what size wire

Submitted: Friday, Jun 23, 2006 at 12:46
ThreadID: 35213 Views:5292 Replies:11 FollowUps:27
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Wanna run a power wire down the back of the car from second battery for -
the fridge
2 ciggy lighter plugs (charging batteries etc)

The inverter (charging batteries etc) or should this have a seperate power wire?

what size wire SHOULD I run as a minimum?

Auto elects are something that really bleep in baffle me...

love u long time $2.00+gst.
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Reply By: Member - Sam (NSW) - Friday, Jun 23, 2006 at 12:51

Friday, Jun 23, 2006 at 12:51
Bruce,

I ran 8 gauge from the aux. batt, through the firewall, along the cable channel in the floor pan to a couple of fuse blocks at the rear, i can then hook the necessary accessories up to that (fridge, inverter, lights etc). i bought the 8 gauge from jaycar and the rest of the bits from supercrap, repco or one of the places like that.

The 8 gauge is rated to about 50amp i think from memory (could be wrong), so thats enough to handle anything i am likely to draw plus allow for any voltage drop along the run

cheers,
Sam.
AnswerID: 180057

Follow Up By: Flash - Friday, Jun 23, 2006 at 13:03

Friday, Jun 23, 2006 at 13:03
The amp rating sadly means diddly squat. It has only to do with heating of the wire, and you could for example run higher amps depending on cooling the wire.
What you have to consider is voltage drop!
Bruce, I would consider running two separate wires, 6ml minimum, one for the fridge and the other for your other outlets.
Also be carefull- some wires rate on overall size rather than copper conductor size. (plastic is cheaper than copper).
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FollowupID: 436253

Follow Up By: Member - Jeff M (WA) - Friday, Jun 23, 2006 at 13:14

Friday, Jun 23, 2006 at 13:14
8 Guage is a decent size wire, I'd probally be happy with that. Personally I have 4guage going to the rear storage box to the third battery, then 8 guage to the inverter (mounted to the storage box) and two lot's of 6mm to the rear section where the Fridge, Water pump and 3 ciggy lighter plugs are (it's not far, probally only a meter or so from the 3rd battery).

Basically don't worry about wire rating (as said by Flash) cos it's all bull bleep . Just get the biggest thickest mother wire you can afford and is practicle to run through the car and go that way.

I'm not sure what type of inverter you are running, but they can draw some absolutally KILLER amps. Mines a 450w PureSinewave and from my calculations in can draw at least 45amps continuously at full load, that is hell of a lot of amps. Make sure you're wire is up to it. Also, peak loads on inverters need to be considered too.

If I were you I'd go at least the 8g for the inverter (basically car stereo amp power cable) and a couple of 6mm's for the rest, or run some 4g all the way (expensive).

Obviously I'm a little over kill, but I have mucked around with a huge amount of battery setups and wire configurations in the surf to try and handle all my toys and found that major overkill is the best way to go. You get stuff all voltage drop (you're batteries last longer while setup for camp) and when you add the next gaget (which you always will) you don't have to run more wires to the back.
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Follow Up By: Leroy - Friday, Jun 23, 2006 at 13:14

Friday, Jun 23, 2006 at 13:14
I ran 8G also. Got it from DSE. Similar to the Jaycar cable that Sam used. I even run my compressor through it.

Leroy
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FollowupID: 436258

Follow Up By: Skinny- Friday, Jun 23, 2006 at 13:42

Friday, Jun 23, 2006 at 13:42
Interested how to connect 8 gauge to a ciggy lighter. Did you use a step down piece of wire or some clever connectors.
SKinny
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Follow Up By: Member - Jeff M (WA) - Friday, Jun 23, 2006 at 14:13

Friday, Jun 23, 2006 at 14:13
"Interested how to connect 8 gauge to a ciggy lighter. Did you use a step down piece of wire or some clever connectors. "

That's why I ran 6mm from storage box to the rear, just makes it simpler. The other way around it is to buy a 6 way fuse box (boat fuse box's are great). They have a bolt to attach a 4g or 8g crimp to, then have fused screw temrinals to run you're thinner wire to the different accessories.

That way you can have, ciggy lighter 1, 2, 3, and fridge plug, water pump etc etc or similar, all indivdually fused.

Maybe somthing like this, the 12 volt shop sells these:
<img src="http://members.westnet.com.au/themeads/pictures/host/fuse box.jpg"
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Follow Up By: Skinny- Friday, Jun 23, 2006 at 14:14

Friday, Jun 23, 2006 at 14:14
Mighty nice , will have to look for one as well. Thanks

Skinny
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Follow Up By: Leroy - Friday, Jun 23, 2006 at 15:01

Friday, Jun 23, 2006 at 15:01
there's terminal blocks from car stero places where you can connect your thick wire like 4g/8g and it has outlets for small wire.

