Reverse Polarity

[housewife59]

Apologies for intruding on your website - I am NOT an electician!! I would like some advice - a couple of weeks ago a MeterPlus employee came to fit a new meter in my house - he spotted a fault - said it was reverse polarity - the whole house was affected & told me to get an electrician to sort the problem. To cut a long story sort the problem was identified yesterday as aNEDL problem arising from underground cabling in the village 5 years ago. Basically I was told that the tails to the box on the outside of my house had been wrongly connected causing the reverse polarity. I would like to know what if any risks this has posed to me & my family over the last 5 years but more worryingly if the instalation was wrong to my property what about the rest of the village? Any comments or observations would be most welcome

 

[pushrod]

Have you an example please ?

I still cant understand why polarity of a singe phase A.C. supply can make any diffrence at all to the operation of an appliance.

To be fair to Des it was not him who said that appliances are functionally polarity dependent - he has just said there might be a few appliances that are sensitive. AFAIK (which might not be much) it is appliances/machines that are receiving a DC supply that would be polarity dependent. For something like an AC series/universal motor to run backwards you would have to reverse connections to one of either the field, or the armature connections - but this is not an eg of polarity reversal, more a case of rewiring.

 

[Golden_Boy]

I think to put it n very basic terms for you a normal supply the red/brown cable is the live one and has all the switchs and controls on that cable. The black/blue cable is the return path and when you switch something off the black/blue should be dead and totally safe to touch.

With reverse polarity the black/blue becomes live and then constitutes a danger plus you will find that if you are using an appliance that is polarity dependant it would go backwards.

Hope that helps to explain it better to you


Chris

Thats what had me

Cheers guys...

 

[Des 56]

Have you an example please ?

I still cant understand why polarity of a singe phase A.C. supply can make any diffrence at all to the operation of an appliance.

I am not making a case for reverse polarity causing machines or appliances to have damage, but would not dismiss it outright
I dont have enough knowlege of electronics to make a statement that it wouldn't

If you were to describe a simple mains powered smoke alarm as an appliance not an accessory,then applied reverse polarity,the detector would give up the ghost instantly,

At a guess, grounded electronic controls on washers and the like could have heat generated into the control board with continuous connection of components when the supply is reversed and damage could occur

 

[davelerave]

reverse polarity on a mains smoke alarm-i'll be amazed if it doesn't work properly

 

[Des 56]

Still trying to get my head around this a bit - isn't what you are describing above is if the reverse has taken place probably some distance from the installation and you have ended up with the earthing connected to the live. But then as you said all metal work would belive and the real live would effectively be linked directly to earth via the water pipes - wouldn't that take out the local substation? (as the main fuse would be in the neutral) Difficult to imagine how that could go undetected for such a long time.

Isn't it more likely that the polarity reverse took place at the installation with the neutral and earth being correctly linked but then fed to the " live" wires of the installation and the real live being fed to the neutral? If it is like this you could imagine it going undetected for a long as it is only in an earth fault situation that you would become aware of it as all the protective devices of the installation would be effectively in the neutral (so the fault path would be neutral of the installation to cpc bypassing the protective devices - still very dangerous!)

Non metalic supply services ?

 

[Des 56]

reverse polarity on a mains smoke alarm-i'll be amazed if it doesn't work properly

Personal experience made me make that statemnt

 

[davelerave]

Personal experience made me make that statemnt

reverse polarity and 'interconnect' propely wired-causes malfunction ? that's surprising to me anyway


i've had experience of getting the interconnect wiring wrong -but that's a separate issue

 

[Des 56]

http://www.safelincs.co.uk/tech/ke-23hi-installers.pdf


Found something that warns of reverse polarity for alarms
Scroll down to page 5

 

[davelerave]

say's it at the botom of page alright-reverse polarity

thought it was only mixing the interconnect that caused a 'blowout'


that was a trick question anyway

the interconnect is ELV isn't it?

 

[pushrod]

Non metalic supply services ?

Good answer , but from what housewife subsequently said i'm guessing i'm correct

 

[Golden_Boy]

I am not making a case for reverse polarity causing machines or appliances to have damage, but would not dismiss it outright
I dont have enough knowlege of electronics to make a statement that it wouldn't

If you were to describe a simple mains powered smoke alarm as an appliance not an accessory,then applied reverse polarity,the detector would give up the ghost instantly,

At a guess, grounded electronic controls on washers and the like could have heat generated into the control board with continuous connection of components when the supply is reversed and damage could occur

There are no "grounded" connections thats the whole point of insulation !!
Yes but thats DC not AC.... I seem to have opened a can of worms here and wish I had kept my mouth shut...

Its only that others had mentioned this and as far as I know there is not ANY AC , stand alone , domestic appliance that will not work when connected either way round to a single phse AC supply. Thats why the OP did not know about the reversal issue !!!

 

[Risteard]

Yes but thats DC not AC.... I seem to have opened a can of worms here and wish I had kept my mouth shut...

Its only that others had mentioned this and as far as I know there is not ANY AC , stand alone , domestic appliance that will not work when connected either way round to a single phse AC supply.

In an AC supply incorrect polarity means that the supply won't disconnect in the event of a fault, or where switched off etc.

 

[Golden_Boy]

In an AC supply incorrect polarity means that the supply won't disconnect in the event of a fault, or where switched off etc.

I'm not disputing that, What I am saying is that there are no AC appliances that will not run correctly ( safety appart ) from an AC supply no matter how it is connected.. Unless someone knows better? Otherwise how does an appliance containg a mains transformer ( wound NOT switch mode) work at all?

 

[ezzzekiel]

sky box is polarity sensitive

 

[Mark42]

I'm not disputing that, What I am saying is that there are no AC appliances that will not run correctly ( safety appart ) from an AC supply no matter how it is connected.. Unless someone knows better? Otherwise how does an appliance containg a mains transformer ( wound NOT switch mode) work at all?

I agree.

Think of it from a single-phase appliance’s ‘point of view’: All it sees is a waveform swinging one way then the other about ground potential. Or you can think of it as the electricity being pushed towards you, then pulled back, 50 times a second. (Yeah, OK, ignore the quantum stuff…)

A reverse of the AC supply ‘polarity’ (polarity is a totally meaningless concept with single-phase AC anyway – except at any particular time instant) can not possibly be ‘perceived’ by any appliance.

I think the word polarity is confusing when applied to AC circuits. It only has any meaning in polyphase systems where I suppose it’s a kind of shorthand for relative phase angles, which of course do matter, since they affect (are proportional to) the RMS voltage between phases, or between any phase and ground.

What we’re really talking about in practical single-phase systems is which colour wire we choose to be at ground potential, and which wire to have the energy relative to this bloody great lump of rock we all have to stand on.

I think this is right – feel free to shout abuse if I’m wrong, since I’m an explosives engineer, not an electrician. I can take it

Oh, and Housewife: Your story is an outrage. You were potentially in great danger. I suggest a report to Private Eye magazine.

Ps: Sorry, stuff about vacuum cleaners blowing instead of sucking is pure fantasy. We gave up any idea of DC distribution years ago! (And three-phase vacuum cleaners are rare in most homes )