful not to let it fill the room with nitrogen gas and asphyxiate you.
- HarryHirsch 6y ago
  in a chemistry lab, where people should really know better Some places are accident factories, where people are encouraged to be team players and not rock the boat even in the face of clear and present danger. Universities can be problematic, when you do your PhD you really need your supervisor to give you a good recommendation.

sbierwagen 6y ago

Circuit breakers are not guaranteed to trip quickly for currents just slightly above their rating. Take the look at the trip curve for a QOB120, an unremarkable residential circuit breaker: https://download.schneider-electric.com/files?p_enDocType=Tripping+curves&p_File_Name=730-3.pdf&p_Doc_Ref=730-3 https://download.schneider-electric.com/files?p_enDocType=Tr... The top end of the graph is labeled 10,000 seconds. If there's a marginal wirenut connection between the breaker and the powered equipment, you may not want to give it 2.7 hours to heat up, possibly catching fire. After a century of experience, we now design electrical systems with multiple overlapping safety systems. That photo of the plug shows an earthing pin, after all. That pin does nothing, and is not required for the device to function. It is only there in the event a connection fails and a live wire touches the metal case of the equipment. This is rare, but if you tour the parts of the internet featuring accidental deaths, bad grounding is an entire category of video. Think of it as a code smell. It not an error, and won't prevent the equipment from working. But it's not good.

petee 6y ago
I trust the chart because of the source...but my own experience differs - if I'm reading that right, it's saying that it would take 20 seconds upto a max of 400s at 2.5 times rated current: that's 50 amps up six minutes? I have a hard time believing that. Pump 20a though any breaker you find it trips nearly immediately
- namibj 6y ago
  You may want to take a look at the circuit breaker characteristics: https://en.wikipedia.org/wiki/Circuit_breaker#Standard_current_ratings https://en.wikipedia.org/wiki/Circuit_breaker#Standard_curre...
  - petee 6y ago
    Thank you, I did, but it doesn't exactly make it any clearer
- petee 6y ago

toast0 6y ago

It's not uncommon to have several 15A outlets on a 20A breaker. So if you plug a 20A load into this thing, I would expect the outlet to overload and fail, but the current through the breaker might not be enough to trigger it.

Godel_unicode 6y ago

What are the odds that someone willing to do something this sketchy only struck once? I can practically hear them saying "wires are wires" while putting a bigger breaker in...

ThrustVectoring 6y ago

Electrical wiring is designed to operate safely even if one thing goes wrong. If this is the only out-of-code thing then yeah, it'll be fine. "One mistake away from serious issues" is a policy with a body count, though.

nucleardog 6y ago
If power bars and all other manner of plug splitters didn’t exist If we didn’t already put up to 12 (!!) outlets on a 15A breaker (where I live, anyway — trying to find some US numbers online it sounds like there is no limit there?!) If you couldn’t trivially create a 24A load on a kitchen plug by plugging two small appliances in on your counter Then I would agree. As it stands, this is no more dangerous than the things that literally hundreds of millions of monkeys in as many homes and offices are doing every day by accident.