Leroy
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FollowupID: 436281

Reply By: Alloy c/t - Friday, Jun 23, 2006 at 13:26

Friday, Jun 23, 2006 at 13:26
Truckster ,dont ef around with it ,do it properly the 1st time , 6 preferably 8 mm squared . thats the core ,not including insulation , run both pos and neg to battery ,your going to run the fridge so the last thing you want or need is wire that is too thin causing voltage drop... the right size wire wont exactly be cheap ,should be round $5/6 per metre from a 12v specialist store like the 12volt shop.
AnswerID: 180065

Follow Up By: gav99x - Friday, Jun 23, 2006 at 14:38

Friday, Jun 23, 2006 at 14:38
Okay, yesterday I went to my local Jaycar and picked up some quality looking wire (I thought!) to hook up my spotlights, it's Jaycar brand, rated at 25A and is 8 guage...cost $0.70 per metre. What would be the difference between this stuff and the $5-$6 gear you mentioned Alloy c/t? Appears to be a good quality multi-strand wire (quite flexible).

Gav
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Follow Up By: Alloy c/t - Friday, Jun 23, 2006 at 15:41

Friday, Jun 23, 2006 at 15:41
gav99x 70c per metre rated at 25amp and is 8 guage ,,,might be rated at 25amp max and they call it 8 guage but Iwill bet you that it is not 8mm squared in the actual wire ,, the $5/6 from 12volt shop is twin core tinned and 8mm sqared at the core ,not overall dia , whole point of the excersize in transfering power from under the bonnet to the rear is to NOT have any voltage drop ... how big a spotlights you planing on running with your" 25amp" wire ,,
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Follow Up By: gav99x - Friday, Jun 23, 2006 at 15:52

Friday, Jun 23, 2006 at 15:52
Thanks alloy c/t. Sorry should have mentioned the cable is single core only, and not tinned. I've hooked up Narva blue Ultima 175's with it so far which are 100w globes and is seems to operate quite well. Am now hooking up 100w fog lights for those foggy country roads hence the extra wire purchase yesterday.

Excuse the ignorance with regards to the 8mm2 measurement, but is this a physical measurement i.e. 2.8mm x 2.8mm = 8mm2? If so this wire from Jaycar would be pretty close to that, about the same I'd say.

I've always bought tinned wire when installing 12V on my boat due to water/salt etc., is there a strong case for using it in vehicles also?

Thanks again
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FollowupID: 436297

Follow Up By: Alloy c/t - Friday, Jun 23, 2006 at 16:04

Friday, Jun 23, 2006 at 16:04
gav99x ,tinned = no chance of of copper verdigris so better long term conductivity ,applies = to boats and 4x4 .. 8 mm sq is the wire size with all insulation removed ,IE bare wire.,is also the perfect size fit for standard 50amp anderson plugs.
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Follow Up By: Truckster (Vic) - Friday, Jun 23, 2006 at 16:47

Friday, Jun 23, 2006 at 16:47
I got a techno chubby reading that.
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Follow Up By: Alloy c/t - Friday, Jun 23, 2006 at 18:06

Friday, Jun 23, 2006 at 18:06
Truckster , only trying to show that "wire aint wire " with apologies to Hoges "thats not 8mm wire ,now this is called 8mm wire" ..as I said earlier , do it right the first time so you wont be efed around later with " my fridge dont work right" and your young fellas "beer" [softdrink] is not to temp.
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FollowupID: 436320

Follow Up By: conman - Friday, Jun 23, 2006 at 18:19

Friday, Jun 23, 2006 at 18:19
never thought to run the ground back to the battery. is this theory or does it make a difference to the voltage drop?
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FollowupID: 436321

Follow Up By: Alloy c/t - Friday, Jun 23, 2006 at 18:40

Friday, Jun 23, 2006 at 18:40
Conman ,no its not just a theory , vehicle makers try to save 1c here and 2c there and for costings sake use the vehicle body as the ground return on all non critical electrics , as an example just look at your headlights ,just upgrading the wiring from the factory fitted minimum will negate the need for spotties , try it youself ,run an extra neg wire straight from your h/light to the batt neg terminal ,you will see the light.
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FollowupID: 436325

Follow Up By: Member - Glenn D (NSW) - Saturday, Jun 24, 2006 at 23:04

Saturday, Jun 24, 2006 at 23:04
Dont really want to run it 'straight' to the battery , must have fuse on the posative.

