4 ms·

This is called equipotential bonding and a failure to implement or maintain it leads to occasional but tragic or fatal outcomes, we had one recently locally whe

This is called equipotential bonding and a failure to implement or maintain it leads to occasional but tragic or fatal outcomes, we had one recently locally where a 12 year old girl was seriously brain damaged and needing life long care because she touched an outdoor tap.

segfaultbuserr 7y ago
This possibility is obvious from the technical documents I read, and it was what I worried (and I'm still worrying!) about. Thanks for the comment, I now know it's a real danger, not just a theoretical one. Because of this, I eventually abandoned the mesh network experiment. I don't want to blow the school up and pay for it, and potentially have someone killed, just for a faster Intranet. And I decided that if I'm going to do the experiment in the future, I'll just setup a gateway in an open space, somewhere middle but away from the buildings (so the gateway can pick the signals from those buildings), and run the system on solar power. In this case, lightning protection becomes easier - just ground the system and it should be fine.
petre 7y ago
That's probably why the two faucets in the UK are required to be electrically bound with a counductor, under the wash basin or sink. If the mains is in contact with a pipe and not the other, touching both faucets would result in electrocution. Also an extra argument for a single combined faucet for both cold and hot water.
- tomohawk 7y ago
  Even if you use non-metallic pipes like PEX?
- gpderetta 7y ago
  Separate faucets for cold and hot water is one of those inexplicable British things for an immigrant like me.
  - vorpalhex 7y ago
    When hot water was retrofitted in many homes, it was stored in an open top basin which would collect rats and whatnot. Thus the cold water was kept separate in order to be more clean. Why any newer install has it though, nostalgia?
  - jdsnape 7y ago
    it was inexplicable for me as a native too - although I recently discovered that it was specified by older regulations as they were worried about contamination between the hot and cold-water supplies. The hot water supply was traditionally fed from a header tank in the loft (attic) and so wasn't safe to drink.
    - gpderetta 7y ago
      > The hot water supply was traditionally fed from a header tank in the loft (attic) and so wasn't safe to drink. Now that I think of it, I have the same setup in my flat. The tank is supposedly sealed, but I'm not sure how reliable the seal is (it is not a pressurized tank).
    - willyt 7y ago
      In older houses there is only one tap it is ‘safe’ to drink from. Usually in the kitchen, all others, hot and cold, are fed from the tank in the roof. For some reason it’s OK to brush your teeth with water from the tank but not to actually drink it.
    - Gibbon1 7y ago
      A British coworker said he thinks it's because authorities were worried about the water supply being intermittent. A rooftop tank solves the contamination back flow issue via an air gap. And provides water when the mains aren't working. I also suspect the British would have found a old school US style water heater to be somewhat frightening. https://www.youtube.com/watch?v=AVK6bkj5Ug4 https://www.youtube.com/watch?v=AVK6bkj5Ug4
  - DenisM 7y ago
    I assumed it was a money-saving measure. If you have separate faucets you can't get warm water, only cold and/or hot. So to get warm water you're forced to fill in the sink and make use of that, which saves both water and heating.
- vonmoltke 7y ago
  Hot and cold faucets in the UK are physically separated? Every such unit I have seen in the US has a common brass manifold for both valves.
- nwallin 7y ago
  No, the real reason had nothing to do with electricity. In fact dual taps were entrenched before electricity was common place. Mythbusters have done several demonstrations over the years of what happens when you take a hot water heater, disable both of the over pressure valves, and break the thermostat so that it doesn't turn off. They explode spectacularly. Early water heaters had zero overpressure valves. And thermostats are not particularly reliable even today. So exploding a home wasn't particularly uncommon. In the UK, they made a low tech solution to this problem. Look in your toilet, in the back. There is a level sensor. If there is insufficient water, more is added. Imagine taking a large one of these and putting it in your attic. When you drain out of it, gravity provides the pressure. Now put a heater under it attached to a thermostat. If the thermostat fails, either you have cold water (failed closed) or boiling water in your attic and there's fucking steam everywhere (failed open) but you notice and shut it off. If the level sensor fails, you either get water pouring into your house and you turn it off, or the hot water turns off and you investigate. Under no circumstances can pressure build up and explode the house. Of course in like the 1880s better safety mechanisms were developed so it's fucking ludicrous it's still like this but whatever I'm not the king of england. edit: I forgot the punch line. These are open top devices so all manner of shit got into your hot water. They kept separate taps to ensure that when you were pouring cold water for food, you knew it was clean and not contaminated with your hot water. Why they're ok with showering in shit water is something you'd have to ask a Brit.
  - spiznnx 7y ago
    Your edit is very interesting and explains why my mother (who lived in the UK from 11-25) ingrained in me as a child to let the water run cold for a while after switching from hot before drinking. She said it was due to increased rust in the longer hot water path, but I suspect that it is mostly culturally ingrained due to your explanation and the rust explanation is just working backwards
  - mark-r 7y ago
    That explains a bit from Fawlty Towers where Manuel kept complaining about a pigeon in the water tank. Never quite got that before.

