Reverse polarity points

[Derek Uzzell]

rupert123 - 2013-12-08 10:20 PM

 

It may be practical to waterproof a reverse polarity lead by why would you bother, throw it away. While I would agree it is not bad practice to test a mains hook up socket it is a waste of time.

 

I know this may go against the grain, but I suggest you re-read this thread from the beginning.

 

At the outset spospe mentioned that he had discovered that the mains-powered Airlectric unit in his Auto-Sleepers Duetto's Eberspacher heating system will not function if the polarity of the hook-up supply is reversed.

 

How he found this out and rectified the problem was, having realised that the heater wasn't working on mains electricity, he tested the power-supply, found that the polarity was reversed and used his "home-made reversed connecting lead to re-reverse the polarity" causing the heater to operate as one might anticipate it should.

 

For spospe to be able to identify the cause of the heater problem and side-step it, he needed a) to be aware of the potential for a hook-up supply's polarity to be reversed, b) to be able to test a hook-up supply for reverse-polarity and c) to have a means to 're-reverse' a supply having reverse-polarity.

 

Spospe has said that (very sensibly) he won't be playing about with his heater to try to get it to run on mains power from a reverse-polarity supply. This implies that, if and when he encounters a reverse-polarity supply, he must use a 're-reversing' adapter to permit his heater to function. And, to allow him to use such an adapter, he will necessarily have to carry one in his motorhome. Would you suggest to spospe that he should throw away his adapter (and consequently not have mains-powered heating) and that it's "a waste of time" for him to test mains hook-up supplies?

 

You aren't talking to 'newbies' here, babe, but anyone new to motorcaravanning would be better taking note of spospe's comment "I am 69, if I did not as a matter of routine test all electrical circuits before touching them, I would not be 69", than to your dismissive advice. Even if you are "a qualified electrical engineer", that doesn't make you infallible or omniscient, and it very definitely does not make you logical.

[spospe]

rupert123 - 2013-12-08 10:20 PM

 

While I would agree it is not bad practice to test a mains hook up socket it is a waste of time.

 

 

Is this not rather like saying, "While I would agree it is not bad practice to look both ways before crossing the road, it is a waste of time?"

[rupert123]

spospe - 2013-12-09 9:09 AM

 

rupert123 - 2013-12-08 10:20 PM

 

While I would agree it is not bad practice to test a mains hook up socket it is a waste of time.

 

 

Is this not rather like saying, "While I would agree it is not bad practice to look both ways before crossing the road, it is a waste of time?"

Not at all. Testing a mains connection for reverse polarity is not bad practice but why bother when the result does not matter. However I will say no more on the subject and leave it to the experts on everything like Derek to hand out advice about stuff they plainly know nothing about, other than what they have looked up on the internet.

[Brambles]

What concerns me is most think the heater should run with reverse polarity, so to me this may indicate there is a fault somwhere and this fault could manifest into a more serious and possibly dangerous fault. I would want to know if it does not work by design or is indeed a fault and what that fault is.

[pepe63xnotuse]

This is a "non-confrontational" query from a curious MH user, who has with VERY little in the way of electrical knowledge... ;-)

 

So..If reversed polarity in a MH is a dangerous thing, then why is that it isn't mandatory for some form of "polarity switching" device to be fitted as OE..?

(eg..You plug in/hook-up and if RP is detected a buzzer sounds and nothing will work until the switch has been selected..? Either that or something that "auto-corrects".. ?)

 

As it is, if RC is a present(and a danger?), then surely just relying on £2.99 testers...and some homemade patch leads(..that, let's face it, in many cases have only been put together by some unqualified, fumbled thumbed DIYer),doesn't seem a very satisfactory way of going about things... :-S

 

Having said that if someone IS going to start stripping down their electrical appliances and poking about , whilst it is still plugged in, then as well as the seeking out the "Ladybird" or " i Spy book of common sense", I'd suggest they also read up on Darwin! (lol)

[Brambles]

pepe63 - 2013-12-11 4:20 PM

 

This is a "non-confrontational" query from a curious MH user, who has with VERY little in the way of electrical knowledge... ;-)

 

Better understanding than I think you let on. You reverse confrontationalist you.

 

So..If reversed polarity in a MH is a dangerous thing, then why is that it isn't mandatory for some form of "polarity switching" device to be fitted as OE..?

