Single Pole or 1P + N circuit breakers - Page 1
Forum section: electronics / beginners

author: made2hack
author_rank: Frequent Contributor
timestamp: March 26, 2019, 01:28:22 pm
content: Hi all,I'm currently installing a new electrical panel in my workshop and would like to know whether to use just 1P (1 pole or Live only) circuit breakers? Or 1P + N (Live + Neutral) circuit breakers?This is for EU, 220-240VAC single phase.I keep finding conflicting information as most search results seem to come up as 2 Pole variants (used in North America).Are 1P + N "safer" if you will than just 1P that disconnects just the live? Any advantages?Thanks,P.S: The panel will also have a 1P+N 30mA differential before the individual circuits.

author: Zero999
author_rank: Super Contributor
timestamp: March 26, 2019, 01:58:26 pm
content: Disconnecting the neutral is safer, because it might be live, if it's broken somewhere upstream of the breaker.

author: made2hack
author_rank: Frequent Contributor
timestamp: March 26, 2019, 02:43:14 pm
content: So it's just for upstream concerns? But would you also wire a house using the same consideration?

author: made2hack
author_rank: Frequent Contributor
timestamp: March 26, 2019, 04:01:22 pm
content: Of course I am assuming that this type 1P + N blows at the same time, I mean the breaker breaks both connections and is not like a 2P where one pole might still be active.

author: Zero999
author_rank: Super Contributor
timestamp: March 26, 2019, 04:08:52 pm
content: Quote from: made2hack on March 26, 2019, 04:01:22 pmA two pole breaker always blows both at the same time.Whether it's necessary or not depends on how it's wired and your local regulations. In the UK, the neutral and earth is normally combined in the same conductor up to where it enters most houses, so a single pole breaker is sufficient. I can't comment about other places.

author: capt bullshot
author_rank: Super Contributor
timestamp: March 26, 2019, 04:16:04 pm
content: Depends on your local regulations. Do it the same way your main breaker panel is made.E.g. in Germany, 1P+N breakers are totally unknown and not used but I've seen such things in other European countries. Otherwise for a Ground Fault Interrupter, it's normal to break all phases and Neutral (1P+N or 3P+N).In general I do consider disconnecting the Neutral rather dangerous, since a broken Neutral can cause strange and/or dangerous things to happen. So as you said, ensure the breaker breaks all phases together.

author: Benta
author_rank: Super Contributor
timestamp: March 26, 2019, 05:05:05 pm
content: ^^^ This.

author: ejeffrey
author_rank: Super Contributor
timestamp: March 26, 2019, 05:07:49 pm
content: Certainly in north america standard circuit breakers only interrupt the live conductor. Neutral is bonded to ground in the panel, so there is no need or desire to break it.NA has two-pole 240 V breakers because we use split phase systems where both legs are live. In a 120/240 4 wire circuit the breaker would interrupt the two live wires but not neutral or (of course) ground. Similarly for a three phase circuit you would break all three live wires but not normally neutral.However: there are differences from country to country about where and how the safety earth is connected to neutral so it is important to check your local regulations and wiring standards.

author: Zero999
author_rank: Super Contributor
timestamp: March 26, 2019, 08:14:30 pm
content: Quote from: ejeffrey on March 26, 2019, 05:07:49 pmYes, that's mostly the case here too. I say mostly, because I can think of instances where that may not be the case. For example, if there's an outbuilding with a thick cable running to it from the main property, it will have its own distribution panel and will not bond the neutral to earth again there. In that case, to mitigate the danger posed by a poor neutral connection, which would make the neutral float at a dangerous voltage, the breaker should disconnect both the neutral and phase conductors.

author: made2hack
author_rank: Frequent Contributor
timestamp: March 26, 2019, 09:02:05 pm
content: Quote from: Zero999 on March 26, 2019, 08:14:30 pmIs there any reason why I wouldn't be able to bond the neutral and earth in this sub panel?

