Hi,

I am designing a wiring harness lto fit a V6 as a unversity project. I am not changing the ECU harness but completely starting from scratch for the rest of the car. Does anyone know of a website or have any other literature that would list the current draw from each electrical component on the car so I can work out cable thickness and fuse ratings.

Thanks

Dan.

these things will all vary depending on car type.

Why dont you get hold of a Haynes manual? You can get all the fuse values there!

Your wiring should always have a greater current rating than the fuse - as a guide.


atb


steve


PS - if you are cheap, why not take a look in a scrap yard - but it might be hard to verify which fuse does what. some cars are dumped with original owners guides in em.

It's not too complicated - most cable suppliers divide their range into size and usage: For example, look at:

vwp-cables

It tends to spilt into

Thin stuff - indicators, warning lights, brake lights, etc.
Thick stuff - horns, headlights, etc.
Very thick stuff - battery to alternator links.

An over-simplification maybe, but not far off!

Also look at

premier-wiring

They sell the most modern thin-wall cable that will carry more current for a smaller size - makes the loom smaller! Their site is a bit vague, but it is really worth getting their catalogue, as it has recommended sizes, colours, etc. plus lots of switches, connectors, etc.

Have fun!

David
(who's busy making his own wiring at the moment)

Thanks for your help. I'll give them a go.

Dan.

it gets a lot more complicated, David.

Thick stuff isnt always as good as thinner stuff.

I have used something called tri-rated cable on my car. it carries - guess - 3 times more than a std type.

You cant really guage capability on size that well.

1mm cable could do say 3a or 11a depending on type.

take a look on

http://rswww.com

or

www.farnell.co.uk

or get vehicle witing product's brochure.


modern cars have really really thin wire. If you use that as a model without the high rated cable, you might have a barbeque rather than a car!

I think from memory most of my wire is tri rated, carrying either 11a or 20a.

atb


steve

OK Steve, I know I over-simplified!

I hadn't chosen the cable purely on size - I looked at the rating and matched them to the task. What I was trying to say was that places like Lightning Looms sell the "traditional" cable which is quite thick. Does the job, but takes up space.

Other places like Premier Wiring are now selling the "thin" cable, which has thinner and better PVC sheathing. The wire inside can be thinner because it can lose heat faster than in the traditional stuff. The new sheathing is also tougher, more resistant to abrasion and tolerates a higher temperature (105C, I believe).

As most establishments sell their cable at roughly the same price, I thought that I'd go for the higher-spec stuff! It is remarkably small for its rating.

rgds,

David

agreed David

it must be ok, but that really thin stuff on cars nowadays makes me worried its gonna chafe and short out.

Funny thing about tri rated cable is its actually thicker walled than the standard stuff!

atb


Steve

I could be missing something here, but I though tri-rated meant it complied with Euro, US, and Canadian standards...ie: 3 ratings in one cable.

quote:

---

Originally posted by Alan B
I could be missing something here, but I though tri-rated meant it complied with Euro, US, and Canadian standards...ie: 3 ratings in one cable.

---

Not that it matters, but I did some research after my post just to see if I was dreaming.

http://www.concordia.ltd.uk/tri_rated/

Seems to concur with me, although I'd agree your names for it would make more sense.

I think many companies use it so they can sell machines almost anywhere in the world because having the multiple approvals.

Its quite often that UL approval on its own is good enougth, as is the Canadian CSA standard.

But you are right - using cable with as many approvals as possible is a good thing.

atb


steve

No i think the point alan was making was that your wrong about tri rated not being three times greater at carrying current, i thought you were meant to be an electrician

red ter red.....black ter black......blue ter fxxxk

quote:

---

Originally posted by Highcost builder
No i think the point alan was making was that your wrong about tri rated not being three times greater at carrying current, i thought you were meant to be an electrician

---

cable is important to me........i weighed in so much copper in the late 80's.......that i paid off me mortgage...........but regardless of yer wirings capacity......theres nowt really on a locost....headlights.horn.on a relay....bit of thick wire off the batery.......bobs yer uncle...and fanny's yer uncles live in lover....sorted

Handbags at dawn!

well steve when i completed my electronics at uni i seem to recall being taught all about current carrying capacity after all without cables we would struggle to get power to the PCB's, unless im wrong again.


Trouble is there are to many smart arses and not quite enough knowledge to fill them all.

thats true, hicost.

But, when we design industrial machinery (and Im 43 and a bit past uni days when tri-rated probably wasnt around) we do it as a team. I and the other design engineers specialise in the microelectronics side. As Technical Director, I cant be involved in all aspects.

Someone else wires up the machines and does the control side. Usually the technicians on a project.

So as far as i'm concerned, if the wires carry the signals to my boards, are approved for the market we are selling in, and carry the current needed, thats all I PERSONALLY need to know! Other people are paid to know and take account of these areas.


Do you have an RS catalog? I found out something interesting today.


Look at the tri-rated cable sized at 1mm. Carries 17 amps.

Look at their normal equipment wire at 1mm size. 6 amps.

Thats just about 3 times the rating isnt it?

If you look in the same catalog, it tells you that the tri rated cable is approved to multiple standards. In fact, far more than three.

Confused?

I should have been.



atb


steve

Getting back to the topic (rapidly! ), one thing puzzles me...

...the whole point of the new-style cable is that the PVC covering is tougher, more heat-resistant, and thinner. It's thinner so that it can lose heat quicker, and therefore carry more current - but then it gets bundled up in a loom, which cancels that out!

It's a puzzle - but I'm not planning to lose sleep over it.

Back to the original question!