Eggs act lay. There is of course your RCB device will will protect you if there is say Earth and live swapped. I was involved in setting up a production line once and the Chairman of company claimed to be qualified and wired up the benches....shame he had the earth and live swapped in quite a few socket outlets. I got the sack because of the rude abuse I gave him over that one. Never could work out why the RCB never tripped when I got a belt from equipment. Probably wired wrong as well. I actually think I was sacked because I told his wife he was a stupid Barsteward...she took his side and not mine..I was a naive 23 year old and never expected that.

 

(eg..You plug in/hook-up and if RP is detected a buzzer sounds and nothing will work until the switch has been selected..? Either that or something that "auto-corrects".. ?)

 

I thought we had agreed Reverse polarity was not an issue so why even discuss. But I get your point.

Eggs act lay again, they do not fit one do they and would if needed.

 

As it is, if RC is a present(and a danger?), then surely just relying on £2.99 testers...and some homemade patch leads(..that, let's face it, in many cases have only been put together by some unqualified, fumbled thumbed DIYer),doesn't seem a very satisfactory way of going about things... :-S

 

Maybe we need to regulate the supply of Reverse leads and make it illegal to use a home made one.

After all they become pat of your installation and unless quaified and registered you should not be playing with electrical installations. I know, lets just forget reversed leads as not required.

Any eggs left, feeling a bit peckish....nice with a mayonaise and curry sauce.

 

Having said that if someone IS going to start stripping down their electrical appliances and poking about , whilst it is still plugged in, then as well as the seeking out the "Ladybird" or " i Spy book of common sense", I'd suggest they also read up on Darwin! (lol)

 

Let them play, if they electrocute themselves they will not do it again. So in response..eggs act lay, who in their right mind would be so stooopid. How else are they going to fault find it without a meter to find what is wrong. Fingers make a great voltage sensor for fault tracing.

 

 

[pepe63xnotuse]

Brambles - 2013-12-11 5:14 PM

 

pepe63 - 2013-12-11 4:20 PM

 

This is a "non-confrontational" query from a curious MH user, who has VERY little in the way of electrical knowledge... ;-)

 

Better understanding than I think you let on. You reverse confrontationalist you.

 

 

(lol) ...Reading it back, edited like that, it does appear as if I was having a bit of a pop..but that wasn't really my intention.

 

(well...not until the "Darwin" paragraph anyway.. :D)

 

(..and I've only just realised that for some strange reason I had typed "RC", instead of "RP" ?? :$)..

 

 

[Derek Uzzell]

This 2007 forum thread deals with reverse polarity in some detail:

 

http://www.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Polarity-Tester-Reverser/8669/

 

A Mains Polarity Changeover Switch is mentioned and these are still marketed:

 

http://www.the12voltshop.co.uk/Shop/mains-polarity-changeover-switch-nov-30600-.html

 

I haven't looked at early forum discussions for a while, but it's interesting to see how polite people were then (Well, most of the time!)

 

 

 

 

 

[Gram]

In the interest of scientific discovery and human endeavour I have applied reverse polarity mains to my Symbol and tried the Eberspacher heating system.

 

The heating system comprises an Airtronic diesel heater and an Airlectric mains electric duct heater.

 

In normal circumstances the system will sense whether or not mains is connected. If it is, the Airlectric will come into operation and heat the interiior of the vehicle. If mains is not connected then the Airtronic diesel heater will come into operation.

 

With reverse polarity mains applied, the system fails to recognise the existence of mains power and the diesel heater operates.

 

This supports point 1) of spospe's original posting.

 

G

[Brambles]

Therefore we can probbaly conclude they are detecting the presence of mains by looking at the potential between the 'live' connection and earth rather then 'live' to 'neutral'.

They must have a reason for doing this, one I have not fathomed out yet but then have not really given it much thought. Hmmmm!

[spospe]

Thanks to Gram for his confirmation of point number 1 of my report.

 

My main reason for mentioning this phenomenon was to say that this was the very first occasion that I had come across since 1977 (when I started caravan / motorvan use) where reversed polarity has had an obvious effect on the functioning of any installed apparatus.

 

No, I am not investigating why this is so. The installation of mains electrical services in the UK is based on the correct wiring of Live, Neutral and Earth and I am not even slightly interested in investigating why the system will not work when it is incorrectly wired. We have a standard and this standard should be followed, otherwise what is the point of having one?

[Gram]

Having had my afternoon 'constitutional' I now have a theory as to why the Eberspacher Airlectric will not accept reverse polarity mains.

 

It's control system needs to check that the sleeve around the heating element is earthed. This ensures that, in the event of the element breaking up, a path to earth is available to trip the protective device.