author: notsob
author_rank: Frequent Contributor
timestamp: March 26, 2019, 09:15:34 pm
content: We had a case where a repair technician was hung up [ie. live power on his arm] on a card reader [ the size of 2 washing machines], an operator nearby had to run and drop the main breaker for the building. the breaker on the card reader was phase only - not neutral. However the person that wired the plug under the false floor had wired it incorrectly. So the card reader breaker was actually switching neutral. Very close call, we almost lost that person.So be safe - switch both.

author: Monkeh
author_rank: Super Contributor
timestamp: March 26, 2019, 09:38:27 pm
content: Quote from: Zero999 on March 26, 2019, 01:58:26 pmThis is irrelevant for the purpose of a circuit breaker. It is not isolation, nor is it functional switching - it is overcurrent protection.

author: Zero999
author_rank: Super Contributor
timestamp: March 26, 2019, 10:59:53 pm
content: Quote from: Monkeh on March 26, 2019, 09:38:27 pmNo it's not irrelevant. It still has to make the circuit safe, i.e. dead, which won't happen with a single pole device, if there's a break in the neutral conductor.

author: Monkeh
author_rank: Super Contributor
timestamp: March 26, 2019, 11:11:34 pm
content: Quote from: Zero999 on March 26, 2019, 10:59:53 pmIt has to end the condition of overcurrent. Again, it is an overcurrent protective device,not an isolator.

author: ejeffrey
author_rank: Super Contributor
timestamp: March 27, 2019, 04:05:36 am
content: Quote from: notsob on March 26, 2019, 09:15:34 pmNo. If you are talking about building wiring (i.e., distribution panels), rather than equipment wiring, do it the way your local code and standards specify. Do not install some unapproved non-standard device because some guy on the internet said so.Edit: For instance, in the US it is allowed to have two branch circuits that are fed from opposite phases of the split phase input share a common neutral as long as the wires are run together (same Romex or same conduit). In industrial/commercial settings it is allowed have three branch circuits on three phases share a neutral. These do not use multi-pole circuit breakers but have independent circuit breakers for each branch circuit. If someone listened to this "advice" and went and replaced one of the branch circuits with a breaker that switched both live and neutral, then you would have created a potentially dangerous situation where the other circuit(s) could have live but a broken neutral. In the three phase case, the two remaining phases will try to force current balance causing one circuit to take a potentially severe overvoltage.Even if you think this practice is dumb and that those circuits should be on a single multi-pole breaker, that is not the way it is done or the way anyone would expect it, and unilaterally changing part of the system because of your opinion can cause hazardous conditions. Don't do it.

author: Zero999
author_rank: Super Contributor
timestamp: March 27, 2019, 01:25:57 pm
content: Quote from: Monkeh on March 26, 2019, 11:11:34 pmIt still has to make the circuit safe, i.e. isolate it. Over-current can cause electric shock, as the voltage on exposed metal parts can reach dangerous levels. Whether or not the circuit breaker is supposed to be used for isolation or not. It must safely disconnect the circuit from the supply.

author: soldar
author_rank: Super Contributor
timestamp: March 27, 2019, 07:30:28 pm
content: In Spain regulations require the circuit breaker to break both conductors and I understand there are several good reasons to do so but in my apartment I have a very simple panel which only cuts the phase side and not the neutral wire.Regulations here also require a GFCI which protects all circuits and cuts both wires but I have it protecting only kitchen and bathroom but not the other rooms.

author: Monkeh
author_rank: Super Contributor
timestamp: March 27, 2019, 07:49:59 pm
content: Quote from: Zero999 on March 27, 2019, 01:25:57 pmNo, it has toclear the fault. Isolation is not the same thing.

author: Benta
author_rank: Super Contributor
timestamp: March 27, 2019, 08:34:28 pm
content: Quote from: Monkeh on March 27, 2019, 07:49:59 pmAgreed.Let's go back some years: circuit breakers were thermofuses/filaments that melted. They were only placed in the live conductor in the fuse panel.The resettable breakers have the same function, which is to open the circuit in case of overload.Fusing neutral is nonsense.

