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We can easily contact someone but they can’t do it remotely. The power company needs to come on scene. Isolating power is a lot more complex than it used to be

We can easily contact someone but they can’t do it remotely. The power company needs to come on scene. Isolating power is a lot more complex than it used to be because of solar installations. We can never be sure that every building’s solar is properly isolated from the grid. In these cases where people need to be evacuated from a vehicle that’s live due to power lines there are protocols for doing so, it’s just more risky. We need to ensure they jump from the vehicle so they’re never touching the vehicle and the ground simultaneously. We also need to get them to shuffle to make sure there’s no step potential between their feet. Neither is easy to guarantee with a member of the public probably panicking.

chrisfosterelli 5y ago
Very interesting. I hadn't considered the challenges solar could introduce to isolating power. Thanks for the answer.
- ljm 5y ago
  There's a similar problem with people using male-to-male cords (suicide cords) on their generators too? Plug a portable generator into your house this way and now it's pumping out electricity and not purely consuming it.
  - LeifCarrotson 5y ago
    It should be obvious that before you do so you should turn off the main disconnect. Otherwise you're electrifying the line for utility workers and also powering (half of) your neighbor's house backwards through a 20A circuit from your little generator, which won't work out well...
    - gpm 5y ago
      It should be obvious, but I suspect it isn't too many people... common sense isn't common.
WalterBright 5y ago
I had no idea. Are there more protocols for live vehicles? Just so I know what to do!
- dharmab 5y ago
  Ideally, stay in your vehicle and wait for help to disable the power. The vehicle's frame will protect you as long as you stay inside the car. If it's necessary to leave the vehicle (e.g. due to fire), you have to avoid being in contact with the vehicle and the ground at the same time. You have to do a funny looking hop into the air. Source: Corny energy company safety video https://youtu.be/fLVzvMTgGDY?t=168 https://youtu.be/fLVzvMTgGDY?t=168
  - WalterBright 5y ago
    thanks!
  - franga2000 5y ago
    That video has higher production value than most TV these days!
    - dharmab 5y ago
      I'm pretty sure these videos are produced to he corny so that they're memorable.
Johnny555 5y ago
We can never be sure that every building’s solar is properly isolated from the grid. Is this a new problem? Standby generators seem pretty common in the SF Bay Area - you can tell when the power goes out by the sound of generators in the neighborhood. I'd think that there are at least as many sketchy generator installs as solar installs.
- Trisell 5y ago
  You can turn a generator off, and power in lines ends. Solar is different in that there is no way to safe a panel. If it’s receiving sunlight it’s generating power. That’s a pretty different paradigm then any other electrical system currently used on buildings.
  - mrpippy 5y ago
    My understanding is that inverters are required (by electrical code among other things) to disconnect from the grid when grid power is lost. Malfunctioning (or illegally installed) inverters are possible but shouldn’t be a common problem.
    - Trisell 5y ago
      Yes, but in firefighting, a lot of the time we are up on the roof, cutting holes in the attic to let heat out of the building. The invertor will shutdown power to the inside of the building, but the line from the solar panel to the invertor is still hot. That line can be cut through as in a lot of installs it can be run through the attic. This line is never discharged but is always hot. As well as all of the lines between the panels. These can ground out in the building and cause electrical charge in objects that would be 'off' if it was a traditional power hookup that all power to the building can be shutoff from cutting the power grid building service. If one of those lines is cut, and a firefighter sticks a pike pole into the attic and touches that wire it could electrocute him just as readily as if the building was still energized by the power grid.
    - NickNameNick 5y ago
      I wonder how effective grid isolation/'anti islanding protection' is, when the 'island' is big enough, and contains multiple grid tied solar installations. It probably comes down to how they detect a grid outage. But I can think of some scenarios where the solar inverters can see each other on the grid, and assume the grid is still up
tguvot 5y ago
>We can never be sure that every building’s solar is properly isolated from the grid. I believe it's part of requirement for solar installation to stop feeding power to the grid in case there is no power from the grid.
- nostrademons 5y ago
  Yes, and this is why grid-tied solar installations go out when the power goes out. You need a battery backup for energy independence. This catches a lot of first-time solar owners by surprise if they don't do their research; they think that solar will mean they don't lose power if there's a daytime power outage, but unless they also get a battery they lose it anyway.
  - tfigment 5y ago
    You may also be restricted from exporting back to grid at all if there is battery involved by some utilities.
  - franga2000 5y ago
    Would a battery really sove that though? If regulations say that anything feeding the grid should shut down if it detects an outage of incoming power (I'm still perplexed as to how you'd measure that on the same conductor, but it's not really my field), wouldn't a battery feeding the grid have to do the same. And if you have the cut-off "upstream" of your house (so your house can still get power from the battery, but the grid doesn't), then why couldn't you do that just with the panels and no battery? Obviously a battery would be better, but in terms of cutting power in an outage, I can't see a difference.
    - andreareina 5y ago
      I imagine it's two separate inverters, a solar inverter that cannot function without grid power and a separate battery inverter. The two feeding the house circuit via a break-before-make transfer switch reduces the chances of accidentally back-feeding the grid because the isolation switch didn't work.
quietbritishjim 5y ago
> We can never be sure that every building’s solar is properly isolated from the grid. This sounds like a risk that needs to be balanced against other risks. If the fire on that bus had got to the point that it was clearly going to burn the passengers alive, it surely would have been better to allow them to walk over a possibly-electrified area? That's assuming that the responders wouldn't have needed to walk over it though.
- davidbanham 5y ago
  Yep, absolutely. Chances are if there's a going fire there won't be any isolation at all before the occupants need to be moved. In that case you try and extract them from the vehicle without letting them be shocked. Never touch the car and the ground at the same time. Shuffle away from the incident rather than walking to limit step potential.
tgsovlerkhgsel 5y ago
I'm surprised fire departments don't have equipment for emergency grounding of power lines, e.g. something that creates a ground connection and some form of launcher that throws a steel cable and/or mesh across the line. I know this exists for subway systems with a third rail, I'll edit if I find the video. Or insulating mats for evacuation, potentially with steel conductors underneath them to avoid step potential.
michaelt 5y ago
Presumably it doesn't work to just short the power cables together and let the overcurrent protection trigger?

