JD;
It's a good idea to size your wire based on how much current is going to be
required in that wire. The rule of thumb is to size the wire large enough so
that it has a maximum of 0.5 volt drop (in a 12V system) at its maximum load
current.
#12 copper wire has a resistance of 1.88 ohms per 1000 ft @ 20C so every
foot of the wire adds 0.00188 ohms of resistance in series with the load. In
the case of a 20A Weldon fuel pump at the end of a 10 foot wire, the voltage
drop would be 10 ft X 0.00188 ohms/ft X 20A = 0.36 volts. So, assuming no
significant resistance in the ground return you would be fine using #12.
Regards, Neil Tucson, AZ
-----Original Message-----
From: James Tone [mailto:gmc6power@earthlink.net]
Sent: Monday, October 29, 2007 3:16 PM
To: neil@dbelltech.com; 'Dick J'; 'lsr list autox'
Subject: RE: [Land-speed] Wiring and Fuses
Whether you stated or not that still is the size wires that should be
used....CB size is 10% over the continuous rating capacity of the wire. DC
also loses voltage at a higher rate than AC with distance. Race vehicle
should make no difference. I use #12 for fuel pumps and water pumps even
though I knopw that is twice the required size for the current of the
component. Whether wise or not I don't use many fuses.
>
>JD;
>
>NO, these are CB ratings for various wire sizes.
>
>Note that I said "These ratings are only for CB protection of the wiring
>itself, not how big a wire you should use for a particular load current."
>
>Regards, Neil Tucson, AZ
>Subject: Re: [Land-speed] Wiring and Fuses
>
>These numbers are for continuous current. Most cars today have 100 amp or
>higher alternators and you never see #4 wire on any of them. You are lucky
>to see a #10. This is not telling to use smaller wire this is just an
>observation. I use a #8 on my alternator and #1 or 1/0 for batterey cables.
>That was the old sizes for 6 volt cars. Use the same size as your battery
>cable to ground the engine to the frame. If you use a an ignition box and
>mount it on lord or rubber mounts be sure to put an extra chassis ground on
>it even if one of the wires comimg out of it goes to a ground...Good Luck
>
>Also If you are smart you will not use crimped fittings. Buy the
>noninsulated ones if possible and solder all ends. (you can remove the
>insulation) Apply numbered or colored heat shrink over each solder joint
>>
>> Copper Wire Size Circuit Breaker (amps)
>>
>> #22 & #20 5
>> #18 10
>> #16 15
>> #14 20
>> #12 25 or 30
>> #10 35 or 40
>> #8 50
>> #6 80
>> #4 100
>> #2 125
>>
>> Bear in mind that wire temperature will be higher if it is enclosed or
>> bundled into a cable. These ratings are only for CB protection of the
>> wiring
>> itself, not how big a wire you should use for a particular load current.
>>
>> I hope this may be helpful.
>>
>> Regards, Neil Tucson, AZ
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