author: soldar
author_rank: Super Contributor
timestamp: March 27, 2019, 09:06:30 pm
content: Quote from: Benta on March 27, 2019, 08:34:28 pmIn Spain it is required by the regulations and there are several good reasons. One is that some places are supplied 230 V with two phases from a 127/230 volt system and there you, obviously, need to cut both wires just like in America you need to cut both wires in a 220 V circuit.And there are other reasons.Also, there are different ways of implementing and connecting protective earth and a lot of people think there is only one correct way to do it and any other way is wrong.Again, in my apartment I have single circuit breakers on the phase side but there are good reasons to cut both wires after an overload or GFCI.In Spain, like most of central Europe, we use Schucko plugs which are an abomination to everything that is decent and holy. Non-polarized, requires great force to pull, earth tabs can bend out or shape or make bad contact, too big.

author: Monkeh
author_rank: Super Contributor
timestamp: March 27, 2019, 09:11:17 pm
content: Quote from: soldar on March 27, 2019, 09:06:30 pmThat's not fusing the neutral, becauseit isn't a neutral.

author: soldar
author_rank: Super Contributor
timestamp: March 27, 2019, 09:45:21 pm
content: In Spain the electric code requires cutting all conductors, always, including neutral, always. always.I thought I had made that clear in my earlier post.Relevant regulation isReglamento de Baja Tensión ITC-BT-17. It mandates (1) General shutoff switch which must cut all wires, (2) General GFCI which must protect all circuits and cut all wires, (3) individual circuit breakers which must cut all wires.

author: Monkeh
author_rank: Super Contributor
timestamp: March 27, 2019, 10:26:41 pm
content: Quote from: soldar on March 27, 2019, 09:45:21 pmI didn't claim otherwise. I simply made the point that if you have two active conductors you don't have a neutral.I've yet to see any of the good reasons for requiring a breaker to interrupt neutral.

author: soldar
author_rank: Super Contributor
timestamp: March 27, 2019, 11:09:57 pm
content: Two scenarios I can think of.(1) If the neutral wire breaks then the neutral wire can be brought to live voltage through devices plugged in.(2) If a 220/380 distribution transformer fails and temporary emergency supply needs to be provided it can be done with a 127/230 transformer or 127/230 mobile generator using two live phases.I am sure there are others.I am not saying it is a must do. Every technical decision has its pros and cons. Cutting both conductors is, obviously, safer. OTOH there is added cost and complexity.As I said, In my apartment I only cut the live wires because I like it that way but it does not meet code regulations.Note also that in Spain earth and neutral are not connected as they are in America. Another case of doing things differently.

author: Monkeh
author_rank: Super Contributor
timestamp: March 27, 2019, 11:22:48 pm
content: Quote from: soldar on March 27, 2019, 11:09:57 pmIf the neutral wire upstream breaks, how many additional faults are required for danger to be present?QuoteThat is a very country specific situation involving attempting to connect two incompatible systems, and requiring the use of a two-pole breaker universally is a lazy fix at best.QuoteIf earth and neutral are not connected then by definition there is no neutral. Note that I'm not American, also..

author: Brumby
author_rank: Unknown
timestamp: March 28, 2019, 12:40:10 am
content: Quote from: Monkeh on March 27, 2019, 11:22:48 pmIf earth and neutral are not connected then, by definition, there is no functional earth, either.I think the point being made is more:Quote from: soldar on March 27, 2019, 11:09:57 pm

author: Zero999
author_rank: Super Contributor
timestamp: March 28, 2019, 08:48:30 am
content: Quote from: Benta on March 27, 2019, 08:34:28 pmRead the thread again. No one is talking about fusing the neutral, which would be dangerous, because if the fuse breaks, the live would still be connected.We're talking about a double pole circuit breaker, which is a double pole single throw switch and disconnects both the live and neutral conductors. Soldar is right, disconnecting both conductors is safer, than only one, because an upstream fault could mean the neutral conductor is live.In situations where there's a risk the neutral might not be neutral, a double pole breaker must be used. If this wasn't a requirement, then they wouldn't exist!

