If your house gets 800V DC you're still gonna need "bricks" to convert that to 5VDC of 12VDC (or maybe 19VDC) that most of the things that currently have "bricks" need.
And if your house gets lower voltage DC, you're gonna have the problem of worth-stealing sized wiring to run your stove, water heater, or car charger.
I reckon it'd be nice to have USB C PD ports everywhere I have a 220VAC power point, but 5 years ago that'd have been a USB type A port - and even now those'd be getting close to useless. We use a Type I (AS/NZS 2112) power point plug here - and that hasn't needed to change in probably a century. I doubt there's ever been a low voltage DC plug/socket standard that's lasted in use for anything like that long - probably the old "car cigarette lighter" 12DC thing? I'm glad I don't have a house full of those.
Something to consider, and something I got a vivid demonstration of while playing with solar panels, DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe.
My understanding is that DC breakers are somewhat prone to fires for this reason, too.
Heh - I vaporised a fairly large soldering iron tip (probably 4mm copper cylindrical bar?), when I fucked up soldering a connector to a big 7 cell ~6000mAHr LiPo battery and shorted the terminals. Quite how I didn't end up blind or in hospital I don't know. It reinforced just how much respect you need to pay to even low-ish voltage DC when the available current was likely able to exceed 700A by a fair margin momentarily. I think those cells were rated at 60C continuous and 120C for 5 seconds.
heh man, I'm glad you got out of that easy, I definitely wore safety glasses 100% of the time after my experience. I think a lifetime of experience with dangerous wall outlets and harmless little 1.5V/9V DC cells teaches us the wrong lessons about DC safety. I've since heard stories of wrenches exploding when they fall across EV high voltage battery terminals. Wrenches aren't supposed to be explosive.
The electricians I was working with also told me stories about how with the really big breakers, you don't stand in front of it when you throw it, because sometimes it can turn into a cloud of molten metal vapor. And that's just using them as intended.
A bunch of those big breakers require two people. One person in a flash suit and another with a 2m long pole around the first person. That way if an arc flash happens, the second person can yank the first person to safety without also getting hurt.
Ruins the fun and interrupts instilling respect deep into the bones of interns.
Allegedly
While on "work experience" from high school I was put on washing power lines coming straight out of the local power station near the ocean - lots of salt buildups to clear.
Same deal, flashover suits and occasional arcs .. and much laughter from the ground operators who drifted the work bucket close.
This reminds me of the sailor who [decided](https://darwinawards.com/darwin/darwin1999-50.html) to measure his internal resistance by pushing probes through the skin on his thumbs and electrocuted himself with the 9V multimeter battery.
Mythbusters time. Salty fluids can be remarkably conductive. Blood qualifies. What's interesting though is that you have to wonder if there isn't some contributing factor here, as a kid I did this quite a few times, so that's one more for that list of stuff that could have killed me. At the same time: I didn't have nice insulation piercing tips back then (I do now) and that may be what saved me. I will definitely not try this again.
Another story in the same line is that I heard that a horse got killed by contact with a lantern battery, but I don't have any reference for that, just a story by a family member that collected coaches.
I have a couple of those narrow escapes one of which led me to put a significant chunk of Eastern Amsterdam out of power. Another involved Beryllium oxide. 9 lives are barely enough.
Ah! Perhaps you are a member of the gigawatt club? Eligible for entry once you have accidentally tripped off 1000 MW of load or generation! No sweeping that under the table
You brought back a memory, a second hand one, but still a great story. A guy I knew long ago had emigrated from NZ to NL. His main claim to fame in NZ was that one day he showed up drunk for work. In itself this wouldn't have been memorable, if it wasn't for his job, which was to manage a relatively small hydro plant on one of three shifts. On that particular day the plant had to be brought back online after being out for service and since it was really old the synchronization was manual. You had to control the flow of the water, monitor two concentric spinning wheels with the one driven by the grid and the other driven by the local genny and when the phase markings were lined up 'just so' you had to engage this frankenstein level switch to couple the grid to the generator and from there on inertia did it's thing so you could open up the gate to allow more water so the generator would start leading the grid effectively generating power.