 

The control sytem checks that the sleeve is earthed by measuring the potential between the incoming mains Live and Earth wires. If the potential difference is insufficient (as would be the case if the earth was missing or the live input was at Neutral) then the control system isolates the Airlectric from the mains.

 

The system then thinks there is no mains connected and the heater fires up on diesel.

 

It's only a theory. I have no evidence at all to support it!

 

G

 

 

[lennyhb]

Am I missing something, Eberspacher are of German origin, the Germans wire their electrics with double pole switches & breakers, the Germans do not worry about reverse polarity. *-)

[spospe]

lennyhb - 2013-12-17 5:24 PM

 

Am I missing something, Eberspacher are of German origin, the Germans wire their electrics with double pole switches & breakers, the Germans do not worry about reverse polarity. *-)

 

The heaters are intended for universal use and thus comply with UK practice.

[Derek Uzzell]

If an Eberspacher Airtronic + Airlectric combination were deliberately designed to operate automatically on 230V power only if the mains power-supply conformed to the UK norm, this would assume that the Airlectric unit was to be marketed solely in the UK. This might be true, except there are Continental-European on-line 'sales' references to Airlectric that suggest otherwise.

 

There are quite a few other 230V heating systems intended for installation in motorhomes, caravans and boats and, to the best of my knowledge, all of these are polarity insensitive. My Truma C-6002EH heater has a couple of 230V heating elements inside it and 'reverse-polarity' does not affect its on-mains operation. If I run a fan-heater in my motorhome, that heater doesn't care about polarity. My fridge's heating-element happily operates on a reversed-polarity 230V supply.

 

Logically, then, one would expect the Eberspacher system not to be polarity sensitive, but Gram's and spospe's systems clearly are. I note that, in both instances, the motorhomes are Auto-Sleepers but I don't know if that's significant. It may well be that Auto-Sleepers is the only UK converter that installed Airlectric and I'm not aware that any non-UK converter did. So trying to establish whether an Airtronoc + Airlectric system works differently in another make of motorhome is probably not worth attempting.

 

I notice that Gram posted an Airlectric-related query to the A-S Owners Forum earlier this year, so he may wish to add a follow-up asking about the reverse-polarity issue. I suspect that every Airtronic + Airlectric system fitted to an Auto-Sleepers motorhome will react similarly to reverse-polarity, but it might be worth trying to confirm this via the ASOF and, in any case, if all A-S motorhomes with the system are polarity-fussy, it would be worth their owners being aware of this.

 

Earlier today I e-mailed Eberspacher asking if they could send me Airlectric technical documentation and whether they can advise on the reverse-polarity matter. I've just had an acknowledgement saying they will look into it and get back to me.

 

 

[lennyhb]

spospe - 2013-12-17 6:04 PM

 

lennyhb - 2013-12-17 5:24 PM

 

Am I missing something, Eberspacher are of German origin, the Germans wire their electrics with double pole switches & breakers, the Germans do not worry about reverse polarity. *-)

 

The heaters are intended for universal use and thus comply with UK practice.

 

So are you saying a German designed & manufactured heater is designed not to work in a German van.

I am not aware of any statements in the 17th edition of the regs that sate "if reverse polarity is detected by a device the unit must shut down"

[Brambles]

This is interesting because the electric heating unit uses ceramic ptc heaters. The unit is insulated and safe for reverse polaity and no metal sheath which can cause earthing issues. In effect double insulated. The input to the control units appears to be a 12 volt input to detect mains presence so is presumably getting a signal from the on board power supply/charger. But this is where the confusion lies in what happens if the onboard charger does not provide this signal.

Hopefully Derek will get an answer soon from Eberspacher. Information available online is very sparce, and not surpising as these are marketed as being fitted by authorised distributors for safety of the installation.

My guess is it is the on board charger which is detecting reverse polarity and not providing the required signal. As to working on uk or european mains, all they need to do is detect a voltage between the 'live' conductor and earth of greater than say 50 volts and if reversed then operation as described will work in both Uk and Europe, reverse polarity in europe not mattering. This is only a guess and my thoughts to day.

I know the OP is not interested in why or reason, but I am sure many will agree this is rather interesting from a technical point of view.

 

Looking forward to when Derek receives further information.

[spospe]

lennyhb - 2013-12-18 9:45 AM

 

So are you saying a German designed & manufactured heater is designed not to work in a German van.