author: soldar
author_rank: Super Contributor
timestamp: March 28, 2019, 09:02:30 am
content: In engineering many decisions have to weigh several considerations and there is no one absolutely correct answer. Different countries with different boards come to different rules and anyone can disagree with the rules. In many cases there are historical considerations.IMHO polarized plugs are very high up in my list of priorities and yet continental Europe is stuck with the abominable Schucko plug for historical reasons from Germany which today would be irrelevant if we were starting out from scratch.Historical reasons explain things which are difficult to explain otherwise. I understand in Japan they have a mish-mash of voltages and frequencies.In Spain the code mandates cutting off all poles and it certainly adds safety. The question is how much safety it adds and whether it is justified in terms of cost and complexity. I guess the answer might depend on whether the person who died of electrocution was your daughter or your mother-in-law.OTOH, the code in Spain allows flexible multi-strand cables in conduit for permanent wiring. I do not like that and I believe it adds risk but the panel who made the rules gave more weight to the fact that flexible cable is much easier to feed through conduit.Regarding protective earth there are basically three different systems illustrated inthis page. In SpainTN-SandTTare commonly used. The former most commonly for smaller and residential installations and the latter for larger installations. America usesTN-Cwhich is I thought was absolutely prohibited in Spain but that page says it is allowed if the common neutral-earth conductor has a minimum section of 16 mm2 (that is a diameter of 4.6 mm). That does not sound too difficult to meet but, still, I have not seen it used. What is absolutely prohibited is using metal water or gas pipes for earth. No way.In any case, when doing any kind of work it should comply with local codes, standards and practices so that others can rely on things complying with local codes. When in Rome ...

author: Monkeh
author_rank: Super Contributor
timestamp: March 28, 2019, 01:49:57 pm
content: Quote from: soldar on March 28, 2019, 09:02:30 amNo, they do not use TN-C. If they used TN-C there would be no separate neutral and earth in the installation, whereas the reality is they generally use TN-C-S or TN-S with an additional bond between earth and neutral at the property. In the UK, you will find TN-S, TN-C-S, and TT. Nobody in their right mind uses TN-C outside of distribution.Repeat after me: An MCB is not necessarily an isolator. You must isolate an installation before working on it.Now, if you have appropriate standards in place to use a dual-pole MCB as an isolator, that's fine. But that doesn't make a single-pole device 'less safe', because it is not an isolator..Quote from: Zero999 on March 28, 2019, 08:48:30 amAnd in what situation other than one where you mustisolate the circuitdoes it matter?As a point of terminology, the neutral conductor is always live. That's why it's double insulated and must be isolated before contact.

author: soldar
author_rank: Super Contributor
timestamp: March 28, 2019, 02:11:12 pm
content: Quote from: Monkeh on March 28, 2019, 01:49:57 pmThose diagramsareabout distribution. You might want to go back a look at them again. I think you are misinterpreting things.In America earth and neutral are bonded at the panel.In Spain this is not allowed and earth and neutral are separate wires all the way to the distribution transformer.

author: Monkeh
author_rank: Super Contributor
timestamp: March 28, 2019, 02:14:09 pm
content: Quote from: soldar on March 28, 2019, 02:11:12 pmSo now we're talking about distribution side instead of installation side. Those goalposts move fast. And the relevance to the misuse of a single pole breaker as an isolator in fact still escapes me.

author: soldar
author_rank: Super Contributor
timestamp: March 28, 2019, 02:51:17 pm
content: It is very simple: faults in the circuit, inside or outside, can make the neutral wire become energized. Having circuit breakers which break all poles offers protection against such thing. The Spanish authorities consider this protection significant enough that they require that circuit breakers to break all poles. I understand it and that is enough for me.To the OP my recommendation is to follow local code.

author: Monkeh
author_rank: Super Contributor
timestamp: March 28, 2019, 02:57:44 pm
content: Quote from: soldar on March 28, 2019, 02:51:17 pmIn what circumstance does not having the neutral disconnected by the breaker pose a risk? Merely having it above ground potential is not an issue, because it is a live conductor. You don't have access to it.

