Just about to start hacking the zx9 loom apart and extending/shorting it where needed. What sort of rating/size wire should i be using. Not worried about lighting at the moment, just want to get the egine running

Handy page about wiring:

http://home.clear.net.nz/pages/phil.bradshaw/car_wiring.htm

BoL,

Pete

The wire thickness depends on the curent that flows throw it (not the voltage. the voltage governs the insulator thickness).
I can only give rating on house hold wiring hope it helps.
these are for tri rated cable.
1mm - 19A
1.5mm - 25A
2.5mm - 34A
4mm - 46A
6mm - 59A
10mm - 81A
16mm - 109A

I would use tri rated cable because it is nice and flexible and more inportant it can take 90 C beffor the insulator starts to get damaged (insted of 70 C).
quick point thow for exsample if you have a cable is carying 18 A and it is in a big group of cables go for 1.5mm insted of 1mm because of somthing called grouping factor so if there are lots of cables in a group and it is close to the limit go up a size.
same with engine bay if it run in a place that is going to get hot and it's geting close to the limit go up a size.
Then agane if power is only on for a few seconds and then turnd off and there is a resanable amount of time beffor it is put back on may be go down a size eg. 20A go for a 1 mm cable.
good look with the loom haven't started mine yet

Good link pbura
these ratings are for normal 70 c pvc not tri rated i think ?
(posted when i was typing )

thinking on 70 c pvc is probably ok because of the short time that thing are swiched on (dose not have time for the heat to build up).
save your self some money get normal 70 c pvc.
I would make shore that you get stranded cores (not one solid core) so it bends easy and is less likey to brake

thinking on 16mm dose sound a bit small for your main 100A

Err, I know (hopefully) that it has only been used as an example, but I wouldnt advise anybody to use household cable in vehicle wiring.....

To put it simply, the higher the voltage, the less work that leccy cables have to do. Obviously there is a big difference between 12v and 240 volts....

what cable do you think i should use for my loom then?

dose pvc react with petrol and the like
if not there is no reason not to use normal 70 c pvc insulated.
as i said beffor the voltage is only the the insulator rating. there is no difference between dc and ac because ac is mesured at a rms value what is the equivalent dc value.
if a cable of the same crossection can take more current it is because the insulator can take more heat (the more current gose throw the wire the hotter it gets)
have a look at wiring regs bs 7671 if you can get hold of one ( it's a reference book every electrician should have one)
if there is a wiring regs for cars i would like to take a look at it if eney one has one ?

I was going to use the wires from the donor loom. Not just because Im tight but I should be able to extend the wiring with the correct colour codes, and I presumed that it must be up to the job since it was doing it before.

Ooops, sorry, wrong thread.

Thought it said "wife rating" and got all excited.


I'll get my coat

240 volt 1.5mm cable has a rating of 25 amps.

Ohms law states that volts = amps x ohms.

So, 240 (volts) divided by 25 (amps) means that this wire is capable of running a component with a resistance of 9 ohms.

Now to put that into perspective in a 12 volt system. Using Ohms law above, if we divide 12 volts by 9 ohms, we find that we only need a wire with a current rating of 1.3 amps. All very simplified, but shows to highlight whats going on.....

So in reverse, for an 12 volt electric fan with a current drain of 15 amps, in simple theory you would need 240 volt cable rated at 300 amps.....

whenever ive done electrical stuff on cars (mostly helping me mates do mods on their cars, bloody boy racers ) ive used equipment wire, i think it is 1mm, cant remember the ratings, but will post later cos im on me back out to the shed now so will ave a look



Russ..

yes stu this is right but it is a mater of power.
for example power (watts)= volts x amps
so for a 16watt fan current would be for 12 volt would be
amps = watts/volts
so
amps = 16w/12A
so
amps = 1.33A
lets try that with 240v
amps = watts / volts
so
amps = 16w/240v
so
amps = 0.067A
there for on 240v for the same power you would need a smaller cable
equipment wire is normaly 70 c pvc wire

when i say 70 c wire i meen 70 degrees c
tri rated is 85 c to 95 depending on who makes it
70 c is the temp the insulator can get up to befor it starts to brake down

RS do cables tayor made for the job.

www.rs-components.co.uk

thay give you all the info you need (graph curent against temp)

thay have some nice green wire this will make a good looking loom with some cable ties

yep, the equipment wire i use is 1.5kv rms 6A at 70 c. ive never had a problem with it. i mostly just use it cos i bought a few 100m reels of varying colours so i need to use unless its gonna go in me will for the grand kids (im 23 btw)

quote:

---

Originally posted by rell
yes stu this is right but it is a mater of power.
for example power (watts)= volts x amps
so for a 16watt fan current would be for 12 volt would be
amps = watts/volts
so
amps = 16w/12A
so
amps = 1.33A
lets try that with 240v
amps = watts / volts
so
amps = 16w/240v
so
amps = 0.067A
there for on 240v for the same power you would need a smaller cable
equipment wire is normaly 70 c pvc wire

when i say 70 c wire i meen 70 degrees c
tri rated is 85 c to 95 depending on who makes it
70 c is the temp the insulator can get up to befor it starts to brake down

---

I don't see where you get 300A from?

a 300A cable at 240v will deliver 72000 watts
to get this current on 240 you would
need 0.8 ohms load for this current

and at 12v it deliver 3600 watts
on 12v you would need a load of 0.04 ohms

a 300A (thats a 240mm cable) will take 300A at 12v or 240v the only thing that changes is the insulation rating(the thickness of the pvc).

I see where y sliped up.
you put 300A insted of 300 watts
power = Volts X current

power = 12 X 25

power = 300 watts

but still cables have a current rating and a voltage rating not a power rating.

I think i will be useing this cable.
ACW High Temperature Engine Harness Wiring


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Sold in reels of 100m
stock no. price per reel
1-7 8-15
0·5mm2 Black 369-4771 £23.79 £21.78
Red 369-4787 £23.79 £21.78
Green 369-4793 £23.79 £21.78
White 369-4800 £23.79 £21.78
(September 2003 Catalogue page 1-261)

Sold in reels of 100m
stock no. price per reel
1-7 8-15
1·0mm2 Black 369-4816 £32.11 £29.39
Red 369-4822 £32.11 £29.39
Green 369-4838 £32.11 £29.39
White 369-4844 £32.11 £29.39
(September 2003 Catalogue page 1-261)

Sold in reels of 100m
stock no. price per reel
1-7 8-15
1·5mm2 Black 369-4850 £39.73 £36.36
Red 369-4866 £39.73 £36.36
Green 369-4872 £39.73 £36.36
White 369-4894 £39.73 £36.36
(September 2003 Catalogue page 1-261)

Sold in reels of 100m
stock no. price per reel
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2·5mm2 Black 369-4901 £53.11 £48.60
Red 369-4917 £53.11 £48.60
Green 369-4923 £53.11 £48.60
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(September 2003 Catalogue page 1-261)







ACW wire is a composite construction with a tough radiation cross-linked fluoropolymer outer layer. This outer layer is bonded to a radiation cross-linked polyolefin.
Excellent fluid resistance, designed to withstand attack from a range of automotive fluids, including oil, brake fluid, antifreeze and fuels

Designed to function in the hot engine compartment environment

Excellent mechanical strength

Ideal for automotive wire handling

ETFE material performance at reduced cost

Smaller, lighter and more flexible

High level of compatibility with other automotive materials

Reel length = 100m


Note:This is a recommended replacement for Type 62™ automotive Wire.
technical specification

Wire Size CSA Conductor Primary Max. Cond.
(mm2) Strandings Wire Resist @ 20°C
(mm) O.D. (mm) (Ω/Km)
0·50 19/0·18 1·50 37·10
1·00 19/0·23 2·00 18·50
1·50 37/0·22 2·30 12·70
2·50 37/0·28 2·85 7·60



technical specification

Method Typical Value
Operating temp. ISO 6722 150°C (3000hrs)
Voltage rating 50V
Thermal overload ISO 6722 200°C 6hrs
High temp pressure test ISO 6722/WD 150°C 4hrs 1kVa.c. rms
Cold bend ISO 6722 -40°C
Flammability ISO 6722 45° Flame
Hot shrinkage ISO 6722 150°C <2%
Oil resistance ISO 6722 90°C <1% swell
Fuel resistance ISO 6722 23°C <1% swell








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temp data on attachment

Insted of using different coloured wires use numbers that clip on to the wire

i myself will simply use new 12v wire, read the rating and pick an approproate size, and hence avoid the headache associated with equations!

regular size house hold wire that takes 13amps is actually quite thin as it obviously has 3 wires inside, car wire only has the one. As already pointed, out due to the difference in volts an identical wire running at 12v will supply one twentieth the power of a 240v wire if the amps were the same. So if you crank it back up to get the same power you have 20 times the current.

so which ever origin of wire you use, the power drain of the appliance will be the same and the current will be the same, as the volts will still be 12. The only problem with household wire is that because it is assumed it will be running at 240 volts, a given max current (say 13 amps) will result in max power of around 3.25kW. If you try providing 3.25kW at 12 volts it will have a current of 260amps. Bosche.