chrisfosterelli 5y ago

Very interesting. I hadn't considered the challenges solar could introduce to isolating power. Thanks for the answer.

ljm 5y ago
There's a similar problem with people using male-to-male cords (suicide cords) on their generators too? Plug a portable generator into your house this way and now it's pumping out electricity and not purely consuming it.
- LeifCarrotson 5y ago
  It should be obvious that before you do so you should turn off the main disconnect. Otherwise you're electrifying the line for utility workers and also powering (half of) your neighbor's house backwards through a 20A circuit from your little generator, which won't work out well...
  - gpm 5y ago
    It should be obvious, but I suspect it isn't too many people... common sense isn't common.

WalterBright 5y ago

I had no idea. Are there more protocols for live vehicles? Just so I know what to do!

dharmab 5y ago
Ideally, stay in your vehicle and wait for help to disable the power. The vehicle's frame will protect you as long as you stay inside the car. If it's necessary to leave the vehicle (e.g. due to fire), you have to avoid being in contact with the vehicle and the ground at the same time. You have to do a funny looking hop into the air. Source: Corny energy company safety video https://youtu.be/fLVzvMTgGDY?t=168 https://youtu.be/fLVzvMTgGDY?t=168
- WalterBright 5y ago
  thanks!
- franga2000 5y ago
  That video has higher production value than most TV these days!
  - dharmab 5y ago
    I'm pretty sure these videos are produced to he corny so that they're memorable.

Johnny555 5y ago

We can never be sure that every building’s solar is properly isolated from the grid. Is this a new problem? Standby generators seem pretty common in the SF Bay Area - you can tell when the power goes out by the sound of generators in the neighborhood. I'd think that there are at least as many sketchy generator installs as solar installs.

