Yes they are. Current alternates direction, but power usually only flows in one direction, from the input terminal (from the bus bar) to the output terminal (that the circuit is wired into).
If the circuit will be supplying power too (e.g. battery storage, an EV and EVSE that supports powering the house from the EV, etc) then you need a bidirectional RCBO.
People with no differential fault protection need not worry about any of this, they'll just be killed when it goes badly wrong.
EDIT: To say nothing of people with unidirectional electricity meters; plugging these into those setups will get them prosecuted for electricity theft. All SMETS 2 smart meters are bidirectional; you'd best check your meter if it isn't one of those.
Between the phasing out of analog meters (the latter half of the last century) and the introduction of smart meters (2010), a lot of electronic prepayment meters produced for the UK market would set a tamper flag if they detected power flowing backwards through them, as a proxy indication of an attempt at electricity theft. These meters will refuse top-ups in this condition, requiring you to contact your energy supplier to sort it out, leaving you without power until you do and then exposing you to scrutiny when they arrive.
Pre-smart non-prepayment electronic meters (for those with old meters, still submitting manual readings, and paying by direct debit) will be fine. Most of these meters, and all smart meters, are inherently bidirectional, because they maintain 4 counts (energy imported and energy exported, in kWh and kVARh) and your energy provider will do all the necessary math to figure out what to actually bill you for (residential customers are not billed for kVARh usage).
The UK government in 2011 announced plans to have 50 million smart meters installed by the end of 2020. In typical overpromise underdeliver government fashion, they didn't even achieve half of that; by then, only 23.6 million had been installed, and of those, 4.5 million had stopped working because they were initially (and stupidly) designed to be tied to a specific energy provider and the customer had changed provider. This even affected me.
Nevertheless they'd still accurately track energy consumption and export even if they'd lost their reporting capability, so you have nothing to fear here. This situation has been rectified at the redesign stage with provider-independent SMETS 2 meters, and all SMETS 1 meters still in service have been hotpatched to bring them into line (restoring their smart functionality regardless of provider).
Even today (well, as of last September), this number is only 40 million, with only 36.7 million of them actually working as designed (reporting readings automatically).
This leaves up to 16 million properties with a meter that may stop working and expose you to a theft investigation when you obtain generation capacity that even momentarily exceeds your usage (for example if you have a dual RCD board and one of the RCDs trips, taking out half of the circuits in your home, but not the one the inverter is plugged into).
Realistically the true figure is probably around a quarter of that; prepayment meters were very popular among the renting population of the time, and those who wanted to track their energy usage carefully and only pay for it with cash as and when needed, and sometimes people had these meters forced upon them by suppliers after the customer had demonstrated poor payment history, but they were far from the norm.
Average home owner buying plug-in solar at a supermarket isn't going to know or care about any of this. They'll just plug it in, and it will work, until one day maybe it doesn't and their supplier opens a theft investigation.
I feel like the meter suddenly "breaking" is the substantially larger inconvenience. Presumably the supplier will raise an eyebrow at the flag, glance over the place, see the solar setup and get on with life. At least one would hope. They must have seen this a time or two by now after all.
The kind of meters we used to install 50 years ago would turn backwards if electricity flowed backwards.
So if you spent a week with the meter connected normally, then you swapped the input and output cables around for a week, the meter would be back at zero. Free electricity!
They used anti-tamper seals to make it more detectable, but there are ways around that sort of thing.
That’s an RCD, not a breaker. Guess the English still insist on using nonstandard terminology, like “lift”, “bonnet”, “torch”, and, apparently, “breaker”. Oh well.
This is not an RCD, it's an RCBO. It combines the functions of an MCB (Miniature Circuit Breaker) and an RCD (Residual Current Device) in one device, as specified by BS EN 61009 (Residual Current Operated Circuit Breakers with Integral Overcurrent Protection).
It would be really interesting to know what's so special about these UK units that they can be "damaged" by being fed from the "wrong" side (as per some other article), considering that the only place where these behave like that is an island north of France.
These are not just circuit breakers/MCBs, they are RCBOs which combine an MCB + RCD in a single unit. RCDs traditionally only measure - and protect - current flow is one direction, so if you are using them for solar you need a bi-directional unit for full protection. The device will not be damaged, it just won't protect you.