Is wire rated in amps or watts? I would have imagined it would be in amps, in which case it is a moot point cos the max amps is the same whatever the volts, it just means that less power can be supplied over all due to the lower volts.

Are both these equations correct? im just quoting those above:

volts= amps x ohms
P=VA

if so power = amps^2 x ohms,

so in stus example above the 240v wire rated at 300amps would be capable of supplying 22MW.

As rell says, voltage only changes the thickness of the insulation.


I must at this point remind everyone that i know nothing about electrics, only A level physics years ago, so please forgive me if im talking bollocks. made sense when i wrote it...

Joel,

You not talking rubbish, you just don't need to worry about resitance as generally any car load is quoted as a power rating, so it's just power rating/ 12V = steady state current.

I've just started designing the wiring loom and have come up with the following requirements. I am going to use plenty of fuses to help with identification of problems so will have the following circuits...

Stop/Tail lights 2x21W + 2x5W current = 4.333 Amps.
Side Lights 14W, current = 1.2 A
Fog Light/ Reversing light 2 x 21W current = 3.5 Amps
Indicators 94W current= 7.83 Amps
Headlamps 240W current = 20 Amps

I've yet to rate other items like the horn and the ignition/charging circuits.

The values above don't allow for warning lights etc, but I was planning to group them all together and use 25Amp cable for everything except the headlights (use 39Amp).

Andrew

house hold wire also tends to be 'stiffer' than auto wire and can run the risk of stress induced breaking in an automotive environment.

Beet me to it badger just about to say the same thing.
and yes cable has a current rating not watts
don't no where you get 22MW from you corectly said

power = amps^2 X ohms
so there for
power = (300 X 300) X 0.8

power = 90K X 0.8

power = 72KW

for a 240V supply to deliver 300A it must have a resistance 0.8 ohms

V = I X R
there for
R = V / I

R = 240 / 300

R = 0.8 ohms

but it's all geting technical againe keep it symple as badger says work the curent out and look on the chart for the right size wire.
do not use house hold wire no one has advised you to use it on this post? i think people think when i said 70 c cable thay thort i ment twin and eirth the flat gray stuff or flex what you wire plugs up with not the case i ment get a roll of single wire that is stranded so it is flexable.

quote:

---

Originally posted by JoelP
so in stus example above the 240v wire rated at 300amps would be capable of supplying 22MW.

---

i did an experiment put some pvc cable in jery can with some petrol in this morning
it feels a bit tacky on the serface not good just put some in oil to see what it will do?
had a look in the maplin book there is only normal equipment cable. unlike rs which has cable specialy made for automotive industry. as put on my previous post.

*backs arse in hedge slightly*
Yes, in retrospect my '300 amp' example is flawed, as it is assuming that both a 12 volt and 240 system will be driving a component of 0.8 ohm resistance, where as Rell correctly states the power (watts)is going to be totally different at the receiving end of the cable. But the point is still the same, heavier duty cable is needed for lower voltage systems driving components that make the same power.

Cheers, Stu.

A very short proposal:
Go for 1.5 mm2 wires for everything exept 10mm2 from starter to alternator and 16-25mm2 from starter to battery.
Use maximum 20A fuse to 1.5mm2 wire. This will in worst case cause a temperature rise of 30 degC in the wire ( on top of ambient temperature) just before the fuse blows( about 25-28A).
Normaly PVC works fine with small amounts of everything chemical present in a car exept for brake fluid.
Avoid temperatures above +90 degC.
Regards
/Hasse

sounds about right to me.

quote:

---

Originally posted by rell
yes stu this is right but it is a mater of power.
for example power (watts)= volts x amps
so for a 16watt fan current would be for 12 volt would be
amps = watts/volts
so
amps = 16w/12A
so
amps = 1.33A
lets try that with 240v
amps = watts / volts
so
amps = 16w/240v
so
amps = 0.067A
there for on 240v for the same power you would need a smaller cable
equipment wire is normaly 70 c pvc wire

when i say 70 c wire i meen 70 degrees c
tri rated is 85 c to 95 depending on who makes it
70 c is the temp the insulator can get up to befor it starts to brake down

---

i think your geting confused with power factor on your ac

P = V X I X pf

the power factor is the angle the curent leads or lags the voltage depending on wether the load is inductive or capasitive on inductive loads the curent lags and lead on capasitive.

the power factor is the cos of the angle that the curent lags or leads.

don't forget the voltage is mesured at rms values

i was gonna mention RMS myself but didnt wanna argue with someone who knows more than me!