Trisell 5y ago
You can turn a generator off, and power in lines ends. Solar is different in that there is no way to safe a panel. If it’s receiving sunlight it’s generating power. That’s a pretty different paradigm then any other electrical system currently used on buildings.
- mrpippy 5y ago
  My understanding is that inverters are required (by electrical code among other things) to disconnect from the grid when grid power is lost. Malfunctioning (or illegally installed) inverters are possible but shouldn’t be a common problem.
  - Trisell 5y ago
    Yes, but in firefighting, a lot of the time we are up on the roof, cutting holes in the attic to let heat out of the building. The invertor will shutdown power to the inside of the building, but the line from the solar panel to the invertor is still hot. That line can be cut through as in a lot of installs it can be run through the attic. This line is never discharged but is always hot. As well as all of the lines between the panels. These can ground out in the building and cause electrical charge in objects that would be 'off' if it was a traditional power hookup that all power to the building can be shutoff from cutting the power grid building service. If one of those lines is cut, and a firefighter sticks a pike pole into the attic and touches that wire it could electrocute him just as readily as if the building was still energized by the power grid.
  - NickNameNick 5y ago
    I wonder how effective grid isolation/'anti islanding protection' is, when the 'island' is big enough, and contains multiple grid tied solar installations. It probably comes down to how they detect a grid outage. But I can think of some scenarios where the solar inverters can see each other on the grid, and assume the grid is still up

tguvot 5y ago

>We can never be sure that every building’s solar is properly isolated from the grid. I believe it's part of requirement for solar installation to stop feeding power to the grid in case there is no power from the grid.

nostrademons 5y ago
Yes, and this is why grid-tied solar installations go out when the power goes out. You need a battery backup for energy independence. This catches a lot of first-time solar owners by surprise if they don't do their research; they think that solar will mean they don't lose power if there's a daytime power outage, but unless they also get a battery they lose it anyway.
- tfigment 5y ago
  You may also be restricted from exporting back to grid at all if there is battery involved by some utilities.
- franga2000 5y ago
  Would a battery really sove that though? If regulations say that anything feeding the grid should shut down if it detects an outage of incoming power (I'm still perplexed as to how you'd measure that on the same conductor, but it's not really my field), wouldn't a battery feeding the grid have to do the same. And if you have the cut-off "upstream" of your house (so your house can still get power from the battery, but the grid doesn't), then why couldn't you do that just with the panels and no battery? Obviously a battery would be better, but in terms of cutting power in an outage, I can't see a difference.
  - andreareina 5y ago
    I imagine it's two separate inverters, a solar inverter that cannot function without grid power and a separate battery inverter. The two feeding the house circuit via a break-before-make transfer switch reduces the chances of accidentally back-feeding the grid because the isolation switch didn't work.

quietbritishjim 5y ago

> We can never be sure that every building’s solar is properly isolated from the grid. This sounds like a risk that needs to be balanced against other risks. If the fire on that bus had got to the point that it was clearly going to burn the passengers alive, it surely would have been better to allow them to walk over a possibly-electrified area? That's assuming that the responders wouldn't have needed to walk over it though.

davidbanham 5y ago
Yep, absolutely. Chances are if there's a going fire there won't be any isolation at all before the occupants need to be moved. In that case you try and extract them from the vehicle without letting them be shocked. Never touch the car and the ground at the same time. Shuffle away from the incident rather than walking to limit step potential.

tgsovlerkhgsel 5y ago

I'm surprised fire departments don't have equipment for emergency grounding of power lines, e.g. something that creates a ground connection and some form of launcher that throws a steel cable and/or mesh across the line. I know this exists for subway systems with a third rail, I'll edit if I find the video. Or insulating mats for evacuation, potentially with steel conductors underneath them to avoid step potential.

michaelt 5y ago

Presumably it doesn't work to just short the power cables together and let the overcurrent protection trigger?