HELP! reverse polarity

[ericmark]

Because of the loop system we use where the DIY'er starts to play it is common to find the fault at a lamp that works.

Remote from the job I can't say if this is the case with your set-up. But often the house holder does not give the electrician full story until after it is fixed and in doing so get a bigger bill as it took the electrician longer to find the fault which is why I said tell the electrician all you have played with including those that work to keep your bill down.

 

[00775]

yes of course but there's nothing much to tell the electrician..other than i changed the light fittings over which isn't a massive DIY challenge (even for me!)..two worked fine..and so did the one that is now working..then i took the fitting off to replaster and when i put it back up, i was rushing it a bit and got neutral and live wrong way round (durr!)..when i corrected it, light no longer worked..

 

[ericmark]

It is common when a standard ceiling rose is replaced for the loop wires to be put in a connector or even worse just twisted together and hidden behind the plaster. Then the next person may be completely unaware the loop wires even exist. But while moving the switch line and neutral they can disturb the loop line wires sometimes even plastered into the ceiling where repairs have been made and so lose supply to next lamp in daisy chain.

 

[00775]

yes i see what you're saying but all wires seem visible (it's a wall light, not ceiling light) ie nothing plastered away. they are all sitting in a plastic casing, unless there is something behind the casing?!. i think i must have disturbed something though and as i can't fix it, i will just call someone out..

is it possible that the problem caused by the electrician in the bathroom with the fan could have now affected my upstairs lights?

thanks for your help ericmark..it's a bit of a minefield! i think i need to get someone out anyway, just to check the last guy's work if nothing else!

 

[ban-all-sheds]

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.

N is at 0v wo earth, not L.

The point PS was making is that if you reverse L&N to an appliance it will see absolutely no difference. For sure there are all sorts of other issues which get worse the further back up the line the reversal occurs, but at the appliance level, (e.g. plugging in an IEC 60320-C7) there's no effect.

If you were really perverse I'm sure you could design a Class I appliance which stopped working or even went bang if the wrong conductor was at ±325v wo earth, but I've never heard of anyone doing that...