Polarity Reversing At Will

[securespark]

HISTORY:

Gas Engineer visits property: Polarity on boiler reversed.

Electrician visits: Polarity OK.

Gas Engineer visits: Polarity reversed.

Electrician visits: Polarity reversed. Calls DNO. DNO arrive, test, and Polarity OK.

HOW??

TT system with no rod, but evidence of tampering to cut-out & link to cutout. for earthing. Zs of 12.16 - earth connection coming from pipework. Ze 87.4.

 

[C&GStudent]

How can the polarity reverse itself? Is that even possible? I don't know.



Hmmm...

Maybe someone has been fiddling with it! Or a simple human error by one or both technicians.

I'm just thinking out loud, it will be interesting if one the pro's knows the answer.

 

[Mike4]

HISTORY:

Gas Engineer visits property: Polarity on boiler reversed.

Interesting. Is it just the boiler with the intermittent reversed polarity or is the rest of the circuit it is fed from reversing too? Are other circuits reversing? Is the whole house reversing?

What method is being used to test boiler polarity?

What make and model is the boiler?

Cheers, Mike

 

[Mike4]

Electrician visits: Polarity reversed. Calls DNO. DNO arrive, test, and Polarity OK.

I think we need to pin down the extent of the problem.

From the fact that the DNO was called in, are you saying polarity is reversing at the consumer unit too? If so, mentioning the boiler is a red herring!

Cheers, Mike

 

[Mike4]

How about this ammended scenario:

HISTORY:

Gas Engineer visits property: Engineer observes polarity on boiler appears to be reversed as brown is connected to N and blue is connected the L on the boiler terminals. Fails to note that BOTH ends of the flex are reversed, so boiler polarity is actually correct.

Electrician visits: Takes heating system isolator switch plate off and confirms polarity of supply into heating wiring centre is correct, having slightly misunderstood the problem being reported.

Gas Engineer visits: Sees connections on boiler terminals still wrong way around, and decides to correct the fault himself, swaps them over and unwittingly introduces actual revered polarity at the boiler.

Electrician visits: Tests boiler. Polarity reversed. He KNOWS the supply at the switch plate is correct because he tested it previously, so he calls DNO. DNO arrive, test at consumer unit, and find Polarity OK.

Or something along these lines. I think ONE person needs to be doing the testing, and not the gas engineer!

 

[sm1thson]

Hmm, a TT system, now i have no experience in this area (i am an electronics not electrics man), if the earthing back at the station wasnt clamping the neutrual to earth correctly then you wouldnt be able to identify phase and neutrual as such, so could something along these lines this be the start of some of the problems? (if it is the whole house thats playing up)

 

[JohnD]

Mike's history is presumably a guess, but I would be thinking about the different people testing at different points, using different kinds of instruments, or different methods to test.

I have a feeling that if all the people were present at the same time, watching each other, they would quickly start accusing each other of doing it "wrong" (i.e. differently).

It is not unknown for TT polarity to be wrong, but the DNO know that, and should have checked and spotted it when called in, including if the error was upstream of the house.

 

[Big_Spark]

I would hazard that a potential scenario could be as follows...

The incoming feed has been misconnected, perhaps at installation or at some later date.

Someone has noticed this and connected things up in such a way as to overcome this problem.

When the heating engineer installed the boiler, he connected it up correctly, assuming correct polarity. The boiler didn't work, so another, or perhaps the same, engineer came out to inspect, he spotted a crossed polarity and the electrician was called in.

The electrician does his test, finds that the problem is actually the supply so calls in the DNO.

The DNO send out an engineer, he spots that a simple mistake has been made, corrects it, and then states that the polarity is OK.

Now I am not saying this is what the situation, however I have seen a similar situation occur with a submain feed from one service head to a secondary one where the engineer doing the connecting up did it wrong!! (That was on a TN-S system though not TT.)

