crossed neutrals

SC024

Maybe a silly question but say for example you had a crossed live/neutral on a lighting circuit /Could would this cause your esb meter to run up a large bill?

2011

SC024 wrote: »

Maybe a silly question but say for example you had a crossed live/neutral on a lighting circuit /Could would this cause your esb meter to run up a large bill?

"Crossed" as in connected to each other?

No.
You are describing a "short circuit". This generally causes a flash and a bang and should trip the upstream MCB.

eeguy

If the wires are touching then no.

However if "something" is bridging the wires then possibly, on the condition that 1, the something is not earthed, 2 the something has a resistance such that the current flowing through it is less that the breaker rating for that particular circuit and 3 the something is capable of dissipating the power dropped across it.

Very unlikely and I'm open to correction on any of these points.

meercat

think op means reversed polarity,this shouldnt have any bearing on meter reading(needs to be checked though)

AC isn't polarised. I'd suspect the wiring colour code unconventional.

SC024

Thank guys

eeguy

Sir Liamalot wrote: »

AC isn't polarised. I'd suspect the wiring colour code unconventional.

Not universally true. You can get away with it in basic devices,, but beyond that you'd want to make sure you have your wiring done correctly.

Bruthal

eeguy wrote: »

Not universally true. You can get away with it in basic devices,, but beyond that you'd want to make sure you have your wiring done correctly.

What 2 wire AC devices would be polarity sensitive, since polarity doesnt really exist in a 2 wire AC supply?

eeguy

Bruthal wrote: »

What 2 wire AC devices would be polarity sensitive, since polarity doesnt really exist in a 2 wire AC supply?

Audio stuff and some mains filtering devices and non isolated power supplies can be sensitive depending on design. It's also a safety issue. Fuses are usually on the live and reversing polarity can bypass the fuse.

Irish Steve

eeguy wrote: »

Audio stuff and some mains filtering devices and non isolated power supplies can be sensitive depending on design. It's also a safety issue. Fuses are usually on the live and reversing polarity can bypass the fuse.

Oh Dear.

The Fuse is NOT bypassed, but in some circumstances, if the fuse fails and is in the neutral line, there is the potential for 240V to be present on components of the device, and in some fault situations, depending on external protection, current could flow to earth, which is not desirable, and could indeed present a safety hazard.

eeguy

Irish Steve wrote: »

Oh Dear.

The Fuse is NOT bypassed, but in some circumstances, if the fuse fails and is in the neutral line, there is the potential for 240V to be present on components of the device, and in some fault situations, depending on external protection, current could flow to earth, which is not desirable, and could indeed present a safety hazard.

Yep that's what I meant.

Bruthal

eeguy wrote: »

Audio stuff and some mains filtering devices and non isolated power supplies can be sensitive depending on design.

With only 2 wires though, there is not much reference to anything. Audio stuff is likely to have an isolating supply.

It's also a safety issue. Fuses are usually on the live and reversing polarity can bypass the fuse.

I`m more talking about in terms of operation. Other countries appliance plugs can be plugged in either way around. Connect a neutralized house up with L and N the wrong way around into the esb fuse unit and its not going to be great though.

Risteard81

Presumably by crossed neutrals he means a borrowed neutral, i.e. a neutral taken from a different circuit than the phase conductor.

Actually, rereading I'm not 100% certain that this is what was meant - it's not entirely clear.

Risteard81

Presumably by crossed neutrals he means a borrowed neutral, i.e. a neutral taken from a different circuit than the phase conductor.

Actually, rereading I'm not 100% certain that this is what was meant - it's not entirely clear.

eeguy

Bruthal wrote: »

I`m more talking about in terms of operation. Other countries appliance plugs can be plugged in either way around. Connect a neutralized house up with L and N the wrong way around into the esb fuse unit and its not going to be great though.

Yep buy they use double pole fusing, lower amp MCBs and different domestic wiring. My point is that it's not good practice to simply say that polarity doesnt matter.

Bruthal

Risteard81 wrote: »

Presumably by crossed neutrals he means a borrowed neutral, i.e. a neutral taken from a different circuit than the phase conductor.

Actually, rereading I'm not 100% certain that this is what was meant - it's not entirely clear.

L and N swapped around Id say they mean.