Any kid could do it. Probably. But not a drunk one and instead of waiting long enough for both wheels to stay synchronized indicating there would be only a small jump in phase he just said f* it and connected the two anyway. Predictably, this led to a serious disturbance to the grid which in turn caused a whole lot of other stuff to disengage. Since his chances for re-employment on account of his new-found fame were somewhat minimal he decided to emigrate instead :)
I'm the idiot that sent a fairly high voltage spike into the grid setting off a cascade. Even years later I do not fully understand how it could happen, you'd think the grid would be low impedance enough to absorb a spike like that. But it set off a cascade on a part of the local grid that was known to be weak.
> DC arcs aren't self-extinguishing, unlike AC arcs. At one point I stuck a voltage probe in, and the arc stuck with it as I pulled the probe away. It also vaporized the metal tip of the probe.
It would have self-extinguished if you waited long enough for the probe to vaporize.
> My understanding is that DC breakers are somewhat prone to fires for this reason, too.
I think its that DC breakers are more expensive, so people use AC rated breakers instead. They are both rated for 400v @10 amps, its the same thing right?
It turns out they are not, and most people, even electronics types rarely play with 200v+ of DC.
I've had discussed with people familiar with the matter, and they convinced me its really not worth it for many reasons, the main one being safety - DC arcs are self sustaining - AC voltage constantly goes to zero, so if an arc were to form, it gets auto extinguished when the voltage drops. With DC this never happens, meaing every switch or plug socket can create this nice long arcs and is a potential fire hazard.
The 'what is safer' question for DC and AC at the same effective current and power has a mixed set of answers depending on conditions. For instance, DC is more likely to cause your muscles to contact and not let go (bad), but AC is more likely to send your heart into ventricular fibrillation (sp?, also bad).
AC arcs are easier to extinguish than DC arcs, but DC will creep much easier than AC and so on.
From a personal point of view: I've worked enough with both up to about 1KV at appreciable power levels and much higher than that at reduced power. Up to 50V or so I'd rather work with DC than AC but they're not much different. Up to 400V or so above that I'd much rather have AC and above 400V the answer is 'neither' because you're in some kind of gray zone where creep is still low so you won't know something is amiss until it is too late. And above 1KV in normal settings (say, picture tubes in old small b&w tvs and higher up when they're color and larger) and it will throw you right across the room but you'll likely live because the currents are low.
HF HV... now that's a different matter and I'm very respectful of anything in that domain, and still have a burn from a Tronser trimmer more than 45 years after it happened. Note to self: keep eye on SWR meter/Spectrum analyzer and finger position while trimming large end stages.
Thanks Jacques. So creepage is when current flows/arcs across the surface of an insulator, vs through the air. And it's worse with DC due to its unidirectional nature. Worsens when pollution builds up, or the surface degrades.
Indeed. And it's a really nasty thing to properly protect against because that pollution, especially with stuff that is unattended for a long time has a habit of ending up much worse than your worst fantasies. I've taken more than one electrocuted mouse out of the HV section of older color TVs for instance. Up to 250V or so it is manageable, above that you can get the weirdest problems including completely invisible arcing where the only giveaway is the ozone smell and the occasional click. Looking at HV circuitry in the dark or by putting a flame near a suspect spot is a great way to spot these kind of issues.
Really depends on what we're talking about. A lot of electrical safety equipment has a DC rating, usually something like 90VDC/300VAC. Also, most DC equipment just isn't going to have the stored energy to generate a big arc. Well, except batteries, and we're already piling them all around us.
I mean it depends, but for dual rated stuff has both a voltage and current limit, both of which are way lower.
Like typically a 230V/20A AC switch can switch 24VDC/2A. And the energy is not in the equipment, its in the mains (or batteries like you said, or PV panels)
Right, but that's why I mentioned safety equipment. Your common DIN-mount UL-489 branch circuit breaker will be rated for the same trip current, same short circuit current rating (SCCR), but lower voltage. So you can use the same wiring and breakers as you might have with AC and your 48V battery bank won't vaporize the $5 hardware store toggle switch that somehow became a shunt.
I mean, most AC circuit breakers use electromagnets to trip on overcurrent (as well as bimetallic strips using thermal methods for sustained high current).
Electromagnets dont work for DC, so your breaker will never trip. For thermal protection, you need current, so that checks out, and it would make sense for it to be rated under 50V as thats considered the highest voltage thats not life threatening on touch.
