111–120 of 120 posts
I have been studying Grounding vs Bonding these past few weeks, great timing to see this HN discussion. Some training videos for pro electricians and US National Electric Code compliance helped me. https://youtu.be/qNZC782SzAQ Basically, bond everything together if it can carry a charge. Ground that bond at only one place in an electrical service. More than one "ground" sets up a situation where a potential differenc…
I'm actually the person who wrote this Reddit post. I'd never heard of Hacker News before, but someone messaged me on Reddit telling me this 4 year old post just surfaced over here. Let me know if you have any questions about electrical theory or installation, or anything else!
The only nit I'd pick is with the bit at the end about AC. The voltage on the neutral wire isn't due to inductive coupling, it's due to voltage drop along the neutral since neutral carries the same current as live. You'll always get this if anything's pulling significant current, earthing can't completely fix it, which is why you can't ever depend on neutral being the same voltage as earth, or as another neutral elsewhere (that's why we use dry contact relays to send signals between different pieces of kit - if they're getting neutral from different places then you can have a significant voltage difference between "neutral" in one cabinet and "neutral" in another, enough to blow up ELV gear!)
There's also the fact that, any time you use a transformer and don't earth both sides, you end up with a 'floating' AC circuit that will end up at some arbitrary voltage compared with earth. I've made this mistake before and been bitten by a stray (high impedance) 50VAC, not deadly but enough to get your attention. :P
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Except there will be no imbalance if there is no other path for the current to travel by... The geometry of the electric field in water should probably be similar to that in air (mostly contained to within the case), just don't drop both a toaster and a waffle maker in at separate ends.
Iirc gfci's are nec code allowed on non grounded lines because they will still trip, but you have to test with the gfci test button because they're only tripping on current difference, not like a breaker.
It assumes that any dangerous shocking current will be taking a path that isn't just coming back on its own white wire, presumably from taking an unspecified path to ground. This seems a reasonable assumption for safety (and the NFPA surely has looked at the data), but it doesn't really inform the above isolated-bathtub situation.
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Except there will be no imbalance if there is no other path for the current to travel by... The geometry of the electric field in water should probably be similar to that in air (mostly contained to within the case), just don't drop both a toaster and a waffle maker in at separate ends.
The resistance of slightly salty bathwater is much lower than air. While baths are not often plumbed with metal pipes these days, one can still expect some current flow to ground. It only takes milliamps of stray current to trip a GFCI.
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The US system is somewhat unique and lacks heaps of safety features: I am guessing mostly because a 110V shock is far less dangerous than a 240V shock (Although higher amperages mean higher risk of fire?). For example for UK, EU and NZ etc: sockets and pins have a variety of features to avoid touching the phase (live) wire with say a screwdriver or knife in hands of a child. For example, all new circuits installed in…
In the US there is tamper proof outlets and GFCI is equivalent to RCD. Its pretty much required for new houses though older houses may vary on what they implement.
I don't think I have ever seen a US plug where the pins have a non-conductive protective covering at the base of the pin (I think all modern UK and NZ male plugs have that. Although I'll be honest that I think the NZ solution makes plugs less safe due to risk of pins bending then breaking and leaving a live metal pin exposed in the socket).
EU sockets are mostly recessed from what I have seen (some NZ sockets are, but the recess is still is often unusable with old plugs, so is not common yet, but will become so as more plugs are sold that fit properly).
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In the US there is tamper proof outlets and GFCI is equivalent to RCD. Its pretty much required for new houses though older houses may vary on what they implement.
Are tamper proof outlets mandatory? The UK has had shutters on the phase that is opened by the earth pin forever. Which is why their plugs are caltrops, and have a plastic earth pin if double insulated (only phase and neutral wired, with no earth wire). I don't think I have ever seen a US plug where the pins have a non-conductive protective covering at the base of the pin (I think all modern UK and NZ male plugs have…
Its required by current US NEC code but older house are grandfathered in unless they do major renovation. Also some exceptions like outlets high enough to be out of reach of kids.
Its possible that the UK/NZ plugs have better designs. The code improves step by step here.
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I only brought up ground (in the Earth ground sense) because I've heard people think that antennas in general work by using the Earth as a second conductor, with EM radiation as the first. Antennas are conductors that are part of an un-closed electrical network, relying on the capacity of a conductor to hold an oscillating non-equilibrium charge (though they can be modeled as an RLC network). My previous comment was…
> The realm of electrodynamics is pretty interesting, and it's where seemingly basic concepts like electric potential begin to fail -- it becomes path-dependent! Not really. The problem is that we have sort of an "electron abstraction" which is incorrect in the Heaviside-Hertz pedagogy when fields start to store energy. I recommend "Collective Electrodynamics" by Carver Mead as a modern formulation without the sillin…
(Re "not really": with Maxwell's equations, the curl of the electric field is generally non-zero, so scalar potentials are not well-defined, which is all I meant. My experience is having gone through Purcell long ago, and by now I have some familiarity with [mathematical] gauge theory, but really I'm only an E&M dilettante.)
I'm actually the person who wrote this Reddit post. I'd never heard of Hacker News before, but someone messaged me on Reddit telling me this 4 year old post just surfaced over here. Let me know if you have any questions about electrical theory or installation, or anything else!
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Hmm okay starting to make more sense now. Do you know a good visual explanation that shows the "path" electricity takes from the transformer to your home and back out to the ground rod. Note: I fully understand in AC the electrons aren't actually moving along this path. But I guess I don't see how the circuit is ever "complete" or a circle.
This video has a great visual explanation of grounding, imho. https://www.youtube.com/watch?v=P-W42tk-fWc
Earlier quoted context omitted.
In the US there is tamper proof outlets and GFCI is equivalent to RCD. Its pretty much required for new houses though older houses may vary on what they implement.
Are tamper proof outlets mandatory? The UK has had shutters on the phase that is opened by the earth pin forever. Which is why their plugs are caltrops, and have a plastic earth pin if double insulated (only phase and neutral wired, with no earth wire). I don't think I have ever seen a US plug where the pins have a non-conductive protective covering at the base of the pin (I think all modern UK and NZ male plugs have…
No, bad design is why they are caltrops. Over here in the Netherlands shutters are similarly required but none of our plugs need a third pin. The shutter is a see-saw construction that works in such a way that you need to insert both prongs at the same time for the shutter to rotate out of the way.
That said our grounded plugs are still caltrops for no real good reason, though less so than the UK ones. They tend to fall with the prongs to the side instead of prongs-up.