Live neutral reverse detected. Help please! RCD wont reset

[Fishmilk]

Hi all, i have just moved into a old house and have just fitted a new dishwasher using a extension lead connected on the RCD side of the consumer unit as all sockets are. When using the dishwasher the RCD tripped, so straight away i assumed the socket was at fault so i used a different socket that was there when i moved in. Same again the RCD tripped. I have tried different extensions all exceeding the ratings needed by the dishwasher, many different sockets but still it tripped. I then used a living room socket and all seemed ok, until i plugged the hoover in the kitchen socket and again the RCD tripped but now wouldnt reset. I unplugged all appliances and went to the consumer unit, i then turned all mcb's on the rcd side of the board off and still the rcd wont reset. I have changed the downstairs sockets and they are now not on the rcd side of the board so all sockets and appliances now work. I have since brought a socket tester as i thought this would be handy and on every socket in the house it detects live neutral reverse. Again i checked in the consumer unit and all mcbs appear to be installed correctly but i have noticed that the tails that enter the house seem reversed, the red wire goes to the main switch on the side marked 'N' which is neutral and the black tail goes next to it. Now i have checked everywhere and i am a auto electrician but principles like this are pretty similar. If the live and neutal are reversed but my appliances all work then could this have been the cause of my rcd tripping and was triggered by the installation of the dishwasher? Or would live neutal being reversed not allow anything to work? I understand the operation of an rcd is to measure earth leakage by the differential between live and neutral so i suspec this to be the cause but any help or problems with wylex rcds or live neutal help is much appreciated thanks.

[Allan Mac]

and all mcbs appear to be installed

this is a bad situation because if you have an earth to neutral short,it will infact be a live to earth fault with no MCB in circuit, ie a huge fire risk. Get this fixed asap. If your RCD still trips make sure the neutral of the socket you installed is connected to the RCD side of the CU and not the non RCD side. (same goes for all other neutral connections , make sure they go to the correct side of the box. GOOD LUCK. Allan.

[pete]

I had a similar experience when a chest freezer was giving people a belt. It turned out to be a problem with the 2.5mm cable behind a tile of all places. For whatever reason a piece of the cable had melted and the live shorted to earth. The freezer still worked. I have never seen anything like it before as nothing tripped. Try and isolate lengths or sections of the cable and test them.

[meow2222]

L/N reversal means the only effective fuse between every appliance and fireworks or electric shock is the main 100A incomer fuse. This isnt good.

Sounds like you may have found the problem. To correct it you'd need to pull the main 100A supply fuse, which is unswitched, and if old enough may not be too well insulated. You'd need to not make mistakes with that.

The rcd trip is a separate matter, I'd sort the L/N issue first, thats a real issue whereas the rcd one is minor.

NT

[John Rumm]

It sounds like you have a faulty dishwasher. Items containing electrical water heaters are prone to high earth leakage due to the nature of the heater construction.

It is possible you also have a faulty RCD, however just turning off the MCBs is not enough of a test (because the neutral for each circuit will still be connected).

What happens if you turn off all the MCBs (i.e. both RCD and non RCD side)?

What type of earthing arrangement do you have?

refer to the following if you are unsure:

failing that post a photo of the inside of the CU and the head end of your incoming cable somewhere where we can see it and we may be able to tell)

Did you remember to also move the neutrals for each of the circuits to the non RCD busbar?

I would suggest that this "remedy" even if it works should only be considderd a temporary fix, since you qould be far better off finding and curing the actual fault.

You need to establish where the reverse occurs. A test with a multimeter starting at the incoming switch of the CU would be a good start. If this is wrong at the input of the CU then this needs fixing ASAP.

Appliances will still work with reversed connections. That alone would not cause a RCD trip either. However we could use more information here.

The RCD measures the inbalance in current flow between live and neutral

- i.e. what goes it ought to come out. If it does not then there is an alternative return path somewhere that there should not be.

[Fishmilk]

It sounds like you have a faulty dishwasher. Items containing electrical water heaters are prone to high earth leakage due to the nature of the

heater construction.

The dishwasher cant be the cause of the fault as when the extension lead it is connected to is unplugged from any socket the rcd still trips and will not reset, Could the live and neutral being reversed be the cause of the rcd trip? What tests can i do with a multi meter? will i have to diconnect each circuit both ends to do the isolation tests or doesnt it matter?

[The Medway Handyman]

Did you have a survey on the property before moving in? If so, this should have been spotted - could you have a claim?

[Andy Wade]

A normal survey / housebuyer's report etc. normally excludes electrical and mechanical services, certainly to that level of detail. Caveat emptor applies, or rather appears not to have been applied in this case.

