live and neutral reversed question.

[mattysupra]

hello all, i wonder if some one can help me understand this question. ( im not a electriction but like to learn!)
What is the reason that we have to put the live and neutral a certain way around in the u.k?

The bit that i dont understand is that when abroad you have a two pin plug that you can put in a socket either way around so this must reverse the neutral and live does it not?

Also when last at my place abroad i had to fit a new socket and took my tester with me that checks for earth, neutral and live faults ( cant remember the name of the thing but is a black square with 3 lights on the front with a u.k plug molded into it ) Now when i pluged it in it showed 3 lights to indicate the plug was wired correct, so i turned it upside down but it still showed all 3 lights saying that all was wired correct! how is this possible if it can tell if the live and neutral are the wrong way around?

 

[Spark123]

We fit protective devices (fuses etc) in the live (phase) conductor.
If there is a fault, we want the fuse to pop and disconnect the supply. If the fuse is in the neutral it may pop with a phase to neutral problem but the system still remains live at 230v. This can leave a faulty appliance live.
There is another problem here as we fuse the supply down locally in the plugtop. If there is a phase to earth fault this small fuse protects the cable downstream of it. If there is no fuse here i.e. phase and neutral reversal then the larger fuse/mcb upstream needs to disconnect the fault meaning the smaller cable can take a large current for longer than it is designed for.

 

[mattysupra]

i think i understand, when working in the cu (had to change the mcb as had a 20 minute delay with a fault!!!!) i noticed that the rcd's had both the neutral and live going through them, like a double one of ours that have our live only going through. So i take it that it trips either way ?

But also why does my tester still say the connection is the correct way even if reversed?

 

[Spark123]

RCDs are a different device to a fuse or an MCB. An RCD looks at the current flowing through the phase and returning via the neutral. If these remain ballanced the trip stays healthy. If they differ by the rating of the device then the trip opens, cutting the supply. Some RCDs have a MCB built in and are called RCBOs, some of these type only trip the phase conductor.
I'm not sure as to why your tester will register healthy abroad, what type of system do they use? Is their neutral tied to earth?
A lot of foreign countries use radial socket circuits with a smaller fuse at the CU, the Ring Final is a british thing!

 

[mattysupra]

from what i could work out the system is a radial not a ring, wires go every where and dont seem to be a ring at the rcd or what ever it is. The breakers also loop together in a radial. So basically the 4mm wire powering the first breaker then links to the next and the next and so on. I cant work out how it takes the load without setting fire! Maybe because its such a sort piece of flex? maybe 4" long?
More to the point the lights are on a 32amp breaker, i thought about changing it to a 6 amp but then realised that some of the sockets come off the lighting circuit!
We had a full servey of the place before we brought the place and its only about 10 years old, the electrics where up to there standard

 

[Spark123]

I'm not genned up on foriegn wiring systems so can only comment in general - 32A does seem to me to be a bit big for lights, could it be a feed to another CU? Which country are you talking of?
A local spark with a good knowledge of their systems is a safer bet!

 

[mattysupra]

tenerife, as for the local sparks! Forget it. When we got one out to find out why the mcb keep tripping every 20 mins, he plugged a kettle in, turned it on and as it did not trip he said there was nothing wrong with the electrics and it is normall for them to trip off from time to time . then i got another spark out to fit the electrics for a aircon unit i was fitting. He put 1.5mm cable in on a 40 amp breaker with no earth, so i kicked him out half way through the job! Next i got another spark out to see why we kept getting a shock off the freezer, He turned up touched it a couple of times fast and said this is fine also! I did find that the fridge had a earth on its plug but it was not conected at the socket, i know that this has not solved the shock problem but at least it has a earth now so im guessing it should trip the new mcb if a problem?
P.s the reason for the new mcb was as it kept tripping every 20 mins i decided to change it incase this was the fault, after fitting the new one it would not let me switch it on so then i went round trying to find the fault, turns out a completly melted back of the socket along with wires in the bathroom about 1meter away from the sink!

 

[Spark123]

You need a good local spark!!
Maybe worth asking around, see if you can get any recommendations.

 

[mattysupra]

these people where recommened as the best on the island Tenerife really is eye opener when you watch them work. I have considered re wiring the place to british spec but then it would be wrong in there eyes! The health and safty is deadly and there seems to be no sort of qualification in anything, i think if you can put the batterys in a torch the correct way around you pass as a spark!
Put it this way, my sisters fella drives a coach from the airport to the hotels dropping us british off on our holiday, he is contracted to do a minimum of 12 hours a day on the road but does 14 hours to keep his job, with 60 passengers life's in his hands, o and after he has finished driving for 14 hours he has to clean the coach before he can go home!