# Hook up cable at home



## spence (May 25, 2008)

Hello,

Just made a new cable at home as I have an old outside connection but i have reverse polarity showing on the electrical box.

Armour cable from the consumer unit (32amp Fuse) it used to run a hot tub but thats another story  to an outside switch. then a new 3 core cable to the motorhome with a standard hook up end.

I have reverse polarity even when i switch the live and neutral over!!

Is it really telling me it cant find an earth?

Spence


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## Evs54 (Mar 11, 2013)

spence said:


> Hello,
> 
> Just made a new cable at home as I have an old outside connection but i have reverse polarity showing on the electrical box.
> 
> ...


Worth you getting an electrician to do a Earth Loop Impedance test on your system .


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## Techno100 (May 8, 2010)

If it is feeding outside equipment it needs an RCD or RCBO. A fuse will not protect you from earth leakage and if there is no earth it will go through you to get there :lol:


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## spence (May 25, 2008)

My mate (Electrician) is popping in tomorrow to have a look. Better safe than sorry or worse!

Thanks

Spence


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## caz650s (Feb 15, 2009)

I had the same problem when plugged into our detatched garage .. I traced it to a broken earth wire in the junction box in the house where the cable to the garage is connected !! ... I guess the sockets in the garage have had no earth all the years i have lived here!! .. good idea for Autotrail to have a reverse polarity warning lamp on the consumer / charger unit.


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## listerdiesel (Aug 3, 2012)

You need to have your house wiring in a reasonable condition to comply with your house insurance, and a regular walk round checking the RCD's is time well spent.

Peter


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## steco1958 (Mar 5, 2009)

spence said:


> My mate (Electrician) is popping in tomorrow to have a look. Better safe than sorry or worse!
> 
> Thanks
> 
> Spence


Could not agree more, always get an expert in when it can hurt you, i.e electrics, gas, and brakes


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## rosalan (Aug 24, 2009)

I have just bought a polarity testing plug. Checked the van... reversed polarity!! Checked the garage .... fine. Stripped the bought cable and at one end the line and neutral were reversed.
I cannot now recall where I bought it but judging from the way it was connected, that is how it left the assembly line.
Well worth getting one of those little polarity testing plugs.

Alan


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## Techno100 (May 8, 2010)

There are those who care about polarity and those who don't :lol:


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## spence (May 25, 2008)

Techno, should I? The connection is for at home hook up only to keep batteries charged, fridge & freezer running.

Spence


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## pippin (Nov 15, 2007)

Yes of course you should have cables connected correctly.

The order of importance of the 3 cables is:

Nr 1] The earth connection

Nr2] The earth connection

Nr3] The earth connection

Why?

Because if the line or neutral are faulty then you know about it because appliances simply won't work.

If the earth is faulty then the only time you get to know about it is when you are dead due to another fault.

Oh, and "polarity" means nothing where AC is concerned, as I have patiently tried to explain on a number of other posts.

Even my suggested alternative of "polarisation" is not really correct either.

Perhaps "reverse connection" is better.

Polarity is important (usually) your 12V DC circuits.


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## Evs54 (Mar 11, 2013)

pippin said:


> Yes of course you should have cables connected correctly.
> 
> The order of importance of the 3 cables is:
> 
> ...


Polarity in a domestic AC installation is also very important as any Electrician would know .


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## listerdiesel (Aug 3, 2012)

It isn't 'polarity' per se as AC has no polarity at all. 

It is how the AC supply is referenced to Earth that is important.

In a domestic house:

Line is always the outer end of a 3-phase leg of a star-connected transformer, where the neutral point is earthed at the point of entry into the house. The 3-phase transformer is in your local sub-station, where it comes down from 11kV 3-wire three-phase Delta to 415V 3-phase Star.

So with reference to Earth you have 230V on the Line connection and 0V on the Neutral.

On any circuit connected to these two points, current flow is equal in both conductors when the circuit is turned on. An earth leakage would create an imbalance in the two conductors which is what is used to operate RCD breakers.

So with reference to Earth, the Line connection must ALWAYS be 230V and the Neutral must ALWAYS be 0V.

You cannot do the same thing with small generators.

Because your motorhome is in reality an 'Appliance' as far as the supply goes, it needs to follow the conventions as far as Line and Neutral and Earth connections.

As an aside, most machinery that uses three-phase does not use the Neutral connection at all, and it is classed as 3-wire 3-phase plus Earth, but when required, it can be provided from the inlet main fusebox in the premises.

Peter


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## H1-GBV (Feb 28, 2006)

People do some "funny" things with electrical wiring. 

I came home once to find a builder friend perpetually getting "little shocks" whenever he touched his electric cement mixer (whilst wearing thick rubber boots!).

He had "saved" money by using a 2 core extension lead, joining the earth terminal to neutral at both ends: "neutral is 0V and so is Earth, so there is no need for separate wires". 

Some time ago he'd had an "accident" and cut the wire in half. "Fortunately" he "remembered" some of his school science: "red goes to black and black goes to red", so that is how he joined them using a terminal block. [Why did he think the wires would change colour exactly at the place where he'd cut the wire?]

So now the neutral wire was joined to the Earth at the plug end, the live and neutral "swopped" at the joint and so the Earth was joined to the live wire at the socket. Plugging in his metal-framed cement mixer ensured that everything he touched was live!

IF you don't understand electricity, don't try to save money by "doing it yourself"! :wink:


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## rayc (Jun 3, 2008)

Evs54 said:


> pippin said:
> 
> 
> > Yes of course you should have cables connected correctly.
> ...


I shall ask my friendly electrician when I see him next.


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## pippin (Nov 15, 2007)

Listerdiesel - Peter has just given you the most succinct resumé of the situation - here in the UK.

What he didn't add (slap-on-the-wrist!) was that in many other countries the same situation does not always obtain.

_"So with reference to Earth, the Line connection must ALWAYS be 230V and the Neutral must ALWAYS be 0V."_

In other countries:

Neither line nor neutral may be tied to anything by the time it arrives at the user, be that a house or an EHU socket.

The blue wire might be line and the brown wire neutral w.r.t. to earth.

Or they may be floating anywhere between.

The only thing that is certain is that there is 230V AC between blue and brown.

That is why most modern €U electrical installations have dual pole RCDs/RCBOs and double pole light and socket switches.

That is why we (need to ?!) use (so-called but innaccurately named) polarity testers because by and large UK MHs have only single pole RCDs/RCBOs/Switches.

We need to ensure (for the safest situation IN CASE OF A FAULT) that the cable that is closest to earth potential is the one that goes to the neutral side of our MH consumer unit.

PS

This is so important that I usually remember to "polarity" test the EHU only when disconnecting as we leave a site!


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