HELP! reverse polarity

[0075]

one of our walllights was connected with live and neutral reversed which seems to have blown the light fitting. i tried another light fitting in its place but that not working either. (an electrician also did the same thing and blew our fan in the bathroom, then denied ever doing the job!!)..the light in question is connected to two gang two-way switches, one upstairs and one down. the light downstairs works ok but nothing out of the new upstairs light. the mcb didn't trip.

don't know much more about electrics and the damaging effects of reverse polariy..maybe someone could explain/help?

cheers

 

[P.S.]

is this a trick question ?

 

[ericmark]

A light fitting would not normally blow because line and neutral are swapped they are after all both considered as live.
When you start to talk about up-stairs and down-stairs I start to wonder if it’s a RCD that is tripping?
There has been a few problems of late when properties wired years ago when we used two core cable as strappers on two way lights have been up-graded to a new consumer unit that has RCD protection on the lights and the “browed neutral” caused by only using two instead of 3 wires with strappers it turn causes the RCD to trip with some combinations of the two way lights.
But the information you give is not enough to work out if this is what is going on in your case.

 

[0075]

P.S. - thanks but if i had all the answers, i wouldn't be on here..unless i wanted to laugh at people who didn't know..the 'electrician' who i employed gave me this explanation but he was obviously full of crap in the first place as he broke my appliances..and i am hesitant to get another 'professional' out to charge me over the odds for poor work..

Ericmark - thanks for being more helpful..i know nothing about electrics except how to change basic fittings..i live in a old building but it was converted about 6 years ago and is a social housing scheme so all wiring new and to a high standard..what more info would you need to help?

 

[P.S.]

Sorry, it's just that domestic power is AC and by its very nature doesn't have a defined polarity as it alternates 50times/second. That said, Live and Neutral should be kept as such, throughout the wiring.

If you think about a standard bulb, (bayonet, push and twist) it has the two terminals on the bottom, so taking a bulb out, turning it 90 degrees and replacing it has no effect on it working, even though the terminals now connect to the opposite connections in side the lamp holder... Same as the old cassette type "figure-eight" plugs...

You can fit them either way round....just like you can plug a "shaver" lead in, any way round into the socket...it matters not ./... any end appliance, lamp, radio, washing machine etc etc will work no matter what way round the L & N are, but it's good practice to wire them correctly.

 

[00775]

That's ok..i'm just quite frustrated as i think it is something really simple that has gone wrong but don't know enough to correct it..

..I basically changed all the wall lights to nicer ones and they were all working OK (2 are on one circuit which are fine and the broken one is on a different circuit)..i then removed the now faulty light so that i could fill in some gaps left from the old fitting..when i went to reconnect the light, it wouldn't work..i also tried the old fitting and that wouldn't work either. can't see any loose connections

any ideas?

ta

 

[00775]

P.P.S. the fan is a separate issue and the electrician said that reverse polarity had caused it to blow (so i assumed this was the same with the lights)..but he wouldn't give me a thorough explanation and was pretty anxious to leave..i didn't realise at the time but it was an expensive fan that he obviously didn't want to replace..then he denied ever coming round..so i'm pretty annoyed about that..i thought i would consult you lot who seem to know what you're talking about before getting anyone else out..

 

[Taylortwocities]

You need someone on site who has some kind of come-back.

Have a look on www.competentperson.co.uk for local bod.
They are all members of registration schemes - most of these have customer guarantees so you'll be able to call their reg body if the sparky doesn't come up trumps.

But please don't expect a queue at your door of sparkies wanting to sort out somebody else's mess.

 

[Spark123]

but it's good practice to wire them correctly.

Not only good practice, is essential that some of the lamp holders i.e. the older edison screw have the centre pin wired to the phase, also for things like fuses and switches etc which need to be in the phase conductor and never in the neutral (unless they also switch the phase).