author: Zero999
author_rank: Super Contributor
timestamp: March 28, 2019, 03:22:59 pm
content: The goal posts have not moved. If you reread the the thread, you'll remember, it was about distribution from the first page.You forget, we're talking about fault conditions. The system is not functioning properly. If the neutral conductor is still live, it still poses a shock and fire hazard. Under normal conditions, the user will not have access to the neutral, but the case of some equipment could be damaged, exposing it or some insulation might have melted, caused it to be shorted to earth and a high current to flow.The safety regulations are there for a reason, whether you understand why or agree with them or not.

author: Monkeh
author_rank: Super Contributor
timestamp: March 28, 2019, 04:06:14 pm
content: Quote from: Zero999 on March 28, 2019, 03:22:59 pmDistribution = all that stuff outside your house. You know, the stuff controlled by large entities following different regulations. This is about an installation, not distribution.QuoteBut you already said it's not a fused neutral. So you're not offering any protection against combined fault currents from other circuits in an open neutral condition.If the neutral is exposed, you've already passed two layers of insulation (if the upstream neutral is also open, a double fault..). The line could just as easily be exposed - but an MCB doesn't protect against that either, it protects against overcurrent faults, which your body probably will not create. Especially not from an exposed open neutral.If the installation or equipment is damaged youisolate it. A single-pole device is not an isolator, so you use the isolator.QuoteYes, they are, and they are written by people who understand the application of each type of protective device and the circumstances in which they operate, and hopefully applied by people with equal understanding.

author: soldar
author_rank: Super Contributor
timestamp: March 30, 2019, 05:40:06 pm
content: John Ward discusses and explains his very issue:

author: Monkeh
author_rank: Super Contributor
timestamp: March 30, 2019, 05:46:28 pm
content: TL;DW. I know earthing systems.An MCB operates on exactly one fault condition. Please propose a scenario in which it can operate and opening the neutral conductor would be beneficial. If this scenario can be resolved by the use of an RCD (re: TT systems.), or it involves manual operation of the MCB, I refer you to everything I've already said.

author: soldar
author_rank: Super Contributor
timestamp: March 30, 2019, 06:53:26 pm
content: Yeah, there are none so blind as those who will not see.Anyway, it is well explained in that video. For anyone who would like to see.

author: Monkeh
author_rank: Super Contributor
timestamp: March 30, 2019, 07:07:31 pm
content: Quote from: soldar on March 30, 2019, 06:53:26 pmSo explain it.I could go watch 18 minutes of that but I do have other things to watch, so if you'd like to point to the timestamp where he explains the exact fault scenario an MCB sensing only on line would operate in and benefit from opening the neutral, that'd be great.

author: stevelup
author_rank: Regular Contributor
timestamp: March 30, 2019, 07:22:15 pm
content: I agree 100% with you.The sole purpose of an MCB is to deal with an overcurrent scenario. If it opens on overcurrent it has done its job. End of story.

author: Monkeh
author_rank: Super Contributor
timestamp: March 30, 2019, 07:25:25 pm
content: Corner case: Broken upstream neutral, damaged cable withbothline and neutral shorted to earth, potential risk of overcurrent in the circuit neutral via other circuits.The protective device for this scenario is an RCD. If line never shorted the MCB could not clear this fault - an RCD will.Propose other scenarios.

author: perieanuo
author_rank: Frequent Contributor
timestamp: March 30, 2019, 07:28:58 pm
content: Hi, 1p+N if you have triphasic system,otherwise 1PEnvoyé de mon iPad en utilisant Tapatalk

author: Zero999
author_rank: Super Contributor
timestamp: March 30, 2019, 07:55:07 pm
content: 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. 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.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.

author: Monkeh
author_rank: Super Contributor
timestamp: March 30, 2019, 08:05:02 pm
content: Quote from: Zero999 on March 30, 2019, 07:55:07 pmWhen have I implied it's more dangerous?QuoteI 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.QuoteRegulations are behind a paywall, and I am not an electrician. I note you haven't been citing any, either. My reasoning that it is notnecessarily and beneficiallysafer 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.

