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Message started by Beanzy on Jan 10th, 2005, 9:09pm

Title: Reversed live and neutral
Post by Beanzy on Jan 10th, 2005, 9:09pm

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.

Title: Reversed live and neutral
Post by L.Spark on Jan 10th, 2005, 9:19pm


Quote:
To whichever person removed it I'll just say that's not conducive to running a good forum


Sorry but if he wants to have a moan then he can go elsewhere and do it, if he wants to ask for serious advice then he can do so without the digs, we had all this before and we don't need it again.

Title: Reversed live and neutral
Post by Damocles on Jan 10th, 2005, 9:26pm

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.

Title: Reversed live and neutral
Post by L.Spark on Jan 10th, 2005, 9:29pm


Quote:
you claim to be a useful resource used by PROFESSIONALS


Don't know who said that


Quote:
I have had seriously better comments from you know where forums


Then go there instead


Quote:
I posted a serious question about a serious matter of safety here


Well you have your answer, see first post

Title: Reversed live and neutral
Post by Damocles on Jan 10th, 2005, 9:30pm

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.


Title: Re: Disappearing post from Damocles?
Post by Beanzy on Jan 10th, 2005, 9:37pm

Listen LS I don't want to be here replying to posts which are deleted 1/2 way through my attempts to answer them just because someone gets the pip with another. Damocles may annoy you but it's not necessary to delete posts just because they irk. That's mixing up personal preferences with your role as a Forum Admin, and insults those who want to use the Forum freely. If you feel This is not the case then please let me know on here so I can make up my mind about the appropriateness of bothering to reply to posts.

Title: Re: Disappearing post from Damocles?
Post by L.Spark on Jan 10th, 2005, 9:41pm


Quote:
If you feel This is not the case then please let me know on here so I can make up my mind about the appropriateness of bothering to reply to posts


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


Quote:
Damocles may annoy you but it's not necessary to delete posts just because they irk.


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


Quote:
That's mixing up personal preferences with your role as a Forum Admi, and insults those who want to use the Forum freely.


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.

Title: Re: Reversed live and neutral
Post by Beanzy on Jan 10th, 2005, 9:49pm

The problem is that no matter what background history you may know, a post is a post and should be treated on its' merit. The post in question was tetchy but made no insults except to say that other fora were better for quick replies; that's why I began my answer with the dig at Damocles being impatient. But that should be the cut and thrust of posting, this isn't kindergarten.

Title: Re: Reversed live and neutral
Post by Damocles on Jan 10th, 2005, 9:50pm

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.

Title: Re: Reversed live and neutral
Post by chtechie on Jan 10th, 2005, 10:16pm

Know how you feel Damocles - Had a similar problem where a qualified spark had reversed the tails into the CU - He told me I didn't know what I was talking about (well something like that) when I pointed out the error of his ways fortunately I don't have to work with him !

Title: Re: Reversed live and neutral
Post by Beanzy on Jan 10th, 2005, 10:18pm

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.

Title: Re: Reversed live and neutral
Post by plugwash on Jan 11th, 2005, 4:11am

ok lets consider this rationally what are the real dangers of reversed live-neutral.

switches inside appliances? maybe but remeber MOST OF EUROPE DO NOT HAVE POLARISED SOCKETS.

switches on sockets? may be more of an issue if they are single pole.

all switches: how is switching the wrong side of an appliace leaving it in any more danberous a state than if its simpl left on (which is done all the time by householders)

Fault to earth: this is the biggest danger as overcurrent devices will be in the wrong side. However if an rcd is present then it should cover this situation.

Sure its not ideal to have live and neutral reveresed but making it out as an imminent danger to the users of the install is a GROSS EXAGGERATION.





Title: Re: Reversed live and neutral
Post by Beanzy on Jan 11th, 2005, 5:01am

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.

Title: Re: Reversed live and neutral
Post by John   Davies on Jan 11th, 2005, 11:59am

Surely, there are two possible courses of action.  