 

[rebuke]

Sorry, it's just that domestic power is AC and by its very nature doesn't have a defined polarity as it alternates 50times/second

That's not exactly true - while both the line and neutral are live conductors, if everything is wired correctly, neutral should be at 0V, and the line wire should alternate between -230 and +230V. It's not strictly speaking a polarity I guess, but there is a definite distinction. This is why it's safe to isolate a circuit by just switching off an MCB, as while this only breaks the line conductor, i.e. leaves the neutral connected, the neutral should be at 0V, so you shouldn't get a shock off it (yes there can be issues with neutral to earth shorts tripping RCDs etc etc...)

 

[sm1thson]

Pedantic bit:

That's not exactly true - while both the line and neutral are live conductors, if everything is wired correctly, neutral should be at 0V, and the line wire should alternate between -230 and +230V.

isntit more like -325V to +325V the average of which would be 0V hence we use RMS giving 230V(ish)

That's ok..i'm just quite frustrated as i think it is something really simple that has gone wrong but don't know enough to correct it..

..I basically changed all the wall lights to nicer ones and they were all working OK (2 are on one circuit which are fine and the broken one is on a different circuit)..i then removed the now faulty light so that i could fill in some gaps left from the old fitting..when i went to reconnect the light, it wouldn't work..i also tried the old fitting and that wouldn't work either. can't see any loose connections

any ideas?

ta

how man wire/cables are there? whats connected to what and with what?

 

[00775]

there are two wall cables, one with black and red, the other with black red and earth. Both red wires have been capped off..the earth and two black wires connected to a junction box which is connected to live and neutral and the earth to the earth..then live, neutral, earth into the light fitting..the fitting did specify which way around they should go.

i checked all the wires for loose connections..when i looked at the black wires, the wire was still covered with it's sheath ie not exposed like the other wires..it had just been cut and slotted into junction box..

thanks everyone for your help and for the competent tradesman site..very useful!

 

[ericmark]

OK 0075 since such a new house unlikely that the two way lighting is wired wrong. Also since you have removed and refitted a light would seem likely you have disturbed some cables while doing it. The bathroom fan could be blown by wrong connection but very unlikely and from other posts seems they are not very reliable at best of times with many complaining of premature failure.
When British light fitting are replaced with continental light fitting one is left with the loop wires with no termination point, it is common to hide these in the ceiling space and I would guess that is what has happened and you have disturbed them causing a disconnection likely a good lamp is where bad connection is.
You need an electrician and you need to tell him exactly what you have done so he will know where to check including lamps removed and refitted that still work as fault is likely to at those lamps.

 

[matt1e]

Sorry, it's just that domestic power is AC and by its very nature doesn't have a defined polarity as it alternates 50times/second

That's not exactly true - while both the line and neutral are live conductors, if everything is wired correctly, neutral should be at 0V, and the line wire should alternate between -230 and +230V. It's not strictly speaking a polarity I guess, but there is a definite distinction. This is why it's safe to isolate a circuit by just switching off an MCB, as while this only breaks the line conductor, i.e. leaves the neutral connected, the neutral should be at 0V, so you shouldn't get a shock off it (yes there can be issues with neutral to earth shorts tripping RCDs etc etc...)

not exactly correct either

line and neutral have exactly the same voltage on them with respect to each other its just that one of them is connected to earth (neutral) so between line and neutral/earth we have 230v and between earth and neutral 0V because they are at the same potential

isntit more like -325V to +325V the average of which would be 0V hence we use RMS giving 230V(ish)

-325V to +325V is correct peak to peak but we use the rms value of 325 which is 230 (325 divided by the square root of 2 =230)
as this gives us the equivalent value of power that a dc supply would give at 230v

hence we can make ohms law etc work on our ac circuits

 

[00775]

ok, just to be clear..you think the fault is at the good lamps rather than the one that doesn't work? its a bit confusing as the two good lamps seem to be on a different circuit to the one that doesn't work..

good to know about the fan being temperamental but the 'electrician' who came around also gave me a false name..i found out afterwards when i did some investigation..so i can't help thinking he had something to do with that particular problem..you live and learn though!

but i can now hopefully find myself a skilled person..