segfaultbuserr 7y ago

This possibility is obvious from the technical documents I read, and it was what I worried (and I'm still worrying!) about. Thanks for the comment, I now know it's a real danger, not just a theoretical one. Because of this, I eventually abandoned the mesh network experiment. I don't want to blow the school up and pay for it, and potentially have someone killed, just for a faster Intranet. And I decided that if I'm going to do the experiment in the future, I'll just setup a gateway in an open space, somewhere middle but away from the buildings (so the gateway can pick the signals from those buildings), and run the system on solar power. In this case, lightning protection becomes easier - just ground the system and it should be fine.

petre 7y ago

That's probably why the two faucets in the UK are required to be electrically bound with a counductor, under the wash basin or sink. If the mains is in contact with a pipe and not the other, touching both faucets would result in electrocution. Also an extra argument for a single combined faucet for both cold and hot water.

tomohawk 7y ago
Even if you use non-metallic pipes like PEX?
gpderetta 7y ago
Separate faucets for cold and hot water is one of those inexplicable British things for an immigrant like me.
- vorpalhex 7y ago
  When hot water was retrofitted in many homes, it was stored in an open top basin which would collect rats and whatnot. Thus the cold water was kept separate in order to be more clean. Why any newer install has it though, nostalgia?
- jdsnape 7y ago
  it was inexplicable for me as a native too - although I recently discovered that it was specified by older regulations as they were worried about contamination between the hot and cold-water supplies. The hot water supply was traditionally fed from a header tank in the loft (attic) and so wasn't safe to drink.
  - gpderetta 7y ago
    > The hot water supply was traditionally fed from a header tank in the loft (attic) and so wasn't safe to drink. Now that I think of it, I have the same setup in my flat. The tank is supposedly sealed, but I'm not sure how reliable the seal is (it is not a pressurized tank).
  - willyt 7y ago
    In older houses there is only one tap it is ‘safe’ to drink from. Usually in the kitchen, all others, hot and cold, are fed from the tank in the roof. For some reason it’s OK to brush your teeth with water from the tank but not to actually drink it.
  - Gibbon1 7y ago
    A British coworker said he thinks it's because authorities were worried about the water supply being intermittent. A rooftop tank solves the contamination back flow issue via an air gap. And provides water when the mains aren't working. I also suspect the British would have found a old school US style water heater to be somewhat frightening. https://www.youtube.com/watch?v=AVK6bkj5Ug4 https://www.youtube.com/watch?v=AVK6bkj5Ug4
- DenisM 7y ago
  I assumed it was a money-saving measure. If you have separate faucets you can't get warm water, only cold and/or hot. So to get warm water you're forced to fill in the sink and make use of that, which saves both water and heating.
vonmoltke 7y ago
Hot and cold faucets in the UK are physically separated? Every such unit I have seen in the US has a common brass manifold for both valves.
nwallin 7y ago
No, the real reason had nothing to do with electricity. In fact dual taps were entrenched before electricity was common place. Mythbusters have done several demonstrations over the years of what happens when you take a hot water heater, disable both of the over pressure valves, and break the thermostat so that it doesn't turn off. They explode spectacularly. Early water heaters had zero overpressure valves. And thermostats are not particularly reliable even today. So exploding a home wasn't particularly uncommon. In the UK, they made a low tech solution to this problem. Look in your toilet, in the back. There is a level sensor. If there is insufficient water, more is added. Imagine taking a large one of these and putting it in your attic. When you drain out of it, gravity provides the pressure. Now put a heater under it attached to a thermostat. If the thermostat fails, either you have cold water (failed closed) or boiling water in your attic and there's fucking steam everywhere (failed open) but you notice and shut it off. If the level sensor fails, you either get water pouring into your house and you turn it off, or the hot water turns off and you investigate. Under no circumstances can pressure build up and explode the house. Of course in like the 1880s better safety mechanisms were developed so it's fucking ludicrous it's still like this but whatever I'm not the king of england. edit: I forgot the punch line. These are open top devices so all manner of shit got into your hot water. They kept separate taps to ensure that when you were pouring cold water for food, you knew it was clean and not contaminated with your hot water. Why they're ok with showering in shit water is something you'd have to ask a Brit.
- spiznnx 7y ago
  Your edit is very interesting and explains why my mother (who lived in the UK from 11-25) ingrained in me as a child to let the water run cold for a while after switching from hot before drinking. She said it was due to increased rust in the longer hot water path, but I suspect that it is mostly culturally ingrained due to your explanation and the rust explanation is just working backwards
- mark-r 7y ago
  That explains a bit from Fawlty Towers where Manuel kept complaining about a pigeon in the water tank. Never quite got that before.