I am not aware of any statements in the 17th edition of the regs that sate "if reverse polarity is detected by a device the unit must shut down"

 

No I am not. I wrote in haste and intended to say that probably equipment intended for UK use would comply with UK practice. After all, German designed and manufactured cars intended for UK use come with the steering wheel on the right, so why should not German designed and manufactured heating equipment be made to comply with UK practice when sold here?

[Brian Kirby]

But, the interesting thing is that, so far as I can see, there should be no risk whatever from the heater merely because the supply polarity is reversed. So, if one assumes correct polarity would apply in UK, and that units would only be used in UK, there would be no need for special accommodation within the heater for RP. Units supplied to continental manufacturers would not need to be any different, because the unit itself is (presumably) polarity blind, so would work equally well whatever the polarity.

 

That a UK installed unit doesn't work when polarity is reversed, suggests to me that presence of mains power is merely being detected by connecting the + feed signal to earth. Maybe, as suggested, by using the polarity indicator.

 

It will be interesting to see what reply Derek gets, as I assume there must be a relay/contactor switching the mains power to the heater element. It sounds a bit as though merely re-wiring the switching feed to the contactor across + and -, instead of + and earth, should allow it to function safely whatever the polarity. I agree Jon, it is intriguing.

[lennyhb]

spospe - 2013-12-18 10:25 AM

 

lennyhb - 2013-12-18 9:45 AM

 

So are you saying a German designed & manufactured heater is designed not to work in a German van.

I am not aware of any statements in the 17th edition of the regs that sate "if reverse polarity is detected by a device the unit must shut down"

 

No I am not. I wrote in haste and intended to say that probably equipment intended for UK use would comply with UK practice. After all, German designed and manufactured cars intended for UK use come with the steering wheel on the right, so why should not German designed and manufactured heating equipment be made to comply with UK practice when sold here?

 

But Motorhomes have wheels and can be driven anywhere in Europe (and further afield), So if you have an Eberspacher Airtronic fitted do you need a sign " Heating not to be used outside of the UK" - even if it is minus 20. :D :D :D :D

[Brambles]

The thing is Lenny m it would be quite simple to detect presence of power in both Europew and Uk by jus checking for a voltage between 'live'and earth of sy greater than say 50volts. As long as teh european floating earh was not closer to one of teh comductoirs by 50 volts than it would detect mains. Down side is in UK with tied neutral then reverse polarity means it cannot detect earth. However I am not sure this is what Eperspacher are actually doing.

It is also not beyond the realms autosleeper have wired up wrong or in a strange configuration.

[lennyhb]

I would back your last statement Jon, wouldn't surprise me if it's all down to Autosleeper but it all seams a bit weird.

[pepe63xnotuse]

Brambles - 2013-12-18 11:50 AM

It is also not beyond the realms autosleeper have wired up wrong or in a strange configuration.

 

To vote..press your buttons....NOW! ;-)

[Derek Uzzell]

Eberspacher have now sent me .pdf versions of the Airlectric Installation and Operating instructions. (If anyone wants copies, if you PM me with an e-mail address I'll send them to you.)

 

Eberspacher have also told me that "...it is correct that the Airlectric needs to know the live and neutral connection to ensure correct polarity."

 

So (as spospe and Gram have discovered) an Airtronic + Airlectric system IS polarity-sensitive and, if a reverse-polarity EHU is encountered, the Airlectric unit won't function until the 230V supply's polarity has been 'corrected' to the UK-norm.

 

(And, Yes, it still seems odd to me and, No, I don't understand why Airlectric NEEDS to be polarity-sensitive, and, No, I'm not going to ask Eberspacher why!)

[Brian Kirby]

Derek Uzzell - 2013-12-18 2:08 PM

 

Eberspacher have now sent me .pdf versions of the Airlectric Installation and Operating instructions. (If anyone wants copies, if you PM me with an e-mail address I'll send them to you.)

 

Eberspacher have also told me that "...it is correct that the Airlectric needs to know the live and neutral connection to ensure correct polarity."

 

So (as spospe and Gram have discovered) an Airtronic + Airlectric system IS polarity-sensitive and, if a reverse-polarity EHU is encountered, the Airlectric unit won't function until the 230V supply's polarity has been 'corrected' to the UK-norm.

 

(And, Yes, it still seems odd to me and, No, I don't understand why Airlectric NEEDS to be polarity-sensitive, and, No, I'm not going to ask Eberspacher why!)

Oh bugger! What a shame. Mark as unsolved.