PV Batteries in general have a very high current (100s of A) at ~50Vish volts, so I dont think there's a major usecase for using household breakers for them.
Im still not getting your point BTW, switches and breakers are two separate things, with different workings, and household (and datacenter) DC would be I think around 400ish V, which is a bit higher than the peak voltage of AC, but still within the arc limits of household wiring (at least in 230V countries).
The advantage of DC is that you use your wiring more efficiently as the mean and peak wattage is the same at all times. Going with 48V would mean high resistive losses.
> Electromagnets dont work for DC, so your breaker will never trip.
If electromagnets don't work for DC then what am I supposed to do with this pile of DC solenoids and relays? ;)
> PV Batteries in general have a very high current (100s of A) at ~50Vish volts, so I dont think there's a major usecase for using household breakers for them.
That's what the SCCR rating is for. When there's a fault you're going to have a LOT of current flowing until your safety kicks in. Something like the grid or a battery bank will happily provide thousands of amps almost instantaneously. Breakers designed for protecting building wiring are rated for this. Now, most household breakers aren't dual DC/AC rated, but you can actually buy DC rated breakers that fit in a home panel (Square D QO series).
> Im still not getting your point BTW, switches and breakers are two separate things, with different workings, and household (and datacenter) DC would be I think around 400ish V, which is a bit higher than the peak voltage of AC, but still within the arc limits of household wiring (at least in 230V countries).
My point is that there isn't any material reason why DC can't be as safe as AC, all the proper safety equipment already exists. Extinguishing a DC arc during a fault is a solved problem for equipment at household scale.
> The advantage of DC is that you use your wiring more efficiently as the mean and peak wattage is the same at all times. Going with 48V would mean high resistive losses.
I just mentioned 48V because it's a common equipment voltage for household DC systems. 400V would be good for big motors and resistive heating loads.
Regarding DC vs AC and wiring efficiency, talking about mean vs peak wattage just confuses the issue. 1 volt DC is 1 volt RMS. It is an apples-to-apples comparison. If you want to say "we can use 170VDC or 120VAC with the same insulation withstand rating, and at lower current for the same power", then that is absolutely true. But your common 600V THHN building wire won't care if you're using 400V AC or DC, so it's mostly immaterial.
I've worked overseas a lot and one thing that's really different from 2 decades ago is that I simply don't need a step-down transformer anymore because every single thing I plug in converts to DC (or otherwise accepts dual-voltage) anyways. So I have a giant collection of physical plug adapters because every device I use just needs to fit into the socket and takes care of it from there.
I spent a few years getting flown out around the world to service gear at different datacenters. I learned to pack an IEC 60320 C14 to NEMA 5-15R adapter cable and a dumb, un-protected* NEMA 5-15R power strip. While on-site at the datacenters, an empty PDU receptacle was often easy to find. At hotels, I'd bring home a native cable borrowed from or given to me by the native datacenter staff or I'd ask the hotel front desk to borrow a "computer power cable," (more often, I'd just show them a photo) and they generally were able to lend me one. It worked great. I never found a power supply that wasn't content with 208 or 240V.
*: Some fancier power strips with surge suppression have a MOV over-voltage varistor that may burn up if given 200V+, rendering the power strip useless. Hence, unprotected strips are necessary.
That’s actually a recent phenomenon. Before the age of electronics most household appliances either worked with AC or DC equally well (like incandescent bulbs) or worked well with AC only given the technology at the time (think anything with a motor, fans, HVAC compressors etc).
Taking it to an extreme, the house I lived in while in grad school had wall lamp fixtures that doubled as electric and gas lamps. At some point I imagine it would have been possible to choose between using electric or gas by either flipping the switch or turning a valve. They said "Edison Patent" on them. We could have lit the house on AC, DC, or gas.
Thinking about the failure modes gave me the heebie jeebies, but the gas had been disconnected ages prior.
I lived in a 19th century house in San Francisco that had gorgeous plaster work medallions on the ceilings - think cherubs and fruits - in the middle of which were the light fixtures. One day my dumb-ass flatmate made an ill-advised attempt to DIY his light fixture and cracked the still-active gas line embedded in the ceiling. Sometime in the 1920s - the date was printed on a sticker in the electrical panel - when they electrified the house, they'd wrapped the electrical wires around the gas pipes, and left them otherwise in situ. Crazy stuff.