author: bsdphk
author_rank: Regular Contributor
timestamp: March 30, 2019, 08:11:17 pm
content: 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.Hint: It is not, which is why electrical codes differ.If you live on a mountain, like a lot of Norway do, there is no way you can get a usable earth potential terminal, "ground" and "mountain" are electrically very different things.The electrical code of Norway reflects this, having made intelligent choices in the entire system, to provide the best possible compromise for protection.The "in the entire system" bit is important, personal electrical safety depends on everything the wire is connected to and what kinds of faults and accidents can happen to it.In USA, a very common failure mode is a car hitting a pole and the 5 or 11kV wires on top shorting to the 110-0-110 wires below.This is why USA is so hung up about "surge protectors", and rightly so!In countries where the MV wires are not carried on top of the same masts as LV, class C transient protection is a waste of money because it doesn't provide statistical significant reduction of damage.(And if you are worried about lightning, class C catches fire like anything else, unless you also have tested and maintained class A and B up-wire.)These differences in system failure modes are internalized in the electrical code for your country/region/whatever, and even if you truly understand the systems design decision in your local power-grid, you should still do whatever your electrical code says you should do, because anything else is both A) illegal, and B) reason for you insurance adjuster to laugh.If you want to increase electrical safety in your lab-environment you can do two things: 1) Don't be careless, silly or stupid, 2) Use an isolation transformer until you are sure there are no electrical problems in your DUT./rant offSo answer to original poster: Pick whatever your electrical code tells you to.

author: Monkeh
author_rank: Super Contributor
timestamp: March 30, 2019, 08:23:26 pm
content: Quote from: bsdphk on March 30, 2019, 08:11:17 pmThe 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 memberfrom my own country, I mean, I really could be mixing things up there..

author: Zero999
author_rank: Super Contributor
timestamp: March 30, 2019, 09:02:57 pm
content: Quote from: Monkeh on March 30, 2019, 08:05:02 pmI apologise, I didn't post any standards. I thought Soldar did, but I was mistaken.To clear up the confusion. In many casesa 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.

author: bsdphk
author_rank: Regular Contributor
timestamp: March 30, 2019, 09:09:31 pm
content: 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.

author: Monkeh
author_rank: Super Contributor
timestamp: March 30, 2019, 09:20:01 pm
content: Quote from: Zero999 on March 30, 2019, 09:02:57 pmIn 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 onbothpoles. 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 isolationfor servicewithout 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 pmThey 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.

author: bsdphk
author_rank: Regular Contributor
timestamp: March 30, 2019, 09:35:05 pm
content: "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

author: soldar
author_rank: Super Contributor
timestamp: March 30, 2019, 09:39:37 pm
content: I believe the advice to "follow the code" has been repeated several times in this thread.Quote from: Zero999 on March 30, 2019, 09:02:57 pmI was just watching Mains Supply And Consumer Unit and that is very different than what we have in Spain. Here the "Mains Supply" cabinet is outside the housing unit and not accessible to the tenant, only to the power company. So the main breaker in the "consumer unit" is what would be used to isolate the installation from the outside.ETA: BTW, using wood in the mains panel would be totally illegal here. Sounds crazy.

author: Monkeh
author_rank: Super Contributor
timestamp: March 30, 2019, 09:43:51 pm
content: Quote from: bsdphk on March 30, 2019, 09:35:05 pmI can't speak for the rest of the EU (and probablyreallycan't soon), but here it is a.. grey area. Unless they've tightened their grip more since I last checked.They are trying very hard to make it illegal or impractical for people to perform their own work, but this is mostly driven by several large private organisations withimmensevested interest in their own profits. But that is very much outside the scope of a technical discussion.QuoteFrom my perspective it appears to simply be poorly thought out standards. But they are old, and improving them or adopting anyone elses ideas is heresy there.

author: Zero999
author_rank: Super Contributor
timestamp: March 31, 2019, 08:47:40 am
content: To answer the question: why 1P+N, rather than 1P? The main reason is sometimes it's necessary to isolate an entire circuit, so it can be maintained, without shutting everything down. Granted, an isolator can be used as well as a circuit breaker, but if the two are combined into one, it saves cost. It's also safer because two contacts will break the arc more effectively than one and for the reasons mentioned above regarding broken neutrals.

