What amperage on armoured cable

[Erich]

Hi All,

I'm converting my Ulster Rep from 12 volt to 6 volt. What amperage wiring should I use for the various components? I've seen suggestions of 16 amp or 8 amp, but I seem to recall that 6 volt requires heavier gauge wire. Is that correct?

Erich in Mukilteo

[Bryan]

See below, old packard chart for cable size. Yes the cables need to be bigger for 6v as you will de drawing twice the current.
   

[Chris KC]

Eric, for what it's worth, I'll attach below a table I made when re-wiring my Ulster rep.

This was scribbled on the back of a metaphorical envelope, it's not wired as standard, and I'm not 100% sure these are the sizes I ended up with (don't take it as 'gospel'); but it may help as a guide.

My advice is use the biggest wires you can find which will fit through your grommets and into end connectors - the more copper there is (width-wise), the less resistance. You might find it worthwhile to buy a small sample of each size from your supplier first so you can do the arithmetic or test fit.

Don't rely on earth return through bodywork - wherever possible arrange an earth cable back to battery.

Braided or armoured cable looks much prettier.

FWIW, some of the wiring I removed (typical stuff Halfords sell for modern cars) had melted its insulation (on 6V) & was a hair's breath from disaster.

Best of luck!


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[MartinH]

Chris,

Something wrong with your figures. Your headlamp cables using 14/0.012 are awfully skinny, less than 0.002mm2 in CSA . A typical 1mm2 CSA cable as you have for the tail lights is 14/0.3 and is good for 8A. For headlights with 35w bulbs and a good safety margin you'd be looking for 28/0.3 which is 2mm CSA and good for 17A.

I would recommend using a reputable cable supplier like Autosparks. Their website has all their cables listed with safe current ratings

[Chris KC]

Thanks for pointing that out Martin - I think what we have here is a case of mixed units (I did say it was "fag-packet"!)
That would be 0.012" which is about the same as 0.3mm - I used the same wire for both. 
Rather than confuse more people I'll update that in the table.

["Slack Alice" Simon]

If possible, earth returns on everything.

Remember, the earth may be carrying the same current as the feed, so it needs to be the appropriat spec.

I look at the current capacity quoted by the suppliers, and add some.


Eg:  35 watt headlamp bulb on 6 volts need at least : 35 divided by 6:   call it 6 amps. 

If there is a cable that will fit, rated at 10, I would use that at the very least.


For the feeder from the battery to the ignition switch - add up all the possible amps, and make sure that cable is rated properly.


If going from 12 to 6, the current capability of your starter cable needs to be checked and upgraded if necessary - doubled, if the previous owner installed it "down to the specification".

[Erich]

Hi All, I'm looking at armoured cable from the Complete Automobilist. They have amps listed but not diameters. 6 amp, 8 amp, I think 16 amp and 27 amp. It sounds as if I use the 8 amp I'll be OK for most things, inlcuding head lamps, correct? Otherwise, I could go to 16 amp for extra safety or is that overkill?

Erich in Mukilteo

[MartinH]

It all depends on what you are using for headlamp bulbs, incandescent, frugal leds, or power hungry halogens. Take your bulb wattage, divide by 6 to get amps and then add at least 50 percent for safety margin.

[Chris KC]

I probably should have said my car is pretty much "standard" Austin Seven spec i.e. no LED's etc. - I have yet to encounter any issues using the specs above.

For reference: 

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(I got these figures from the wholesaler, you will find slight variations quoted).