Firstly, point the mis-wiring out to the installer concerned.  If they put it right, well and good.

If they laugh it off, then either the householder or the firm employing the installer should be told, for safety's sake.  However, I don't feel that this would necessarily be the first course of action - why get someone into trouble for a simple mistake, we all make them from time to time, and if they are pointed out to us we tend to get more careful rather than the reverse.    

Whatever, the matter can't simply be left alone.   The possible consequences of leaving alone are potentially lethal - years ago I had a nasty shock from a miswired circuit  and wouldn't wish it on anyone else.  The golden rule is to always assume any wire you may be working on is live.

John Davies
 

Title: Re: Reversed live and neutral
Post by didds on Jan 11th, 2005, 12:52pm

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.

Title: Re: Reversed live and neutral
Post by billythekid on Jan 11th, 2005, 2:40pm

If the switches had been double pole this couldnt have happened right? Do sockets come with DP switches?

Title: Re: Reversed live and neutral
Post by zambezi on Jan 11th, 2005, 3:16pm

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!! :o

Title: Re: Reversed live and neutral
Post by didds on Jan 11th, 2005, 3:29pm

Billy,
I'm sure Crabtree are single pole,so I just tested one, and yes it is. I know Select is double pole, and guaranteed for 15 years, Not as pretty, but safer and cheaper.

Title: Re: Reversed live and neutral
Post by billythekid on Jan 11th, 2005, 3:33pm

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

Title: Re: Reversed live and neutral
Post by zambezi on Jan 11th, 2005, 3:49pm

When did they ever do anything that made sence?? Maybe if the gov owned shares in MK, Select etc they would consider making it a new law.

Title: Re: Reversed live and neutral
Post by didds on Jan 11th, 2005, 3:51pm

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.

Title: Re: Reversed live and neutral
Post by Beanzy on Jan 11th, 2005, 3:53pm

The Gov't don't spec it, it's BS, oh yes those very same ones who run such a reasonably priced scheme for Domestic Installers. All Part P says is do it to B$7671 and pay us the dosh. So if the IEE can be wangled into requiring pink fluffy outlets in kitchens then that'll go in. BSi may then change the standard if the others are seen to be obsolete.

However it's not going to make a reverse polarity safe to use, just safe when switched off.

I'll shut up now as my name appears way too often in this post and I'm getting bored with the sound of my own keyboard.  :-*

Title: Re: Reversed live and neutral
Post by plugwash on Jan 11th, 2005, 4:23pm

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.


Title: Re: Reversed live and neutral
Post by L.Spark on Jan 11th, 2005, 4:50pm


wrote on Jan 11th, 2005, 3:49pm:
When did they ever do anything that made sence?? Maybe if the gov owned shares in MK, Select etc they would consider making it a new law.


MK logic Plus Sockets are all double pole.

Title: Re: Reversed live and neutral
Post by plugwash on Jan 11th, 2005, 6:02pm

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.


Title: Re: Reversed live and neutral
Post by Damocles on Jan 11th, 2005, 7:32pm

Well in this case there is an RCD (though I did not personally check the wiring). Which must help. As has been pointed out, there are guys on the continent merrily getting by with reversed voltage each time they pull out and replace the plug.  RCD should deal with shock in the event of someone discovering it was live when he thought it switched off.

I agree Beanzy, it is a pretty basic principle to get the wires the right way round. Thing is, once upon a time this might have been your only safety device-knowing which one was live- but now it is not. So bearing in mind that the question is not whether the regulations have been followed to the letter, but whether the installation is safe, it seems necessary to think carefully.

It is beginning to sound as though this might actually squeak through as being safe. The plug fuse is not isolating live, 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.

??

Title: Re: Reversed live and neutral
Post by chtechie on Jan 11th, 2005, 7:57pm

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 .........)