From my second battery I have a terminal strip on the fire wall with allowance for 10 outputs , I use 5 , 1 of which is twin core wire that runs in flex conduit down the chassis rail to near the tow bar , it ends in a plug , I have made a fly lead with a cigarrette lighter socket which let me use a flouro light or frige outside ( a 12v tv , but dont tell anyone ) with the car locked up , good for when you leave camp with the fridge in the tent .

Glenn.
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FollowupID: 436471

Follow Up By: Member - Glenn D (NSW) - Saturday, Jun 24, 2006 at 23:08

Saturday, Jun 24, 2006 at 23:08
forgot to say am only running 6mm square , but not running much off it at once !
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FollowupID: 436472

Follow Up By: Truckster (Vic) - Sunday, Jun 25, 2006 at 23:47

Sunday, Jun 25, 2006 at 23:47
What if I ran seperate 6mm wires.

1 for each fridge plug, and 1 for the ciggy lighter plug and 1 for the inverter?

would that be sufficent? That way I have seperate circuits for each one if things go poo... ?

Thanks
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FollowupID: 436589

Follow Up By: Alloy c/t - Monday, Jun 26, 2006 at 14:46

Monday, Jun 26, 2006 at 14:46
Truckster ,why run 3 x 6mm ? , 1 x 8mm dual core is easier ,will do the job and the at the end you just run it into the fuse box that you "will use" for all the plugs down the rear end ,, ,,, I see that further down Crazie has got some stuff for you , 12v is not rocket science ,just a bit different to AC.
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FollowupID: 436659

Follow Up By: Truckster (Vic) - Monday, Jun 26, 2006 at 16:30

Monday, Jun 26, 2006 at 16:30
thought of the 3 seperate wires for seperate circuits...
so if anything goes pearshaped, I would still have power..

already talked to ads about it today.
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FollowupID: 436667

Reply By: Member - John L G - Friday, Jun 23, 2006 at 13:32

Friday, Jun 23, 2006 at 13:32
I understand from the auto electricians that 8BSS is the requirement for your job and often only available from sparky outlets-not hardware or accessory outlets.

Wire brought at some outlets may give gauge in mm's but may refer to overall diameter including plastic casing and amps quoted on packaging is not for continuos current. As the gang above state, the voltage drop can be substantial over a distance and beefier wire is the answer.

Golden rule "If in doubt - go up a size" and don't scrimp on $'s
AnswerID: 180069

Reply By: GaryInOz (Vic) - Friday, Jun 23, 2006 at 14:28

Friday, Jun 23, 2006 at 14:28
Get one of those 4 Ga or 8 Ga sets the car audio guys use from JB hifi. About $50-70 (90% of the bits, with half the work done for you). Only need to buy an additional earth wire back to the battery (Bursons). You can use the trigger wire that comes with the audio set to trigger a solenoid isolator if you dont have a proper dual battery charger (Pirhana, etc).

Be aware:
150 watt inverter will draw ~14 Amp
300 watt inverter will draw ~25 Amp
600 watt inverter will draw ~49 Amp

all at full power output. Count up the number of watts at 240 Volts your appliances need, add 50%, and go for the next inverter power output size up from that.
AnswerID: 180082

Reply By: Member - Athol (NSW, 2527) - Friday, Jun 23, 2006 at 14:30

Friday, Jun 23, 2006 at 14:30
Trucky as has been said dont FF around!!

I have run 16mm welding cable from the main battery tru a solenoid down through the chassis rail and out the back to an anderson plug. No voltage drop there.
The welding cable is double coat with insulation so it wont wear thru and the cable just fits into the anderson plug lugs.

Oh and I aquired the welding cable in blue and black for easy identification of pos. and neg.

Hope this helps
Athol
AnswerID: 180083

Follow Up By: steve+h - Friday, Jun 23, 2006 at 19:40

Friday, Jun 23, 2006 at 19:40
Athol
what part of 2527 are you from. I just moved to the rainy gold coast after 8 yrs there

Steve
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FollowupID: 436346

Reply By: RedGibber - Friday, Jun 23, 2006 at 19:50

Friday, Jun 23, 2006 at 19:50
Hey Bruce,

I run figure-8 red/blue at 10mm2 from Triangle Cables. This stuff is used by various major telcos for powering eqpt, and you may be pleasantly surprised at the price!! My company purchases lots of this sort of cable as we do installs for the telcos here in WA, as do others across all of Oz. This mob's also in Melb. so give 'em a call on 9676 6066.

I'll get a piccy and email it to you if you like. Terminal connectors (lugs, bootlace etc.) are readily available at Lawrence & Hansons and other joints, as are the whole range of Anderson connectors.