It’s kind of fun that light switches predate electricity. I think you used to turn a key, I guess you were turning a valve? Now that I think of it using a key to operate a valve makes a lot of sense but you don’t see it too often, well, I guess you want to turn things off without needing to find a key…
I'm renovating a house, and have been considering 24V or 48V DC outlets in a few rooms. Semiconductors become more expensive above ~32V, so 24V might be the sweetspot.
However, there's also PoE (24 or 48V!), so maybe that's the right approach. It's not like each outlet is going to run a heater anyway.
Lower voltage makes voltage drop across the line proportionally worse. Depending on the purpose PoE is probably the way to go since the wiring and hardware is all standardized and safety certified.
Unless you mean running AC and installing inverters in the wall? What is this even for? All my electronics are DC but critically they all require different voltages. The only thing I might benefit from would be higher voltage service because there are times that 15 A at 120 V doesn't cut it.
No, I meant running separate DC wires. I'm Europe, so it's 240 VAC vs 24/48 VDC. For small devices, 24 V would be useful in that you don't require an isolated SMPS, so cheaper endpoints are possible. Slightly less risk of burning down the house with some cheap Chinese AC/DC. 24 V is still high enough to use USB PD/PPS at 20 V, and I doubt I'll run enough current that the losses due to lower voltage would be a problem.
For PoE, I thought it was standardized at 48 V, but I see lots of cameras run at 24 V, and I think I've even seen 12 V. Seems a bit of a mess.
Need expensive printers and you need CAD software that can correctly move the teeth. Also not all it can be done by software, sometimes you need to blank out certain teeth that dentist will make the call.
Not even the most dangerous job in the US. Forest workers, commercial fishermen, pilots etc are more dangerous. If we're talking about gun violence, your corner market cashier is more likely to get shot, Has anyone thanked a 7 eleven worker for their sacrifice thas you can get a slurpee at 2am?
I don't think you can use this datapoint for this purpose. Cops are employing the paranoid strategies already, so there's no way to discern between 'these strategies are needless' and 'these strategies are effective'.
You could probably do a comparison between jurisdictions where police homicides are common and jurisdictions where they aren't common. Assuming that there are cultural factors anyway.
Like sure, areas with higher rates of criminal violence will probably have more police homicides, but it's likely enough that you can pair things up based on rates of criminal violence.
Curious how much this varies among police. Some jobs are by their nature always dangerous.
But there are a lot of cops in the USA, and plenty I'm sure have nice, cozy jobs, and then there are some who spend thee majority of their career policing areas that more closely resemble warzones or 3rd world nations but this isn't the majority by any means.
Depends on how you look at the numbers. But construction, logging, garbage collection and truck driving tend to be the most deadly depending on the specific metric (absolute, per capita, by industry, etc).
Expanding that, the deadliest part of being a police officer is almost certainly the driving component. No gun will save you from smashing your SUV into a pole. And the aftermarket modifications made to the vehicles aren't crash tested. A police cruiser is full of potential projectiles.
It's a chance for $400m. Doesn't mean he can get the $400m, since legally it still isnt his and it still can get seized after he gets out if he ever tries to cash it in,
Pen input is the one factor that forced one of my kids to a Windows laptop for school (a Surface Pro). It was a required feature for his school. Seeing how much he uses it for note taking, I get it. So yes, drawing is a key feature for schools.
Another school uses iPads with keyboards for the same purpose, so I'm not sure where the school market is for these. Maybe only older kids, but a lot of edu-tech is expecting some kind of touch/pen input.
It might be a fine laptop when you are on the move. I have an educational Lenovo for that purpose, but I would appreciate a Mac for that same use. When I need more power away from my desk I can use the MacBook Pro or my Lenovo T series (both a lot heavier than I’d like).
I just wish the Mac had 16GB of RAM but my tiny Lenovo has 8 and it’s been working OK so far - I haven’t even set up a proper swap partition and it’s running on zram.
But Anthropic can't be a winning bidder, can they? They're specifically saying they won't offer certain services that the US Gov wants. Therefore they de facto fail any bid that requires them to offer those services. (And from Anthropic's side, it sounds like they're also refusing to bid for those contracts.)
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