Title: Re: Reversed live and neutral
Post by Damocles on Jan 11th, 2005, 8:17pm

Yeah, that is the kind of thing I was interested in. Whether there really is equipment out there wich is polarity sensitive. (as well as people)

Title: Re: Reversed live and neutral
Post by Beanzy on Jan 11th, 2005, 8:39pm


wrote on Jan 11th, 2005, 7:32pm:
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.


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.

Title: Re: Reversed live and neutral
Post by plugwash on Jan 11th, 2005, 10:02pm


wrote on Jan 11th, 2005, 7:57pm:
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 .........)

got references for that?

and did they mean it doesn't work if L and N are reveresed at the boiler or if L and N are reveresed for the system as a whole (there is a BIG difference)

if it doesn't work with L and N reveresed for the system as a whole then it means that somewhere it is connecting something between live and earth which is rather dodgy to say the least.

Title: Re: Reversed live and neutral
Post by Lectrician on Jan 11th, 2005, 10:08pm

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

Title: Re: Reversed live and neutral
Post by plugwash on Jan 11th, 2005, 10:43pm

lectrican was that with just the boiler on reverse polarity or the whole CH system?

Title: Re: Reversed live and neutral
Post by chtechie on Jan 11th, 2005, 11:14pm

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"

Title: Re: Reversed live and neutral
Post by Lectrician on Jan 12th, 2005, 6:25pm

Just the boiler.  Everything else worked fine.

The story....

First fixed and second fixed a house.

Cent heat wired to the CU via an FCU.

Plumber wanted to commision, and without asking, disconnected the FCU and wired it directly to a plug top to power the whole cent heat circuit.

I didn't get along with the plumber to begin with, as we had 'stolen' his sons job (quote was cheaper ;)).

The system didn't fire up.  The valves worked, the pump fired etc etc, but the boiler didn't fire, and showed an error.

The plumber got his son to have a look with out ringing us.  His son found the live and neutral reversed at the boiler(as in the flex brown was neutral, and the flex blue was live  :o).  Without removing any other covers, he put the blue into the live terminal of the boiler and the brown to the neutral. (dick head).

The plumber couldn't wait to throw abuse.  I new I had done it properly.  Can't get a lot wrong with colours!!!!

The first thing I tried was the extension lead he had plugged the whole system into - It was reverse polarity (good old plug-in martindale socket tester ;)).  Checked the site temp supply socket that the extension was plugged into - all ok.

The extension was wired with reverse polarity in the trailing end.........The plumbers son had made it up from some old flex and a plug and  trailing socket  ;D

That was a great day, I made sure I kept abusing the plumber all day - As he had to me when I first arrived of site  ;)

Title: Re: Reversed live and neutral
Post by bripl on Jan 12th, 2005, 7:35pm

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. ::)

Title: Re: Reversed live and neutral
Post by Lectrician on Jan 12th, 2005, 8:06pm

Well there we have it guys...

My plumber was still a tosser!

Title: Re: Reversed live and neutral
Post by billythekid on Jan 12th, 2005, 10:03pm

i agree, most plumbers are!

Title: Re: Reversed live and neutral
Post by scotspark on Jan 13th, 2005, 8:08pm

Had exactly this problem when In a rush fitting a new consumer unit in a horrifically akward space I connected the tails up reverse polarity :-[ :-[ :-[ :-[ :-[ and didn't test until the next day cos i had to rush off and my martindale had got broken the previous day.

got there and the customer mentioned thety had no hot water or central heating :-[ :-[ :-[ :-[

not one of my finer moments.


why do you think he done it deliberately DAMOCLES?????? it's asimple mistake to make as different sockets have connections on different sides, but he should have picked it up when testing

Title: Re: Reversed live and neutral
Post by ban-all-sheds on Jan 17th, 2005, 12:43am


wrote on Jan 12th, 2005, 7:35pm:
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. ::)

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?

Title: Re: Reversed live and neutral
Post by plugwash on Jan 17th, 2005, 8:47am

all i can think of is it could be relying on thier being a voltage between neutral and earth possiblly for some sensing arangement.

or its a deliberate miswiring cutout for some reason.

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