Cheers
RedGibber
AnswerID: 180128

Reply By: disco1942 - Friday, Jun 23, 2006 at 22:10

Friday, Jun 23, 2006 at 22:10
As Alloy c/t said "wire aint wire." for further reading on this subject try tinyurl.com/rjumf .
This was written by a bloke who has extensive experience in the automotive industry.

With regards to the rule “don't use the body as an earth return” - this only applied to the older vehicles where the bodies were bolted together. Unfortunately although bodies have been spot welded together for over fourty years this rule still raises its ugly head. The body return is anexcellent way to go if you can establish good earth points in close proximity to your load. If you do not use a body return you have to double the size of the wire used.

PeterD
PeterD
Retired radio and electronics technician

Lifetime Member
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AnswerID: 180148

Follow Up By: Member - Mike DID - Sunday, Jun 25, 2006 at 16:23

Sunday, Jun 25, 2006 at 16:23
I measured the resistance in the body from the right rear to the battery in an NP Pajero - it was equivalent to 4Gauge wire ! So if you used 8Ga or 6Ga you would have MORE voltage drop than using the body.

In any modern car EVERY electrical device (except the Starter Motor) is earthed via the body - it WORKS.

If you really need to run an earth wire back to the Battery, at least earth it at the rear also to minimise voltage drop.

Mike
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FollowupID: 436523

Follow Up By: Alloy c/t - Sunday, Jun 25, 2006 at 18:12

Sunday, Jun 25, 2006 at 18:12
And so MikeDiD by you reconning just running a + wire from the batt and using the body as the earth is good enough ,,funny how copper is a better conductor tha steel ,ally ect ect , and EVERY 12v fridge manufacturer recommends a Direct connection to the battery ,, there is no way that a vehicle body with earth take offs all over the place is as effective as a straight to battery connection ,
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FollowupID: 436535

Follow Up By: Member - Mike DID - Sunday, Jun 25, 2006 at 18:21

Sunday, Jun 25, 2006 at 18:21
Anyone who thinks my measurements are wrong can try it for themselves.

Mike
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FollowupID: 436537

Follow Up By: Alloy c/t - Sunday, Jun 25, 2006 at 18:38

Sunday, Jun 25, 2006 at 18:38
Well bring your paj around and we can try it with my multimeter ,OH I forgot ,Its a pajero thats made of this magic metal that conducts electricity better than any other vehicle ever built , better make sure you never drive in a thunder/lightning storm.
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FollowupID: 436542

Reply By: Muzzgit (WA) - Saturday, Jun 24, 2006 at 00:51

Saturday, Jun 24, 2006 at 00:51
Truckster, my two bobs worth.

Using 6mm cable, as found in auto part places, it would be best to double to the rear of the car + and - both through seperate fuses or circuit breakers.

One for fridge, one for others.

Or one big bugger to a fuse box, which would be easier to add onto later. You may even need to go under the car, not through it!

I have one 6mm run to two plugs at the back of my GU, and sometimes at night when using the fluro plugged in next to the fridge, the light would go out for a short period. It took me a while to realise that it wasn't a dodgy fluro, but the circuit was tripping when the fridge cut in.

Now I have a seperate run just for the fridge which comes out at the rear of the centre console [I wanted it as close to the battery as practicle] and the rear plugs are now just for the fluro and charging re-chargable fluro.
AnswerID: 180157

Follow Up By: Member - Glenn D (NSW) - Saturday, Jun 24, 2006 at 23:17

Saturday, Jun 24, 2006 at 23:17
Posted my other answer before reading yours , this is my setup also.

V good cutout at rear of centre console !!

Although you dont need fuses on the return or neg wire !

Glenn.
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FollowupID: 436473

Reply By: Flash - Saturday, Jun 24, 2006 at 21:56

Saturday, Jun 24, 2006 at 21:56
Look at this Bruce.... very handy....
Site Link
AnswerID: 180229

Reply By: arewelost - Sunday, Jun 25, 2006 at 23:22

Sunday, Jun 25, 2006 at 23:22
hi
its alright running from a ciggy lighter but you have a major problem the std wiring for a ciggy lighter is 1.5 mm square you will either blow the fuses or melt the cable take the supply direct from the battery and i agree biggest is better
AnswerID: 180333

Reply By: Member - Crazie (VIC) - Monday, Jun 26, 2006 at 12:29

Monday, Jun 26, 2006 at 12:29
i got what you need big bou, ring me
AnswerID: 180393

Follow Up By: Truckster (Vic) - Monday, Jun 26, 2006 at 12:37

Monday, Jun 26, 2006 at 12:37
call me back tart..
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