However in the case of a UK home, where you may have a single ring circuit connecting all the sockets on the whole floor, what's in the breaker panel isn't going to protect you with plug-in solar anyway. Better hope what you are plugging in meets UK standards and isn't just some Chinese rubbish that claims it does.
Outside the UK, neither RCDs nor RCBOs (type A/AC) are generally distinguished by bidirectionality (all search results about this being .co.uk), since the RCD part of these devices is just a current transformer driving a trip solenoid; there is nothing in it that's powered by the line, nor something which could sense net power flow direction. The situation is different for AFDDs or type B RCDs, since those have active, powered electronics in them which need to be fed from the line side.
After some research the main reason seems to be two-fold:
Answer #1: Many UK RCDs/RCBOs are actually single-pole devices and don't disconnect the neutral. In the simplest case, this means pressing the test button might burn out the test resistor when backfed. I don't imagine this to be a problem in practice, since grid-tie inverters shut down very quickly if the grid disappears under them, especially plug-in inverters. RCDs/RCBOs elsewhere are virtually always disconnecting the neutral, so don't care about this.
Answer #2: It looks like some/many one-module wide UK RCBOs _do have_ electronics in them, even if type A, because they're actively driving the trip solenoid of the MCB part, and if you sketch this out and do it in a very cheap way it's easy to see how you could burn that out if backfed (i.e. powering the trip solenoid during a fault is assumed to disconnect in a very short amount of time, but if backfed for longer than the disconnect time that might be enough to toast the solenoid or the driver).
Notably neither of these has anything to do with the direction of power flow.
> Answer #1: Many UK RCDs/RCBOs are actually single-pole devices and don't disconnect the neutral.
This is not correct; all type AC and type A RCDs used in British consumer units disconnect the neutral as well. Some RCBOs do not disconnect the neutral and this is a problem in some circumstances. The datasheet I linked for Wylex NHXS1 RCBOs explains that these ones do disconnect the neutral.
> Answer #2: It looks like some/many one-module wide UK RCBOs _do have_ electronics in them [...] but if backfed for longer than the disconnect time that might be enough to toast the solenoid or the driver
This is correct. For an example of this construction in an RCBO, see [1]. This illustrates that if the supply is connected to the "To Load" part of the schematic (toward the end of the video), as it would be if the supply is a solar PV inverter with battery storage, then it can continue powering the electronics and be shunted out by the thyristor after it has supposed to have tripped, very quickly burning itself out.
Bidirectional RCBOs are not designed in this manner. They have more complicated circuitry that makes them more expensive to manufacture, but are absolutely required in situations like this if you don't want your protective devices to burn and/or explode when they operate.
> Notably neither of these has anything to do with the direction of power flow.
Yes it does, because if the power is flowing backwards to how they designed it, that is backfeeding it, keeping its circuitry powered after it should have been disconnected.
NEC doesn't specify GFCI breakers, it merely requires receptacles in certain areas have GFCI protection, and accepts GFCI breakers as one way to provide that.
The conventional practice in the US is still to use GFCI receptacles rather than breakers.
Because NEC 210.12 requires all devices to be protected. Which means if you have a switch or splice before a plug the only way to protect those is with an AFCI breaker. The only exception is a continuous run from the breaker to an outlet in metal conduit or MC cable. Given how much is romex this effectively forces AFCI branch breakers.
I find that receptacles tend to break prematurely if they are wet locations, even if 'protected' with a weatherproof box etc. You also need to know where the receptacle is and make sure it is accessible instead of behind a piece of furniture etc. Then some electricians misunderstand and put receptacles throughout the run (much more expensive than one breaker which is about 2x a receptacle), and in edge cases you need to know the order in which to reset them to get things working again. I much prefer to just have everything in the panel.
Always important to note that "code" does not mean "must meet this standard". Many existing installations will not meet current code and there are varying levels of code (at least in the UK) that mean anything from an electrician can ignore minor faults through to network-notifiable issues.
But that's rather the point here that consumers are the ones who are going to be plugging in these devices, with no appreciation for their circuits and safety devices. The only code that matters is the last version of it adhered to when their home was last wired. In extremes, that can be 40 years or more.
sure, but everything new must meet current code. nobody upgrads when code changes anywhere. Codes from 40 years ago were not bad, though things are always improving.