I would recommend a full PIR on the electrical installation as who knows what other dangers may be lurking.

[John Rumm]

(sorry if this shows up as a duplicate post - I started a reply and got distracted - then could not later find the one I had started, so I may have posted it by accident!)

From your description, that is not how the problem started out though. You could now have a different / additional problem, but that does not exclude the dishwasher. I am not sure why you came to the conclusion that a RCD trip would point toward a faulty socket... especially after you have tried several.

It seems unlikely.

Have you tried resetting the RCD while *all* MCBs are turned off?

What changes have you made in the CU since starting to investigate the problem?

Well you could start with working out where the polarity change is happening, by testing at various points in the circuit starting with the CU incomer. (use an AC volts range of 250V or higher)

Do a visual inspection to make sure that all circuits that are fed from a RCD protected MCB, also have a neutral returning to the RCD protected neutral bus bar. Check the non protected side in the same way.

With the power off, and each of the wires for a circuit disconnected in the CU, and everything unplugged from the circuit (and things connected via fused connection units switched off), you could test the resistance between each of the conductors (there ought to be infinite resistance (i.e open circuit) even on the highest range the multimeter supports.

For ring circuits you can measure the "round trip" resistance between both lives, neutrals, and earths to see that the ring is connected end to end, that the round trip resistance for Neutral and Live is approx the same, and a bit lower than that for the earth wires (the wire is a bit thinner).

If none of that reveals any obvious problem then where you go next will depend on how confident you feel in tracing through these problems, and what test equipment you have available. You may find that is a suitable point to call in an electrician to produce a Periodic Inspection Report for the property.

Google this group on RCD tripping problems - this comes up quite frequently and much detailed explanation of tracing the cause of problems has been posted.

[Peter Lynch]

Is this really much of a problem? On the continent, e.g. in spain, plugs are not fused and can be inserted into a mains socket either way up - making it impossible to differentiate L and N.

Anyone know how other countries deal with this "problem"?

Pete

[Dave Fawthrop]

|On 17 Dec 2006 12:28:55 -0800, Allan Mac wrote: |> and all mcbs appear to be installed |>> correctly but i have noticed that the tails that enter the house seem |>> reversed, the red wire goes to the main switch on the side marked 'N' |>> which is neutral and the black tail goes next to it. Now i have checked |>>

|>

|> HI, |>

|> this is a bad situation because if you have an earth to neutral |> short,it will infact be a live to earth fault with no MCB in circuit, |> ie a huge fire risk. Get this fixed asap. If your RCD still trips make |> sure the neutral of the socket you installed is connected to the RCD |> side of the CU and not the non RCD side. (same goes for all other |> neutral connections , make sure they go to the correct side of the box. |> GOOD LUCK. |> Allan. |>

| |Is this really much of a problem? On the continent, e.g. in spain, |plugs are not fused and can be inserted into a mains socket either way |up - making it impossible to differentiate L and N. | |Anyone know how other countries deal with this "problem"?

People die from electric shock.

[meow2222]

One might, but is it really worth a claim for the sake of half an hours work?

NT

[Andy Wade]

Yes it is. I think you might be confusing or conflating two issues.

Yes, but the wiring up as far as the sockets in those countries does have defined polarity such that the circuit fuses or circuit breakers are in the phase ("live") conductors. The fixed wiring can cope with faults (L to N, or L to E), whether in the fixed installation or in an appliance. The fact that plugs & sockets allow appliances to be connected "either way round" isn't of any consequence in this discussion.

OTOH what the OP has is a polarity reversal at the installation origin, such that all the fixed wiring is only protected by the 100 A supplier's main fuse. Such "protection" will be ineffective against L-E faults (shorts) on all but the largest circuit cables.

[Peter Lynch]

clarity! thanks for an intelligent and helpful post

Pete

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Dave Fawthrop saying something like:

They die from breathing for too long, too.

[John Rumm]

Typically by installing loads of low current rated circuits where the circuit protective device is sized such that it will protect the flex of any appliance plugged into it. Since the fuse is not in the plug, it does not matter if the plug is reversed[1] - the fuse is still in the phase.

So all in all you tend to get loads of circuits, and less flexibility for general purpose power distribution.

[1] although if the appliance only has a single pole switch there is the possibility that the bulk of the appliance is left "live" when switched off.

[bob watkinson]

Why? Didn't you think the RCD might be doing its job? IE protecting you from earth leakage in your dishwasher.

L N reversal is another mater and is vital you get that fixed pronto. Why? replace a lamp with the light switched off, in your house the fitting can still kill you.