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Discussion Starter #1
Hi All,

I want to put an anderson plug at the back of the patrol near the towbar, for ease of use for the compressor.

So I have a couple of questions:

do I need to run a negative cable from the battery or can I just earth it to the vehicle?

what gauge cable do I use?

do I need to have a fuse on the positive cable and if so what size?

Thanks!
 

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G'Day mate;
Yes you will need to run a neg. cable back to the battery.
6mil and no smaller for your wiring.
Your compressor should be fused now and you will need to fuse the line as close to the battery as practicle with a fuse no smaller than the one on your compressor, 15 amp should be ok.
regards Ian.
 

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Discussion Starter #3
Thanks for your help Ian.
 

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nissan
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Why does he need to earth back to the battery? Path of least resistance should be the body work and if its not you have earthing problems.

The fuse in the cable is to protect the cable from melting should the insulation cut through and generate a short - thus you should have a fuse sized to suit the size of the cable. My compressor wouldnt even start with a 15amp fuse. I'd need at least a 30 amp if not larger.
 

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nissan
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I've got an Anderson plug at the back for my campervan batteries, as well as being able to use a compressor, and I didn't run the negative back to the battery. There's no need to do so, just make sure that you pick a point on the chassis that gets good contact.

Cheers

Ray
 

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Wouldn't hurt to check a few body earths while under the vehicle, maybe even add on between the body and chassis as well(decent size too!)
 

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^exactly!
This would be the best option all around for your whole electrical system.
 

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Discussion Starter #8
Thanks guys much appreciated, will try earthing to the chasis first and if that doesn't work I will add some more earth points.
 

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I have just done the same as you to run my compressor. I have a 150Lpm compressor so I put my clamp meter on it and it draws 40A so I needed to use a 50A fuse. I also worked out the volt drop for 40A I need to use at least 10mm2 cable to keep it under .6 of a volt.

pl/a then use ohms law to work out the volts.

You should run a earth back to the battery because the GU's are known to have earthing problems.
 

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Running earth back to the battery is a bandaid solution to bad earth. A better option is to actually upgrade your vehicles earthing points. Battery to block, battery to chassis battery to body & body to chassis
 

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I ran a 10mm2 earth from the battery to the back of the car and mounted it to the body then got earth for the Anderson plug from that.
 

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Hi Fellas. Being an ex maniac I subscribe to the earth cable club. You can never have too good an earth. Accept that standard vehicle earths are not all up to scratch and deal with it. A poor earth will also encourage corrosion around the fault. A poor earth over a long run will cause voltage drop. Any fuse should be as close to the battery as possible. When running your positive cable to the rear, don't be mean with the cable size! Fat wire is good! Cheers, Derb.
 

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Hi Fellas. Being an ex maniac I subscribe to the earth cable club. You can never have too good an earth. Accept that standard vehicle earths are not all up to scratch and deal with it. A poor earth will also encourage corrosion around the fault. A poor earth over a long run will cause voltage drop. Any fuse should be as close to the battery as possible. When running your positive cable to the rear, don't be mean with the cable size! Fat wire is good! Cheers, Derb.
I'm with Derb it's not that hard to pull in a neutral when you do the active. But it would be a pain to have to do it twice. I am a sparky so I just went to my suppliers and got some orange mains cable. Also volt drop is a big issue with 12v because a 5% loss is only 0.6v so the resistance of your cables can only be 0.015 at 40A
 

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As the vehicle came from the factory, How many wires are connected to the negative terminal of the battery??

What does that tell you ??

:) ;)
 

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Make sure neg. wire of plug goes to good earth i.e make sure you remove paint/dirt and use appropriate cables and connectors.(at 40amps..big!) must be one helluva compressor but. Anyone done endless air on a G.U?
 

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Hi GUNewbie, as a number of members have posted, don’t use the chassis as the earth return, it’s simple playing Russian Roulette you negative supply.

While “most” chassis earth returns will work, there is no way to test in advance of an installation if the chassis is a suitable HIGH CURRENT circuit and just posting that vehicles come from the factory that way doesn’t cut it.

Vehicle manufacturers know exactly where they can get an earth return and even then it’s only for very low current devices like light globes.

There are very, very few vehicles that come from the factory that have high current requirements anywhere other than in the engine bay.

Furthermore, the newer the vehicle the greater the chances are for a bad earth return through the chassis.

As to the cable, if you want to provide both the current and voltage at a decent working level for you compressor, you need to run much thicker cable than the 6mm.

6mm auto cable, which is actually 4.5mm2, will cause at least 1.5v voltage drop while trying to run a 25 - 40 amp compressor.

You need to run at least 10mm2 twin or better still 6B&S twin ( 13.5mm2 x 2 ) and you can then use it in a dual battery system if you ever go down that road.

Also, you don’t need to protect the compressor as it should already be fitted with it’s own suitably sized fuse, so if you go with thicker cable, best protection would be a 40 amp auto resetting circuit breaker on 10mm2 cable and a 50 amp CB on 6B&S cable.
 

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What Drivesafe said, and...

IMHO run 6B&S, might cost a bit more now but nothing like "future" proofing for dual batteries, Camper/Caravan use or whatever

Rule of thumb to keep in mind for circuit protection. The Fuse (or C/B) size on the supply end is to protect the cable not the equipment so use a 40 or 50 Amp jobbie as suggested by others.

Equipment should be fused seperately either internally or at the connection end and not rely on the supply C/B.
 

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I wouldn't pay too much attention to what manufacturers do, there main concerns when designing a vehicle are to keep cost down and for ease of fitting on the assembly line.

In my opinion drivesafe post is on the money.

I don't know about you but I do not like the idea of scratching the paint from my chassis, the bloody things are hard enough as it is to stop rusting.
 
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