Reverse Polarity Mains Socket -- How Dangerous?

OK - the extra info helps.

I think you have an older TT installation. This means because your supply comes in on overhead wires, the earth is provided by you - the customer, and not by the electricity company (who only supply live and neutral).

Because customer supplied earths are considered less reliable, slightly more elaborate protection is provided at the consumer unit (hence your

2 ELCB's).

However ELCB's are the older way of doing it. Now they use RCD's - which are considered more reliable. (Basically an RCD will work correctly regardless of how good or bad your earth is, whilst an ELCB may not).

One option available is a replacement consumer unit with appropriate RCD's (TT installations usually have 2, one less sensitive one for the whole house, followed by a second more sensitive one just for the ring mains).

Another option is to have the TT supply upgraded to TN-C-S (also known as PME) as well as a simpler single RCD consumer unit (IMO this is the better option).

Either way I would still have your installation checked out by a professional, and your earth tested (check they are able to do this).

Regarding the dodgy socket - it could have all 3 wires transposed (live is connected to neutral, earth to live, and neutral to earth). This would explain why very low powered devices could be plugged in and work ok (because they usually don't pass enough current to trip the ELCB), but anything larger does.

Bear in mind some plug-in socket testers are unable to detect earth/neutral transposition.

Reply to
dom
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It could still be a fault on that socket - and the devices are performing correctly.

For instance, the microwave could just happened to have been switched on just as the device on the faulty socket decided to draw more power (e.g. a phone charger cycling).

A low power device may just be apparently working ok, even though it's passing current between live and earth (because of faulty household wiring) - just not quite enough to trip the ELCB all the time.

However if always operating the microwave on a believed good socket causes a trip, then your explanation and not mine becomes the prime suspect.

Reply to
dom

On 26 Nov 2006 12:47:52 -0800 someone who may be " snipped-for-privacy@gglz.com" wrote this:-

Then the socket tester would have indicated faults with most of the other sockets.

Reply to
David Hansen

On 27 Nov 2006 02:18:11 -0800 someone who may be "Andrew Thelwell" wrote this:-

Do these things look as if they are 30 years old, or more recent?

What do you mean by 'loop'?

Could you put a photograph of the above and the consumer unit on the web somewhere?

Notoriously unreliable gadgets, largely useless.

Reply to
David Hansen

Not if it was a spur.

(which is most likely for a badly wired add-on)

Reply to
dom

Hi, OP here again,

Thanks for the further feedback.

A few more responses:

1) I would doubt that the appliances in the spare room are faulty, to be honest. They are all very new items: an LCD TV, XBOX 360, amplifier, laptop... all new or nearly new (nothing older than 18 months). The socket in that room shows up reversed on my plug-in tester but apart from twice tripping the ELCB, everything works just fine.

2) The ELCBs look like they may be anything up to 30 years old -- they don't have a modern look to them, although I've tested them both and they work fine. I'll try to put up a photo online later. One controls the kitchen sockets and lights, while the other covers everything else in the house.

3) The microwave has tripped the kitchen ELCB once and once only when being turned ON. The 'reversed' spare room socket has (so far) caused two trips of the other ELCB - once when turning ON the switch (even though no appliance were actually in operation, although I guess the LCD TV and XBOX may draw power right away as they have 'stand by' type function, yes?). The other time it tripped, it was when I turned the socket OFF (after charging a battery in there for 24 hours+). Does this give more clues?

4) My plug-in mains tester does not detect earth-neutral transposition explicitly (it doesn't have it as an option)

Thanks,

Andy

snipped-for-privacy@gglz.com wrote:

Reply to
Andrew Thelwell

Yup...

In fact at that age you may find that there is no dedicated earth at all. Our house was wired in a similar way once, and the only earth was provided by the gas pipe. It may be worth checking where the earth wires from the CU (or ELCB if they are external to the CU) go to.

They can however be sensitized by leakage from a faulty applicance such that they are prompted to trip when a non faulty appliance with a small legitimate earth leakage (such as a bit of computer kit with RFI filter on the mains input) is connected.

With a ELCB the liklihood of a trip will also increase as the weather gets wetter, since this will tend to loawer the earth impedance of whatever you are using as an earth.

