Wiring question

[AndyD]

Hi,
Hope someone can advise on wiring size as I'm getting a bit confused.
It's for a XT250 which is 6v and I've only ever worked on 12v before.
The loom and attached wiring connections have been hacked about and various wires replaced, spliced, shortened and generally bodged so I'm looking at making up a full new loom as I'll also need to extend some wires where the PO cut and reconnected them.
From Googling around I believe that with 6v systems you need to increase the wire size due to increased amps - normally used 1mm wire on most parts of previous loom repairs on 12v bikes.
I'm not sure if I can simply go for 2mm for everything in the loom or if any wires need to be anything larger - nothing looks much different in the old loom but I don't really know enough to be sure.
Any advice very welcome before sitting down to work out the list of colours and cables needed.
Cheers,
Andy

[McCabe-Thiele (Ted)]

As I'm sure you are aware when you halve the voltage for a given Wattage bulb you double the current (Amps).
So for ease of comparison a 48 W bulb on 12 volt circuit would be a current of 4 amps.
A 48 W bulb on a 6 volt circuit would be a current of 8 amps.

I don't believe that you have to double the diameter of a cable as the increase is not a straight multiplication as the cable has a round profile so as the area doubles I don't believe the diameter does.


Many sites list the wiring specification accordingly plus better cable materials lower resistance.

[davidcumbria]

As diameter doubles area goes up by x 4. Diameter triples area goes up by x9. It is a true exponential relationship unlike the much overused phrase nowadays for ‘increases rapidly.’

 Conversley for the same power rating of 12v wire I reckon  a 6v wire will only need to be wider by  square root of two ie x1.4 not double.

[AndyD]

Thanks guys,
The main reason for jumping from 1mm to 2mm is simply because these are the two sizes I could see readily available in the umpteen colour / colour combinations needed.

I read some far too technical for me bits about wire sizes and came to the simplistic conclusion that using 2mm (rated at 25amp compared to the 1mm rated at 16amp) should be good for most circuits on the 6v system.

In one article on 6v bike wiring it pretty much seemed to say this but also noted that some parts of a loom may need to be different again but didn't explain which bits or to what extent. I guess it may relate to the magneto wiring but on the existing loom this appears to be the same thickness wire so I was a bit uncertain.

Bit more googling to do I guess.

Cheers,
Andy

[McCabe-Thiele (Ted)]

There is also 1.5 mm cable out there plus a choice of normal or thin walled insulation - also different copper contents.
Some of the cheaper cable is copper coated I believe.

[AndyD]

Thanks Ted,
I've generally bought cable from Bikers Toolbox in the past and they have the 1mm and 2mm thin walled wire in lots of colours - there's something like 17 different ones on the XT.
Haven't seen any 1.5mm ones in wide colour ranges - is there a source for these?

Cheers,
Andy

[McCabe-Thiele (Ted)]

I bought from ebay and Vehicle Wiring Products iirc at Ilkeston

[Aye Gee 1977]

Cables and flexes sizes are generally expressed as cross sectional area of the conductor so a 1mm wire is shorthand for one having a CSA of 1 mm sq.  Therefore the copper is proportional to the number i.e. 2mm is twice the size of 1mm.

Cable sizes on motorcycles are principally determined by voltage drop rather than absolute current carrying capability.  The way this works, a 6v system requires a conductor four times the CSA of a 12v to have an equal voltage drop.  Keeping the conductor size a bit sensible is the reason why the National Grid transmits a high voltages (e.g 275,000 volts) and steps it down locally for domestic use.

[BigAl (Alan)]

'volt-drop' on 6 volt motorcycles can be a problem as they age due to corroded wire/connectors/switch gear.  As the original post, assembling a new wire harness with 2mm cable, as to the original 1mm cable would help, as the resistance value per metre of 2mm cable is lower that 1mm cable.
Fitted a new wire harness (2mm cable) to my XL500s (6 volt system) as image a number of years ago...it did improve the lighting system.