Polarity/Schmolarity

[kev54]

Ok, ok! So I dismissed all of the “never worried me in x00 years”-brigade on the basis that I have a modern motorhome with a sophisticated power management system.

I do now humbly apologise.

BUT in my defence, I plead that I was told the ‘van would blow up (or something like that) if I used an EHU with the red warning light on the Sargeant panel.

First, please note that if you have a dodgy, metal-handled hairdryer or somesuch - you will very probably electrocute yourself, reverse-polarity or not. Oh, and don’t use a metal knife to free a stuck piece of toast in a toaster… though actually … the rubber tyres that are between you and the ground might save you…

Frankly, I’ve not found a piece of kit I might have in my van that would be damaged by reversed polarity.

HOWEVAH, reverse-polarity seems to be a thing - particularly to the Sargeant E460 control panel in my 2013 Bessacarr.

Last week I was on a Spanish campsite and the red light lit up even when I used my clever reverse-polarity-reverser cable. (I’m very pleased with it, it has worked on quite a few French sites). I tried 4 other plug-in points - same red light, whichever way. Then I spoke with a nearby parked Brit who was running a TV on EHU. He said “all fine here for the last 24 hours, but I can lend you my polarity checker”. Woohoo! I tried the same outlets and each time had THREE lights lighting!

I went back to him as that option wasn’t covered by the fault diagrams on the back of the unit. He tried it in his caravan socket and also had three lights! He hadn’t actually used it to check before hooking up…

We decided to keep calm and carry on. We agreed that a) the supply was probably both reversed and lacking an earth, and b) it obviously doesn’t matter much.

So I thought I’d investigate.

Sargeant couldn’t be bothered to answer. The internet is all about house installation - but ignores the fact that France (to my certain knowledge) doesn’t care about polarity in household sockets because they have a different fuse system.

So - it seems it doesn’t matter very much - not in a motorhome anyway.

I’m SO very pleased that I bought those extra plugs and spent the time making the reverser cable. Sure what else would I be doing with my time away in a motorhome? Cheers all

 

[DBK]

It's all down to whether your RCDs are single or double pole. With a UK van it is possible they are single but hopefully, if it's a recent model, it won't be.

 

[kev54]

I’m over it. All of it

 

[kev54]

So it’s just an ‘abroad’ issue then Great! No problemo. Here’s a very delayed reply from Sargeant <<The reversed polarity light indicates that you do have reversed polarity at the mains input hook up lead. Usually this light will come on while you are abroad and it is directly linked to your mains charger as this is the only piece of equipment which is sensitive to it, however, as long as your charger and mains appliances are functional, you should be able to stay connected without any worries. For any further clarification, we recommend to seek advice from a domestic electrician.>>

 

[autorouter]

Here’s a very delayed reply from Sargeant <<The reversed polarity light indicates that you do have reversed polarity at the mains input hook up lead. Usually this light will come on while you are abroad and it is directly linked to your mains charger as this is the only piece of equipment which is sensitive to it, however, as long as your charger and mains appliances are functional, you should be able to stay connected without any worries. For any further clarification, we recommend to seek advice from a domestic electrician.>>

The reversed polarity light is a neon light that lights up if the voltage across it is greater than about 50V. It is connected between the neutral wire and the earth wire. If the polarity is correct, then the voltage between the neutral and earth will be zero, or a few volts at most. So the reverse polarity light stays off.

If the polarity has been reversed, and the neutral wire is now live, then there will be a voltage of about 230V between the neutral wire and the earth, so the reverse polarity light will light up.

It's likely that the site electrics were wired from a centre-tapped transformer, where the centre of the coil is earthed, and the 'live' and 'neutral' wires are equal and opposite. When one wire is +120V relative to earth, the other wire is -120V relative to earth. The voltage between them is 240V. This arrangement is used in the US, for higher powered appliances, and the smaller appliances just use one half of the transformer, ie 120V.

Because the voltage between both of the wires and earth is more than about 50V, the reverse polarity light will light up, whichever way round the wires are connected. This is also the reason your socket tester will show both lights on.

