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| Single Pole or 1P + N circuit breakers |
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| Monkeh:
--- Quote from: bsdphk on March 30, 2019, 08:11:17 pm ---This is one of the most damaging kind of discussions we have here on EEVblog. Far too many people seem to assume that in the rest of the world electricity is just like where they live themselves. --- End quote --- The basic principles are no different and in most cases (Norway sounds interesting. You might look up our term, 'equipotential zone'.) the protective systems are broadly equivalent. But I guess discussing and learning is just too damaging. Especially when I started discussing with a member from my own country, I mean, I really could be mixing things up there.. |
| Zero999:
--- Quote from: Monkeh on March 30, 2019, 08:05:02 pm --- --- Quote from: Zero999 on March 30, 2019, 07:55:07 pm ---I don't see how disconnecting the neutral, as well as the phase is any more dangerous, than just disconnecting the phase. There can be an argument made for the case that it's not necessary to disconnect both conductors, in most applications, but it's completely wrong to imply it's more dangerous. --- End quote --- When have I implied it's more dangerous? --- Quote ---The fact is, it's clearly safer to disconnect both conductors, this isolating the entire system, whether or not it's absolutely necessary or not. --- End quote --- I see no valuable safety benefit to enforcing isolation in an overcurrent device. Only greater expense and an additional point of failure, and yes, MCBs fail. Of course, if you happen to be dealing with a multiple-line scenario with no neutral, the isolation comes for free - but they're still not made for repeated manual operation, and can fail to close again. --- Quote ---Any thread involving safety inevitably turns into a shitfest. One should state, their reasoning for why x is safer then y, cite the relevant regulations, then move on and ignore all the dangerous misinformation which follows: hopefully anyone with any common sense will be able to pick through it all. :horse: --- End quote --- Regulations are behind a paywall, and I am not an electrician. I note you haven't been citing any, either. My reasoning that it is not necessarily and beneficially safer is that there is no guarantee (in the vast majority of scenarios, not even a possibility) of a device triggered only by the line being able to clear any fault scenario involving the neutral. I am very open to reasoned fault scenarios I've missed. I have been attempting to tease them out for a while now. --- End quote --- I apologise, I didn't post any standards. I thought Soldar did, but I was mistaken. To clear up the confusion. In many cases a circuit breaker needs to perform both isolation, as well as overcurrent protection, hence the requirement for double pole breakers by some electrical standards. Granted this isn't always necessary, but sometimes it is. If it wasn't, then double pole breakers wouldn't exist. |
| bsdphk:
If by "broadly equivalent" you mean "tries to avoid fire and death" then you are entirely correct. And you are of course welcome to discuss and learn about this topic, which is incredibly interesting to its core, I'm sure there are a lot of failure modes you have never considered. But giving advice on what type of protection device to employ, without knowing what the relevant electrical code contains, is just plain irresponsible. |
| Monkeh:
--- Quote from: Zero999 on March 30, 2019, 09:02:57 pm ---To clear up the confusion, in many cases a circuit breaker needs to perform both isolation, as well as overcurrent protection, hence the requirement for double pole breakers by some electrical standards. Granted this isn't always necessary, but sometimes it is. If it wasn't, then double pole breakers wouldn't exist. --- End quote --- In which circumstance is this necessary? Honest question. TT installations here use dual-pole time-delayed RCDs to cover the cases I'm familiar with - you can't even get 1P+N MCBs for many if not most domestic and small commercial boards in the UK. Let's also be specific with terminology: SP or 1P - single pole breaker, 1P+N - single pole breaker with switched neutral, 2P or double pole - dual pole breaker with overcurrent protection on both poles. 2P are used for split-phase or two phases from a three-phase supply. I recall seeing 2P+N and 3P+N as well in a catalogue somewhere. 1P+N breakers are, to my knowledge, primarily used to provide isolation for service without requiring the isolation of the entire installation or equipment. This is a valid use case! But it is an additional one on top of the primary (and in SP devices, sole) purpose of overcurrent protection, and is nothing more than operating it as a switch (re: this is not a functional switch..). Standard single pole MCBs are not isolators and are not to be used as such, and standard installation practices here, at least, do not call for 1P+N MCBs to provide that capability. If standards elsewhere do, that's potentially a nice bonus, subject to my concerns about resettability (I have seen otherwise good MCBs simply fail to reclose as the mechanism is not designed for operation as an isolator, and is only required to remain capable of opening, not closing). It's also a large waste of space in almost all normal conditions, as most 1P+N breakers used seem to be two units wide, and in domestic situations isolating the entire installation isn't usually a problem. --- Quote from: bsdphk on March 30, 2019, 09:09:31 pm ---If by "broadly equivalent" you mean "tries to avoid fire and death" then you are entirely correct. And you are of course welcome to discuss and learn about this topic, which is incredibly interesting to its core, I'm sure there are a lot of failure modes you have never considered. But giving advice on what type of protection device to employ, without knowing what the relevant electrical code contains, is just plain irresponsible. --- End quote --- They generally try to avoid fire and death in almost exactly the same way, with few significant variations. American variations are quite interesting (everything is de-rated after the fact, a 20A circuit may not carry 20A, etc), and to my knowledge their degree of testing is limited in the extreme. It's a little disturbing. I have been asking for conditions I have not considered. Repeatedly. As for giving advice - I haven't! Others already said follow the local code and I considered that quite adequate advice, although I might also say "hire an electrician if you can't answer your own question". That advice often gets me shouted down, however. |
| bsdphk:
"hire an electrician if you can't answer your own question". That advice often gets me shouted down, however." Not only if you can't answer your own question, but also because it is the law in all of EU as far as I know. The derating in USA codes is very much because people are allowed to bodge their own installation and they are not very good at it |
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