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Kate84

12 volt wiring need earth?

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Hi there! I’m new here. I have acquired a 1980s sprite which has been completely ripped out. I’m trying to sort the 12 volt wiring before I board the ceiling and walls.  I have bought twin flexible 1mm for lights and 4mm for usb/cig sockets. Do I need a separate cable for earth or does 12v not need an earth?  It’s going into a 2s4v distribution unit (1987) 

 

thanks in advance! 

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12v wiring is just positive and negative .

 

 

Dave

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Great thanks

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There are three types of 12 volt wiring.

SELV = Must not have an earth. (Separated)

PELV = Must have an earth. (Protective)

FELV = Can be either. (Functional)

ELV = Extra Low Voltage, i. e. 0 to 50 volt AC or 0 - 75 volt DC.

The class is really down to the battery charger, if the battery charger uses an isolation type of transformer then no need for an earth, and in the main battery chargers used in caravans do isolate from mains so in the main no need for an earth, and even if there was a need to earth one would earth the negative wire so still only 2 core cable required.

 

One thing to remember wiring a caravan you use flex, even for 230 volt wiring, do not use twin and earth.

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On 27/10/2018 at 20:49, Kate84 said:

Hi there! I’m new here. I have acquired a 1980s sprite which has been completely ripped out. I’m trying to sort the 12 volt wiring before I board the ceiling and walls.  I have bought twin flexible 1mm for lights and 4mm for usb/cig sockets. Do I need a separate cable for earth or does 12v not need an earth?  It’s going into a 2s4v distribution unit (1987) 

 

thanks in advance! 

First off I am no bright spark :D.

 

But a couple of thoughts\questions.

 

Is the 4mm for usb\cig sockets 4mm diameter per core ? Seems way too much.

 

As for twin and earth, would not 2. 5mm twin and earth be required for say a microwave or sockets that would accept 240v appliances e. g. a fan heater, electric fan, slow cooker etc. ?

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10 minutes ago, Sea&Sand said:

 

As for twin and earth, would not 2. 5mm twin and earth be required for say a microwave or sockets that would accept 240v appliances e. g. a fan heater, electric fan, slow cooker etc. ?

 

I think what ericmark is trying to say is that flex should be used throughout.

Solid core "twin and earth" is not flexible enough for caravan service as the conductors may crack over time.

 

So twin and earth flex, OK. Twin and earth cable, not OK.

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As said twin and earth cable will break as it does not flex  . 3 core flex is needed in tourer caravans for 240 v .

 

 

Dave

Edited by CommanderDave

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4mm is the cross section area of the copper, not the diameter. T&E is too rigid and can harden with movement causing cracking it must always be flex.

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I'm just installing an electric conversion kit for the marine bog on the boat, the current draw is 25A.   The run (combine length of + and -) is about 5m, I am using 6 sq. mm area tinned single core which is good for 50A.   The main thing to appreciate with 12V wiring is that there is a significant % voltage drop with lengths of 12V cabling, so always go for larger than the amperage rating of the appliance.  

It is not unknown for marine electronics not to function because of the voltage drop along a long run of cable (usually fail at <10V).

 

Edited by Guzzilazz

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27 minutes ago, Guzzilazz said:

I'm just installing an electric conversion kit for the marine bog on the boat, the current draw is 25A.   The run (combine length of + and -) is about 5m, I am using 6 sq. mm area tinned single core which is good for 50A.   The main thing to appreciate with 12V wiring is that there is a significant % voltage drop with lengths of 12V cabling, so always go for larger than the amperage rating of the appliance.  

It is not unknown for marine electronics not to function because of the voltage drop along a long run of cable (usually fail at <10V).

 

 

Boats, particularly narrow boats, need to have voltage drop taken into account in wiring sizes, just as caravan fridge wiring does - it's all because of the distance.

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For mains wiring fused or MCB at 16A ideally 2. 5mm three-core flex should be used but 16A is within the rating of 1. 5A flex if you have any supply difficulty. It does NOT need to be arctic cable (as what most EHU cable alludes to be) but it is an alternative source if you cannot find anything else. Note that mains power to fridges, microwaves, electric heating and cookers (if they have an electric hotplate) are usually connected by a 13A plug and socket in an adjacent cupboard for easy disconnection and removal in the event of a fault.

 

For 12V,  1. 5mm flex two-core should be enough for anything - it is difficult to draw more than 5A (the usual fuse rating for the 12V power socket and one assumes LED lighting will be used.) You do NOT (indeed should not) earth either side of the 12V supply.

 

For the hitch connection use the proper cable but from the internal connection point to the fridge 2. 5mm or 4mm two-core flex should be used it will pull in excess of 10A depending on type and size. The cables from the caravan battery to the fusebox should also be 4mm two-core flex with an in-line fuse close to the battery.

 

Note, in most applications the purpose of the fuse is to protect the cable, NOT the device or appliance it is feeding, hence why the battery fuse should be near the battery.

 

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