Reverse polarity was never a function issue, it's 'only' a safety issue. Properly specified modern motorhomes have a supply panel with a 2-pole RCD and 2-pole MCBs, and are much safer than older or DIY-converted ones that may have single-pole RCDs, RCBOs and MCBs. If the motorhome has UK 13A plugs then they have a fuse in the plug, which is a single-pole device, and could be a risk if the polarity is reversed. However a 2-pole RCD will largely eliminate that risk.

And you're right, a polarity reversing lead won't make any difference with a centre-tapped supply.

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[Raul]

I disagree, a split phase center tap, it has a true neutral. One end is positive one negative, and in the center is balanced/ neutral. A fourth wire will be earth, and 0v between neutral and earth.
In EU and UK you have two wires, a life wire and PEN. These two can be reveresed either way up to PEN separation into PE and N protective earth and neutral. Neutral here gets bonded to earth rod.
Not All EU have separation like in UK. Some do some don’t. When there is no separation, no rcd will work and no earth connected, but double pole everywhere. It’s very common this practice I have seen it many times.
In this case you will get reverse polarity( what we call that) either way, as there is no N.
Neutral is derived from PEN separation.

 

[Pausim]

Reverse polarity is a UK thing. Most of the rest of the world does not use a system that relies on single pole fuses and switches in plugs and spur outlets. Motorhomes travel to other countries and need to be designed to world standards not just UK ones. A polarity light suggests that the motorhome has been designed to UK standards where polarity matters not to the wider 2 pole (double isolated) standards.

 

[kev54]

Reverse polarity is a UK thing. Most of the rest of the world does not use a system that relies on single pole fuses and switches in plugs and spur outlets. Motorhomes travel to other countries and need to be designed to world standards not just UK ones. A polarity light suggests that the motorhome has been designed to UK standards where polarity matters not to the wider 2 pole (double isolated) standards.

Hmm. I think I understand what you’re saying, but Sargeant didn’t appear (to me) to say that. They mentioned it as a warning with no indication (to me) of danger - though it was a rather ‘Pontius Pilate’ answer. Do you really feel a 2013 vehicle is in (electrical) danger outside the UK?

 

[Pausim]

Hmm. I think I understand what you’re saying, but Sargeant didn’t appear (to me) to say that. They mentioned it as a warning with no indication (to me) of danger - though it was a rather ‘Pontius Pilate’ answer. Do you really feel a 2013 vehicle is in (electrical) danger outside the UK?

No as long as you do not rely on the single pole switches to isolate appliances. The way the continental manufacturers cope with our 13A plugs is to use sockets without switches, that way no one can be fooled into thinking that flicking off the switch makes things safe. Hopefully your distribution board RCDs and breakers are 2 pole.

 

[Orion]

I’m over it. All of it

Wise man. Take a chill pill - aka glass/bottle of your preferred, and enjoy life.

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[kev54]

No as long as you do not rely on the single pole switches to isolate appliances. The way the continental manufacturers cope with our 13A plugs is to use sockets without switches, that way no one can be fooled into thinking that flicking off the switch makes things safe. Hopefully your distribution board RCDs and breakers are 2 pole.

Finally, light dawns in my little brain! Thanks Pausim. I, too, hope they’re 2-pole. I’ll see if I can find out.

 

[autorouter]

I disagree, a split phase center tap, it has a true neutral. One end is positive one negative, and in the center is balanced/ neutral. A fourth wire will be earth, and 0v between neutral and earth.
In EU and UK you have two wires, a life wire and PEN. These two can be reveresed either way up to PEN separation into PE and N protective earth and neutral. Neutral here gets bonded to earth rod.
Not All EU have separation like in UK. Some do some don’t. When there is no separation, no rcd will work and no earth connected, but double pole everywhere. It’s very common this practice I have seen it many times.
In this case you will get reverse polarity( what we call that) either way, as there is no N.
Neutral is derived from PEN separation.

I came across a centre-tapped transformer supply on a site in Spain, maybe the same one as the OP but I don't remember where it was. I measured the voltage from the earth wire, and it was equal voltages to both the 'live' and 'neutral' wires. So such systems do occur in reality.

However I agree that the other system you describe, with the supply coming from an isolated transformer and neither wire connected to earth, will also show the same symptoms. The voltage of either wire relative to earth will be a random value, very likely enough to switch on the 'reverse polarity' warning light with a normal connection or through a polarity reversal adapter. And from what you say, much more likely than a centre-tapped system.