If using 'traditional' cable (normal thickness of insulation), the following ratings have been suggested:

0.30/14 (14 strands of 0.30mm wire) for the low-current stuff - sidelights, indicators, connections to the low-current side of relays.
0.30/28 (28 strands...) for high-current use - headlights, horn, fan, etc.

There's also a cable that I think is around 0.30/60, for the connection between the alternator and the battery - often doubled up for extra capacity.

Does this sound reasonable, Steve?

cheers,

David

David, yes it sound pretty reasonable a defintion as ive heard. As reguards the bundling of electric cabling in cars you are right but remember that it is all done by a university graduate who has never in his life worked on a car in a profesional maner, so you end up with something that works and as a rule these days works very well --- But have you every tried changing a front side light bulb on a new rover 75, or changing headlamp bulb on a new type beetle that done lots of miles. and ICME recons that on some cars you can change a wheel bearing in 6 minutes!


one day I will meet one of these new car designer types

Im sorry that this thread has gotten the way it has over a simple naming misunderstanding, but there ya go - and I learnt something too!

Cable ratings ARE confusing. When I checked today for 1mm cable, in the RS catalog, I got THREE different ratings! 6a, 10a and 17a!

I have seen the thin stuff on cars and it obviously works. It makes me a little suspicious tho - i'd rather have nice thick insulation.

The PVC covering on (some if not all) cables is radiation treated to make it harder and tougher. So I am told. (In case anyone else says otherwise!). Perhaps the auto cable is the same?


Now, you's think, using logic, that tri-rated cable would have a thinner wall to help it cool.

Not the stuff I have seen! It has a wall thickness thats pretty substantial - moreso than the 6a stuff!

I basically used two types on my car.

1mm for 'general' things like runs to individual lights, panel wiring, etc. I used (I think) 1.5mm approx with a rating a shade over 20a for other things, such as the main feeds from the fuses to the light switch, abs pump, fuel pump (efi), horn, and the like.

This was all Tri rated cable, having multiple approvals and a 3x in most cases power capability over the std cable Pleases everyone I hope

I dont recall any of my fuses being over 20A.

Then there is wire colour. If you look at the pics of my car, its all yellow. When I worked at a company that did MOD work, it was pink! All the wiring in a C130 herc I could see exposed was white I think (scutter?) In my experience of industrial machinery, there tends to be standard colours for things like mains wire, + power rails and ground rails. Low voltage control wiring (24vdc) tends to be all in one colour. So you get a whole load of cables one colour. There isnt a lot of colour combos to make every wire unique, so its normal to number the ends. You can get cable marker kits, or 'wrap around' cloth sticky numbers, that let you number each wire uniquely. So my car has a whole lot of yellow wires with numbers at each end so I know where they go. I also cheated by putting masking tape with a name of where it went or what it was for. This is removed after finsihing.

2 cable sizes with markers worked for me.


As far as the cable from the alternator is concerned, that can carry a lot! On my XJS the alternator was rated at 130 amps!

I would suggest that you take a visit to a scrappy and liberate a ready made wire from a car. A mk3 granada has a wire from the alternator to the battery thats a good 4 foot long. Why go to the hassle of buying new when a bit of white spirit makes it look new? Its hard to make off those high current ends without a proper tool. I think even a std ford has a 70a+ alternator.



"0.30/14 (14 strands of 0.30mm wire) for the low-current stuff - sidelights, indicators, connections to the low-current side of relays."

Thats about 9a cable. Each 5w bulb consumes less than half an amp, and a 21w bulb just under 2 amps. So thats fine - but keep fuses 10a max on those lines.


"0.30/28 (28 strands...) for high-current use - headlights, horn, fan, etc."

thats 18 amps approx.


your choices are just about the same as mine! Keep fuses 20a or less on these lines.


When you wire up the lights - especially headlights - try and use independent fuses - like have the dipped on one line, and the mains fused from another. If all the lights go it it could be hairy! Its also a good idea to have 2 fuses to the back - one for a lhs sidelight and another for rhs and numberplate - makes sure there is at least some light at the rear if a single fuse fails!

I also used two 5a fuses under the dash to fuse the dial lights, and to provide an 'always on' (when ignition is on) supply for the panel indicators (oil, etc.)

My system needed 18 fuses - but if you have non efi and non abs that puts it back to 16.

If you are interested I could get post what I used and what the ratings were.


Hope that helped David.



ATB

Steve.


Perhaps one day I can write up electrics for my site - with decent drgs - try to do a page a week but there isnt always time!

quote:

---

Originally posted by stephen_gusterson


Hope that helped David.

---

Hello All,

Some comments wich may be to some help?

PVC, most common insulation on automotive cables, are good for use in aprox -30 to +100 degC. Some qualities may stand for aprox 110 degC, but not more.
The "newer" thin wall insulation types were developed to save space, and the PVC quality is normally a bit better than the older "thicker" cables, but temperature range is the same.
The current rating is the same independant of the insulation thickness in the automotive industy.

The fuses are ment to protect the cables/installation if/when a short circuit appears.

Guide for a robust design:
5A fuse protects 0.75mm cable, 7.5A fuse for 1mm, 10A fuse for 1.5mm, 20A fuse for 2.5m and a 30A fuse protects 6mm cables.

Design the circuits so than the fuses in normall use is exposed to max 80% of their ratings.

Unfused cables:
I would go for 16mm cable between battery and starter, and 10mm between starter and alternator.

All the rest depending on load.

I hope this can be to some help.

Regards
/Hasse

Hasse,

That all looks very sensible.

Thanks,

David