What size wire to use when wireing stuff on your hotrod

There are a couple factors to consider when running a wire for something. Ignoring this will most definatly lead to blown fuses, smoked wires and more.

The problem is ohlms law. It is a mathamatical equation between Volts Amps and Resistance.
If you use too small of wire (resistance), the voltage drops at the appliance, say the headlight. The amperage draw of the headlight increases to compensate (its mathmatical). This melts wires, blows fuses and generally causes problems. Use a bigger wire, problem solved.

This resistance thing also applies to connections, rusty grounds, and corrosion on the copper wire itself. It must be clean ( on the surface of the wire) to carry the current without voltage drop.

Factors to consider

1. the amperage draw
2. the voltage (most likely 12v dc here at RRR)
3. the distance to the appliance AND back to the battery.

using the handy calculator linked below, you can make sure you use a wire big enough to do the job with out problems.

http://www.powerstream.com/Wire_Size.htm
fill in the blanks and press calculate. The idea is to have less than 10% voltage drop, 3% is better. If the voltage drop is too high, go back and change to a bigger wire gage.

Electrical things come with a measured amount of smoke in them. If you let the smoke out, you have to get another one.

Sparks are good and fire is our friend.

Please feel free to add to this. I am a rooky.

Good tip.
Like I said earlier, most people don't take into consideration amperage draw.

Thanks for posting the link.


Tracy

WIZEGUY said:

Good tip.
Like I said earlier, most people don't take into consideration amperage draw.

Thanks for posting the link.


Tracy

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Lots of people think electricity is black magic. Its not, but there are a few things to know.
I cant tell you how many times I have seen a car with major electrical problems because of a bad stereo instalation.

Relays are the best way to use high amp items like fans and fuel pumps. Ive wired many without them but nowadays Im using relays on both.

Whats a stereo?

SmallBlock Jimmy said:

Relays are the best way to use high amp items like fans and fuel pumps. Ive wired many without them but nowadays Im using relays on both.

Click to expand...

Good tip.
Relays are good to use, never wire your component straight through a toggle switch.


Tracy

SmallBlock Jimmy said:

Whats a stereo?

Click to expand...

lol


Tracy

I think a "stereo" is the burbly sound of exhaust with a healthy cam.
But why would you need to wire exhaust?

Inked Monkey said:

I think a "stereo" is the burbly sound of exhaust with a healthy cam.
But why would you need to wire exhaust?

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You only have to wire it long enough to get back to the shop for welding.

The stereo comes from sitting between both pipes.

SmallBlock Jimmy said:

Relays are the best way to use high amp items like fans and fuel pumps. Ive wired many without them but nowadays Im using relays on both.

Click to expand...

You must use relays when needed.
The same rules apply.
Use big enough wire.

You talk about voltage drop......actually voltage drop effect does not happen until you are at a length of 150 feet, then the drop is in a % of the load requirements. As far as a car wire goes, most instrument lights draw less then 1 amp. You can look at most car wire jobs from the factory and you will find #22 gage wire is the common size for 80% of the car needs.
Your alternator will be the largest general wire at #6 gage. The starter wire from the battery, and the ground wire are usually 1/0, current load of the starter will garner the actual size of the wire.

You must understand the total current load of each run, your head lights will be the second largest in current load factors of the standard electrical circuit.
If you install a high power stereo system, you will concider this a secondary main circuit, which is always wired seperate from the overall car circuitry system.
Understanding Ohms law in electrical calculations is no mystery and I reccommend that every car enthusiest should learn this simply math.
Current load and power consumption are critical, but also can be simply understood. Everything is figured in a series circuit or a parrallel circuit in the different runs. It is almost like wiring a fuse pannel to your house. I would believe many of you have done additions one time or another to your dwellings and had to learn how to do this. It is all based on the same principle. I could go on and teach everyone the basics, but it would be everyones' advantage if you went the library and picked up some basic automotive electrical books. They are free for three weeks at a time.

Good luck all,

Maximo

Relays are good for all the main accessories in the ride. Cooling fans, A/C and heat system, fuel pumps, head lights and dimming circuits, stereo systems.
Then you must do a good one line drawing of your whole ride and all the electrical goodies or simple setup. Get a completed listing table of everything in your circuits. Each circuit should ba able to handle more then one item in the line. Check your ratings of all items and add up the total wattage of everything, then you can figure the total current draw of each circuit.
Your Hayes or Chilton manuals actually are great lay outs for any build. They all have your diagrams layed out and the actual wire sizes for each combined circuit.

Good luck.

Maximo