I was posting this reply to a post about reversed L&N from Damocles, when the topic seemed to disappear......... in case it never comes back here's my reply. To whichever person removed it I'll just say that's not conducive to running a good forum if posts get deleted during times whan people are most likely to be using the reply. Please Post a warning that you may be doing this and give it a decent span of time before you do.


The answer;


I'll tell you what from now on I'll hang about all day just incase you happen by. I may give up work just in case

No seriously different folks will be on at different times. And it's a propper answer you need rather than the quickest.

The reversed L-N can be fatal, it's one of those no if's and buts situations. The reason why is because when you switch off the appliance at the switch it will remain live even though the circuit will of corse not be completed. If there is a fault, or a casing got damaged etc then there could be a full 230v waiting to whack someone. Also if you switch off the TV or appliance at the socket at night, it could sit there with the power back-feeding into the TV all the while.

As for what you should do. Call the installer/builder and ask to see the test results. If there are none ask why. If your contract with them said they'd do the electrical installation as part of the build, and it's faulty/potentially lethal, then you have the same come-back as you would with any other purchase of a service or product which is unsuitable for the purpose. Find out how much of the build cost was for the electrical installation, then pursue it with the Consumers Association or your Local Trading Standards people.

The solution is cheap enough in that extentions can be crimped to the existing short wires (done properly not with those dodgy squishers you see sold. Although this is a simple fix, they could have killed you and that's the bit that should worry you most.

I posted a serious question about a serious matter of safety here. The work was knowingly done wrongly by another electrician, not me, and he will likely be back. I have the awkward problem of telling his employer (also mine) what he has been doing. I do not regard this in any way as a frivolous matter, and I posted here because you claim to be a useful resource used by PROFESSIONALS.

I posted some follow ups because I could see the post had been read, but with as yet no answers. I have to resolve this tonight.

I have had seriously better comments from you know where forums.

Oh, and thanks beanzy.

The point is, he did it on purpose. So i really do want a whys and wherefores of how this might be justified. Or not.

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No you can carry on replying as you wish, that's up to you Beanzy, I will enlighten you about the rest.

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He doesn't annoy me, he just causes problems.

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Moderator & my job is to keep the forum clean from any rubbish that might get posted, Insult's to the people who use the forum are to let it remain.

Trying to get an answer here is likle being on a roler coaster. One minute your post is up, the next its down...

Thanks, I have had some useful and I guess decision making replies elsewhere already.

I thought the forum founder said he wanted it to be a useful resource for the public. I would hunt out the post, but it was deleted.

I shall start again, but I doubt there will be time to recieve any replies.

I today came across some replacement sockets in someones kitchen which had been deliberately wired up with n and L reversed, because the cables were too short to reach  the new screw positions. The guy who did this is experienced as an electrician though currently working as a general builder.  Tomorrow I shall most probably have to point out what has been done, as tactfully as possible. But stressing the most important points.

I know perfectly well this is not a good idea. However, I suspect it is in reality not as bad an idea as it first appears. If you guys, as professionals, actually sit and think about how the consequences might pan out.

So I was hoping for some informed comments.

There is very unlikely to be any documantation. The most expedient thing for me to do would be to say absolutely nothing and pretend I never saw it.

Like I say it's potentially fatal. That's what the regs are there for. Polarity is one of the most basic tests for just that reason.
As for whetere it'll normally matter; The circuits have to be designed for fault conditions, not best case scenarios. It's normally only under a fault that electrical problems arise. As the fuse is in the Neutral any fault to earth will not pass the fuse, although as it's a local reversal it will be limited to the overload passing current of the 32A MCB. the circuit under fault conditions will be live to earth with up to a steady 32A cooking the flexible cable and components of anything connected, not to mention the person making contact with any metalwork or the faceplates.
Lethal.

A fault to earth won't pass though the appliance fuse so your flexible cable can be loaded with the full circuit current (we'll it'll melt on the way there). Nasty

The equipment remaining live when switched off at the wall and the user assumes it's safe isn't good. When you switch something off at the outlet you would expect the power to the appliance to be cut off. People do this kind of thing all the time where they switch the TV off but don't go to the faff of unplugging it overnight.