The problem with such situations is that we only have third or fourth party stories to base our thinking on, and perhaps some of the information has not been passed accurately from one engineeer to the other, and at the end of the day, if it is on the supply side, then it's the DNO's problem, but if you can confirm the supply is OK, then the spark has a headache sorting it out..and the client willprobably get a big bill too!!

 

[sm1thson]

i have another idea (again i dont claim to be right, its not a subject i know about just a guess!)

you said there is no earth so what are you measuring the voltage with respect to? metal pipework? if so could this happen:

applience with slight earth leak turned on elswhere: so there is a potential (but low current) on the pipes there fore voltage between phase and pipes low, but between neutrual and pipes is high!

applience turned off: no potential on the pipes there fore voltage between phase and pipes high, but between neutrual and pipes is low!

and the cycle continues!
any thoughts???

edit: just reread OP and saw that dispite the no rod there is a half decent earth through the pipes (and i dont understand the cutout terminoligy), still i liked my idea so i will leave it up, lol. edit- it may even be valid if there isnt contiuity in the earthing arrangements??

 

[toasty]

someone connected in an intermediate switch instead of a fused spur maybe???

When "on" polarity would be one way, when switched "off" it would be reversed..

Could it be that?

 

[toasty]

or failing my first idea.

Maybe the house owner disconnecting and reconnecting the meter (maybe in reverse) in an attempt to pay less for electricity?

 

[ricicle]

someone connected in an intermediate switch instead of a fused spur maybe???

When "on" polarity would be one way, when switched "off" it would be reversed..

Could it be that?

Surely a labotamised sparky could spot an intermediate instead of a switched fuse spur

 

[Lectrician]

Havn't read replies, but have seen a similar thing..

House fed by own pole mounted tranny. Neutral tie-down corrodes, which effectively gives an AC supply, with no real refference to earth, and hence, no polarity at all.

The HV guys will sort this - The trannies are their game.

Boilers are very fragile with polarity these days - the electronics become very unstable on a reversed polarity.






Had a plumber a few years ago go to a site we had wired - supply not yet connected. Y plan system was was wired by us, and supplied by an FCU.

Plumber opened FCU, and connected directly to a plugtop, and plugged into his extension lead, which was plugged into the site temp supply. System functioned, but boiler wouldn't fire.

Plumber tested at boiler, and set it had reverse polarity at it's terminals, and reversed them in the boiler to get it running.

He had a phone call, fairly ****ty, from site foreman.

On attending, we find no fault at all on our wiring.

Plumber turns up, all cocky etc etc.....


Turns out, after some testing, that the PLUMBERS extension lead, which HE made was wired with reverse polarity!

 

[securespark]

OK.

The gas guy checked polarity at boiler spur with a Martindale: REV

The spark checks polarity at boiler spur, socket and origin with an Alphatek: OK

Different gas engineer checks boiler spur with Martindale & Alphatek: REV

Different spark checks boiler, socket & origin with Martindale & Alphatek: REV.

DNO called: They check it at Origin: OK

The house is part of a terrace fed by an overhead PVC TT cable from a pole a way away. There are 6 houses before this one.

Please note that two different gas guys & two different sparks have checked things, so it is not down to equipment.

There is a switched spur, not an INT switch!!

The DNO guy did not do anything other than check polarity. He did not alter anything.

The sparks commented that everything they tested was REV, not just one circuit.

The gas guys were quizzed by myself. They have not altered anything. In fact, they are forbidden by co. policy to even touch an appliance once they have discovered a fault such as RP.

I went the other day. I checked polarity at the boiler: OK At a socket: OK At a lighting point: OK At the origin: OK

I checked the tails were the right way round, right through back to the cut-out. I even checked the RCD (on split board) was plumbed in OK. I even checked there were no signs of tampering to meter etc. The only sign of tampering was the introduction of a 16mm2 conductor into the cut-out, which is obviously not PME'd, as evidenced by the huge Ze.

I rang a technical manager who said he had come across this once in 30 years: A GenSet used on TT supply was causing Polarity Reversal. Don't know how though....

 

[RF Lighting]

I'm off to the pub to think about this one.

I'll get back to you