7 ms·

“Unidirectional breakers” aren’t a thing for AC circuits.

jonatron 6mo ago
https://www.bgelectrical.uk/uk/circuit-protection/devices/rcbo https://www.bgelectrical.uk/uk/circuit-protection/devices/rc... Right there, both bidirectional and unidirectional breakers.
- formerly_proven 6mo ago
  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.
  - fy20 6mo ago
    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.
    - formerly_proven 6mo ago
      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.
      - aaronmdjones 6mo ago
        > 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. [1] https://www.youtube.com/watch?v=8kWIITspYvk https://www.youtube.com/watch?v=8kWIITspYvk
hamdingers 6mo ago
Not in the US, but in parts of Europe they effectively use AFCI/GFCI breakers for everything.
- bluGill 6mo ago
  Those are code in the us now too. (with exceptions for where they don't make sense)
  - oliwarner 6mo ago
    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.
    - bluGill 6mo ago
      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.
  - hamdingers 6mo ago
    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.
    - bluGill 6mo ago
      Right, but the NEC spec arc fault as well (i've only seen this on breakers). recepticals are cheaper and otherwise just as good.
aaronmdjones 6mo ago
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. Source: Am a UK electrician Example: https://assets.cef.co.uk/downloads/pdg/wylex_nhxs1b32_datasheet/wylex_nhxs1b32_datasheet.pdf https://assets.cef.co.uk/downloads/pdg/wylex_nhxs1b32_datash... 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.
- fc417fc802 6mo ago
  I don't follow you regarding unidirectional meters and electricity theft. How does that work?
  - aaronmdjones 6mo ago
    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.

https://www.bgelectrical.uk/uk/circuit-protection/devices/rcbo https://www.bgelectrical.uk/uk/circuit-protection/devices/rc... Right there, both bidirectional and unidirectional breakers.

formerly_proven 6mo ago
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.
- fy20 6mo ago
  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.
  - formerly_proven 6mo ago
    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.
    - aaronmdjones 6mo ago
      > 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. [1] https://www.youtube.com/watch?v=8kWIITspYvk https://www.youtube.com/watch?v=8kWIITspYvk

hamdingers 6mo ago

Not in the US, but in parts of Europe they effectively use AFCI/GFCI breakers for everything.

bluGill 6mo ago
Those are code in the us now too. (with exceptions for where they don't make sense)
- oliwarner 6mo ago
  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.
  - bluGill 6mo ago
    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.
- hamdingers 6mo ago
  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.
  - bluGill 6mo ago
    Right, but the NEC spec arc fault as well (i've only seen this on breakers). recepticals are cheaper and otherwise just as good.

aaronmdjones 6mo ago

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. Source: Am a UK electrician Example: https://assets.cef.co.uk/downloads/pdg/wylex_nhxs1b32_datasheet/wylex_nhxs1b32_datasheet.pdf https://assets.cef.co.uk/downloads/pdg/wylex_nhxs1b32_datash... 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.

fc417fc802 6mo ago
I don't follow you regarding unidirectional meters and electricity theft. How does that work?
- aaronmdjones 6mo ago
  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.