Yup... I am supprised that somone doing this type of job is trusting his life to one of those toy screwdrivers!

Andrew, what sort of wiring is there in the house? Modern PVC clad stuff or old rubber or rubber/fabric coated stuff?

I would tend to agree - the socket polarity fault sounds like it is not directly related to the tripping problem.

Note that the faulty appliance could be a fixed one like an immersion heater, electric shower, cooker element etc - i.e. things that came with the new house rather than one brought with.

(things with heating elements are prime candidates for high earth leakage)

Reply to
John Rumm

On 27 Nov 2006 06:36:48 -0800 someone who may be "Andrew Thelwell" wrote this:-

I'll be interested in the photographs. My initial thought was that they might be voltage operated devices, but it would be difficult to install two in one installation.

AFAIAA none of them do, because it would be difficult to do in a cheap bit of equipment.

Reply to
David Hansen

On Mon, 27 Nov 2006 15:41:03 +0000 someone who may be John Rumm wrote this:-

Presumably that is the level of training they get now.

Reply to
David Hansen

Neon screwdrivers are notoriously unreliable. However, with an overhead supply it's quite common to have a few volts from neutral to true earth, and that's what his screwdriver was seeing.

Reply to
Dave Plowman (News)

No, an elcb doesnt care how bad the earth impedance is, it will still work. And even old ELCBs are still orders of magnitude more reliable than rcds.

this wont solve anything

nor will this. A single RCD CU is th worst possible optoin in fact, and will cause the OP even more trouble.

earth impedance testing is an easy diy job, and is cheap to do. Not sure that it would be especially useful though.

N/E swaps would fit the symptoms, so would leaky appliances, and less likely one or 2 other possible faults. I think time for some house-wide testing, once the socket polarity swaps are sorted. Such testing is simple to diy.

1 I'd open the Cu and visually check there are no L/N or N/E swaps. 2 I'd check all the sockets for the same thing. 3 I'd insulation test all appliances with a multimeter 4 I'd insulation test fixed items like immersion heater, oven, shower.

If by then the problems havent been sorted I'd be fairly surprised. NB if the wiring is rubber, dont do 1 or 2, as sisturbing rubber wiring tends to cause major problems.

NT

Reply to
meow2222

Theres something more going on if that skt trips the elcb. Fix the socket polarity swap first, test your appliances for earth leakage. Either a leaky appliance (you have a lot of faith in new goods), a miswired exntesion lead or a n/e swap.

photo might tell us if theyre i or v operated, which would help.

yes, but nothing definitive.

NT

Reply to
meow2222

ELCB's frequently trip in error conditions outside the house, over which the householder has no control, such as overlapping earth resistance areas, and other causes of external ground currents (lightning being a common one, and someone else's earth leakage being another). This is why they have a bad reputation for false trips.

Reply to
Andrew Gabriel

The message from snipped-for-privacy@care2.com contains these words:

Provided it's lower than about 8k ohms!

Reply to
Guy King

Hello again all,

I've put up a photo of our consumer unit and a close-up of one of the ELCB's.

They can be found here:

formatting link
are high-res photos

Your help is appreciated!

Thanks!

Andy

Andrew Gabriel wrote:

Reply to
Andrew Thelwell

They are RCD's, not [voltage operated] ELCB's. RCD's were originally called current operated ELCB's (14th Ed Regs), but that name didn't stick.

Reply to
Andrew Gabriel

Come to think of it, the other give-away is that you can't have multiple [voltage operated] ELCB's on one installation.

Reply to
Andrew Gabriel

The message from "Andrew Thelwell" contains these words:

This house of your - the roof timbers haven't got "The Ark" burnt into them somwhere, have they?

Reply to
Guy King

...and this changes everything. Any appliance you plug in that trips it is liable to be leaky, but no guarantee its that one. I had assumed they were voltage operated elcbs. Get used to trips and having to throw out appliances that work ok.

NT

Reply to
meow2222

You jest? We used to use them on 'The Bill' camera setup when running from mains, (obviously). If the camera touched anything vaguely conductive it would trip. Even just setting it down on the ground.

Reply to
Dave Plowman (News)

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