> And as for extensions - gone are the days of PCIe. Audio cards and other specialized equipment works and lives just fine on USB-C and Thunderbolt.
Grumble grumble. Well, there used to more than audio cards, back before the first time Apple canceled the Mac Pro and released the 2013 Studio^H^H Trash Can^H^H Mac Pro.
Then everyone stopped writing Mac drivers because why bother. So when they brought the PCIe Pro back in 2019, there wasn't much to put in it besides a few Radeon cards that Apple commissioned.
The nice thing about PCIe is the low latency, so you can build all sorts of fun data acquisition and real time control applications. It's also much cheaper because you don't need multi-gigabit SERDES that can drive a 1m line. That's why LabVIEW (originally a Mac exclusive) and NI-DAQ no longer exist on Mac.
USB-C oscilloscopes work because the peripheral contains all the hardware, so it doesn't particularly matter that the device->host latency is high. They also don't require much bandwidth because triggering happens inside the peripheral, and only the triggered waveform record is sent a few dozen times per second.
> It's not the Mac's or Apple's fault. We are actually live in the age where systems are quite independent and do not require direct installations.
It is, and we don't. Maybe you don't notice it, but others do.
> USB-C oscilloscopes work because the peripheral contains all the hardware, so it doesn't particularly matter that the device->host latency is high.
Yeah, that's basically the way accessories have gone. Powerful mcu's and soc's have gotten cheap enough to make it viable. Makes me a little sad though, I liked having low latency "GPIO's" straight to software running on my PC (but I'm thinking as far back as the parallel port... love how simple that was).
It's not just that - anything working with analog signals benefits hugely from not living inside the complete EM interference nightmare of the computer case.
With USB4/TB you can get quite far in both latency and throughput. Actually there are network adapters with TB connection that are just TB to PCIe adapters and PCIe network card.
What's notable about the initial segment is that it parallels (and thus duplicates) an existing Amtrak service between Bakersfield and Merced. So the initial operating segment gives us zero new destinations by rail.
But, hey, you'll be able to go really fast between California's 6th and 80th largest cities!
Some of the aqueducts that deliver some of the water to LA do rely on pumping. But, the Los Angeles Aqueduct, which is the subject of this post, does not. The LA Aqueduct is entirely gravity driven, and under normal circumstances it is sufficient to supply LA's water needs.
Another nitpick is that California's various aqueducts are net producers of electricity (i.e., after accounting for pumping), so, while some of them do rely on electricity, they do not require an external source of power to operate.
> It's also why the SSD is slower than a MacBook Pro or MacBook Air;
It's actually not that much slower, at least if you compare machines with the same amount of storage. The M2 and M3 MacBook Air with 256GB comes in at 1700 MB/s[1], while the Neo with 256GB is... drumroll... 1700 MB/s[2].
Yes, Air and Pro machines with more storage are faster. I have not seen any benchmark of the Neo with 512GB, so maybe it lags behind the Air and Pro there. But I've not seen anyone publish a benchmark which actually demonstrates that.
I should clarify that I was referring to the memory bandwidth. Compared to the 100 GB/s of a M3 MacBook Air, the 60 GB/s of the Neo is 40% slower. My M1 Pro MacBook Pro's memory bandwidth is 200 GB/s; that's 3.33x faster than the Neo.
With respect, I think you're misremembering the product lineup in the 1994/5/6 era.
Back then, Apple had 16 to 32 distinct models[1] of just desktop computer (just the desktops!) with little to distinguish them. In many cases, the exact same internal hardware was shipped in two different boxes as two models aimed at two different customers (LC/Performa/Centris/Quadra/Workgroup Server). For example, the "LC 550" and "Performa 550" were the exact same computer[2] with two different names on the front, meant to be sold to the educational and home markets.
That's extremely confusing for the consumer. You had the same internal hardware being sold for two different price points, and computers with significantly different performance sold at the same price point. You don't want your customer to get analysis paralysis and give up before they purchase.
The point of Jobs's simplification is that there is one option for you to pick at a given price point in a given category of tablet/laptop/desktop, and that pricing and capability are clearly aligned. I don't see where Apple has gotten away from that.
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