author: Monkeh
author_rank: Super Contributor
timestamp: March 31, 2019, 01:43:52 pm
content: Quote from: Zero999 on March 31, 2019, 08:47:40 amSo the first point would be the non-safety maintenance point I admitted. No cost is saved by using 1P+N breakers as you still need to isolate the supply to them, so you have an upstream isolator anyway. This is not really a useful thing in a domestic or small commercial environment, just a waste of space and additional points of failure.The second.. the breaker is required to safely clear arcs up to its interrupt current rating, and I can't see how you can say it's objectively safer to have a breaker which meets a standard than another breaker which meets the same standard.As for the third point, I still do not see a fault scenario in which it is objectively safer to disconnect neutrals in an overcurrent condition. A different device is required to protect against lost neutrals.

author: Cubdriver
author_rank: Unknown
timestamp: March 31, 2019, 02:56:11 pm
content: Quote from: made2hack on March 26, 2019, 09:02:05 pmSince I didn't see this answered subsequently in the thread, I'll chime in here - this is one that will depend on your local electrical code.For instance, here in the US, you CANNOT by code bond the neutral and earth at a SUB panel - earth and neutral are to be bonded together at the service entrance/main disconnect (where the mains enter the building,usuallythe main breaker panel, but not always if for some reason it is located more than a few feet from the service entrance). Any panels that are remote from the main disconnect/earth-neutral bonding point must have separate neutral and earth conductors run to them, and their neutral and earth buses must be kept isolated as well.So in short, for this answer check the applicable code for your area.-Pat

author: Zero999
author_rank: Super Contributor
timestamp: March 31, 2019, 07:13:40 pm
content: Quote from: Monkeh on March 31, 2019, 01:43:52 pmYou've missed the point. What if you need to work on the circuit connected to the other side? Suppose an outbuilding is wired on a separate 1P+N breaker and you need to work on a circuit in there? No need to turn off the whole house, just isolate that circuit. You've saved money by having the breaker and separate isolator.Did you know that connecting two relay contacts in series can double the voltage rating because it quenches the arc more effectively?Just because you cannot see it, it doesn't mean it isn't so. Reread the thread.

author: Monkeh
author_rank: Super Contributor
timestamp: March 31, 2019, 07:34:44 pm
content: Quote from: Zero999 on March 31, 2019, 07:13:40 pmI have not missed the point, you simply see a huge inconvenience where most people do not.QuoteAnd under which standard is this tested and acceptable? Again, the device is designed to be capable of clearing any fault it should reasonably expect to encounter in service.QuoteI have repeatedly asked for you to actually detail the scenario, instead of just repeating "broken neutral" like a mantra.I shot down the theory of a high fault current through neutral shorted to earth, as a 1P+N MCB cannot clear it, and likewise it cannot be relied upon to protect from contact with broken neutral at high potential becausethis is not what MCBs do, RCDs are the protective device for human contact, as well as neutral to earth fault currents.

author: ruggedscot
author_rank: Newbie
timestamp: March 31, 2019, 07:50:29 pm
content: A little knowledge is a dangerous thing - messing with electricity if you don't fully understand or appreciate what you are doing is lethal...The electrical supply to your house can be given in a number of configurations.TN-C is a configuration of supply where the Neutral and Earth is combined - in this configuration the neutral must not be switched.its worth reading up on how electricity is supplied and then checking to see how your installation is configured. Don't assume and don't take advice from forums where there are people out there that don't know how your electrical supply is configured.With a TN-C-S configuration the earth and neutral are combined and then separated through to the point of connection - this type of supply both the neutral and live can be switched. The main issues around switching a neutral is that if you don't you can have a situation where the live is switched off but the neutral is still connected through to the item that you are working on. Depending on other loads in the area that is being supplied and the impedance of the wiring you could have a voltage drop between the source neutral and the loads. this could then produce a voltage on the neutral that is above the potential of earth. So you could then have a potential for a current flow between the neutral and the earth in the event of an inadvertent contact between the neutral and earth.https://electrical.theiet.org/media/1549/earthing.pdf