There doesn't have to be an RCD on the circuits, but if there is and you switch the neutral, you may get nuisance tripping due to the imbalance across the load. It would be similkar to when you get a faulty 2 pole switch which disconnects the neutral a fraction early. They trip out RCDs.

As for the rest of Europe (except the old sod) they've been sitting on dodgy practices for years. I'm not going to enourage us to follow suit.

Hi Lads,
Recall an incident not so long ago, that a DIYer wired his neighbour's house. Reversed polarity on ring main supplying the lounge.
Electric fire plugged in to socket, but the switch was in the off position, young child put hand through grill, touched end of element, died. It made the papers.
So, definitely a no no.

This is a common problem when poeple mixed up live and neutral (mostly people fitting the plug incorrectly).

Toast gets stuck in toaster, you know it bites if you stick your knife in to dig it out, you turn off the switch, insert your knife and get the shock of your life!!

why dont the government specify only dp switches then, this would seem a safer thing than part P!

Billy,
What about lighting circuits that are not protected by an R.C.D? Install D/P switches? The switches are single poled at the moment, so it would mean changing existing wiring, and how some sparks would have to change their methods of installation in the future.
Correct polarity is the answer.

aparently in some parts of spain the polatiry at the intake point swaps every few weeks but i digress .

some parts of europe also have installations that are supplied from 220V line-line services.

It is perfectly possible to design stuff to be safe with live and neutral either way round and most portable appliances are designed this way to make them safe accross europe (where nonpolarisaed plugs are the norm). It is possible to do the same for fixed wiring and the caravan regs essentially require this.

the fact is we brits seem to get upset at people trying to suggest that the IEE regs are anything less than gods commandments. We won't for example adjust our sockets to take europlugs (all it would involve would be adding a fuse and adjusting the shutter design nothing more) even though the whole of the rest of europe and most other countries that use the same voltage band have made sure thier sockets can take the things.

i think thats his point. If the compaines that already make all dp sockets had influence in goventment then the goverment might push it as a requirement.

Safety aside there are a number of CH boilers on the market which don't work if L & N are reversed. (Baxi Solo, Glow worm Ultimate .........)

[quote author=Damocles  link=1105391377/15#25 date=1105471938] but it will anyway only cover cases of n-l short in the range 13-32A. Less or more than that either would not have been covered anyway, or should trip the mcb. I know this is not ideal. But it is not a million miles away from normal continental practice, which does not kill huge swathes of the population over there. [/quote]

I don't understand why you discount the fuse in protecting a L-E fault? That's why we measure Zs to make sure it will disconnect in time. As I said earlier, the fault will pass to earth, through the high resistance (the poor bugger toucing the shiny faceplate), or through the faulty equipment with that resistance. It may never even dead short, so could pass 30-36 amps for one heck of a time. By then the person is either dead or the flexible cable has started a fire. How would this be safe? I'm not taking into account whether this will happen or not, it can happen and probably would happen in the event of a fault, 32A is a heck of a load for a .75mm flexible.

The real concern I would have here is that there is a known fault with the sysyem, which is potentially fatal, so how can it be ok to leave it? or try to talk a way around it? Surely it would be a bit callous if they were to leave it for someone else to cop it, just for the sake of getting it sorted properly. I wouldn't sleep well knowing there was a bodge job there waiting to kill. Look at the infamous MPs daughter scenario and that was just a cable zones/ protection issue.

I know of atleast  one make of boiler that will not fire on reverse polarity - long story Plug - I will tell it another day

Hi PW

Sorry been busy doing other things - If you reverse the L & N to certain boilers they do not fire up - I've worked on both standard boilers and combis which behave like this - I quote from one manual (Baxi Solo) "Polarity of the appliance must be correct otherwise the appliance will not work correctly"

as a humble plumber ithink i should point out most modern boilers which contain a pcb will not operate with reverse polarity something to do with the ignition and flame sensing device.

i agree, most plumbers are!

[quote author=bripl  link=1105391377/30#34 date=1105558514]as a humble plumber ithink i should point out most modern boilers which contain a pcb will not operate with reverse polarity something to do with the ignition and flame sensing device. [/quote]
It's an AC supply, the voltage between Live and Neutral will vary between +325V and -325V 50 times a second whichever way round it's connected - how can it make a difference?