Bruthal

eeguy wrote: »

Yep buy they use double pole fusing, lower amp MCBs and different domestic wiring. My point is that it's not good practice to simply say that polarity doesnt matter.

Nobody said it doesnt matter though.

The plugs in continental appliances have no fuses.

Polarity does matter but AC doesn't have one (it reverses at 50Hz) . Wiring convention matters and for these purposes (switching/protection) we say (in this country with single pole MCBs) that electricity comes in a live and returns the neutral. In reality the electrons are vibrating not flowing like a DC circuit that does have a polarity.
Yes there's a difference in potential WTE that is sensitive to some applications but lights are not one of these.

Steve

Polarity does matter in a TN-C country like ours.
The N phase is always going to be at or about earth potential and in older builds neutrals were starred and commoned all over the place.
Mixing a live potential on to this would cause all sorts of weird stuff to happen.

Bruthal

Steve wrote: »

Polarity does matter in a TN-C country like ours.
The N phase is always going to be at or about earth potential and in older builds neutrals were starred and commoned all over the place.
Mixing a live potential on to this would cause all sorts of weird stuff to happen.

True, but as was said, it has not been stated that it doesnt matter. More that polarity doesnt really exist in AC in the same sense as in DC. Plug in the tv, vacuum cleaner, drill, with L and N reversed, and they all still work the same.


Great minds, (or fools)

Bruthal wrote: »

Connect a neutralized house up with L and N the wrong way around into the esb fuse unit and its not going to be great though.

Lights and ESB meters aren't "AC polarity" sensitive devices.

If you're worried just turn the bulb around.

Bruthal

Sir Liamalot wrote: »

Lights and ESB meters aren't "AC polarity" sensitive devices.

If you're worried just turn the bulb around.

Well no, but you wouldnt want an esd land man/woman coming and connecting the supply cable in reverse at the fuse unit.

Also, on the older type disc meters, they will reverse if the supply and load are reversed, since the current direction at any instant on the phase is now opposite with reference to the current through the voltage detection part.

Agreed.
However then the bills would reduce not increase and you'd notice a supply fault fairly lively.

The new supply meter rollout in the UK was prompted by customers with backward spinners due to PV arrays.

Steve

The old disc meters couldn't do that, there was only one in / one out. Unless you reversed line and load, they would always measure.

One of my Kevin St lecturers many many years ago was ex ESB and he told stories of things people tried to do to 'fool' meters.

Bruthal

Sir Liamalot wrote: »

The new supply meter rollout in the UK was prompted by customers with backward spinners due to PV arrays.

That,s right yea. It should come along here in about 2150 id say.

Steve

Sir Liamalot wrote: »

The new supply meter rollout in the UK was prompted by customers with backward spinners due to PV arrays.

How did that work?

Just curios, I know it's illegal here.

Wouldn't have thought any PV source could generate enough to make a difference.

Bruthal

Steve wrote: »

How did that work?

Just curios, I know it's illegal here.

Wouldn't have thought any PV source could generate enough to make a difference.

Well if you have a 2kw output from home generation, and a load of 500 watts on in the house, its backwards meter time. So they install meters to properly measure the grid fed surplus.

Dunno exactly I never had one. I've just seen reports on other forums of people being unavailable as long as they could manage after reporting the fault when asked to facilitate engineers to "upgrade the meter".

PV will produce rated output under STC all you'd have to do is reduce the import/loads.

Steve

Bruthal wrote: »

Well if you have a 2kw output from home generation, and a load of 500 watts on in the house, its backwards meter time. So they install meters to properly measure the grid fed surplus.

You're right, sorry, I only ever looked at it in financial rather than electrical terms - It will always will be a nett loss due to cost of equipment vs what it you could possibly sell back to the grid (if it was legal) over its lifetime.

Bruthal

Steve wrote: »

You're right, sorry, I only ever looked at it in financial rather than electrical terms - It will always will be a nett loss due to cost of equipment vs what it you could possibly sell back to the grid (if it was legal) over its lifetime.

It would be interesting here, if ye did send the meter in reverse, the fraud squad would probably be out.

Steve

Yeah, jail time for sure.

Worse than importing garlic but not as bad as ripping off a country for 60 bill...