Wiring 101

Revision: 01/02/2003

Introduction:

I plan to add electrical accessories to my GL1800 and NOT being an electrical authority I had to obtain some knowledge of wiring and fuses. With the help of the Internet and fellow Wingers, I created this wiring reference guide to assist me with all my electrical projects. The following are some of the resources that I used to create this quick reference guide.

Wire:

http://www.rallylights.com/other/wiring.htm

Fuse:

http://www.zenithair.com/kit-data/ra/electric1.html

Things to Conceder:

  1. Use a large enough wire so there is no voltage drop. You want whatever that is wired to operate at top efficiency.
  2. Maintain an adequate safety margin. We don’t want to melt any wires do we?
     

Determine the Current Required:

Radios, CD players, and things like that are rated in Amps.
Lighting equipment is mostly rated in Watts.

To calculate for amps:

  • Current in Amps = Power in Watts/Voltage in Volts
  • Current in Amps = Voltage in Volts/Resistance in Ohms
  • Current in Amps = The Square Root of Power in Watts/Resistance in Ohms

Once  you know the amps the devise requires you can determine the wire and fuse size to use.

 

Example:

Calculate for a 100-Watt Driving Light. The power required is 100 Watts and the voltage is 12 Volts. The following formula is used.

  • Current in Amps = Power in Watts/Voltage in Volts
  • 8.33 Amps=100 Watts/12 Volts
  • 8.33= 100/12
  •  The current required is 8.33 amps
     
    NOTE: Actually, it's somewhat less because the rated output of a lamp is figured at 13.5 volts, not 12 volts. If the Alternator is working correctly its output is 13.5 volts. Wire size for lighting is more critical than for other applications. Calculate to the high side when sizing wire for lighting.

The Fuse:

It is important to selecting the right size fuse or circuit breaker for the size wire you will use to power the electronic component. The fuse or circuit breaker should trip before the wire gets hot enough to begin smoking.

The following chart is found in FAA Advisory Circular 4313 and shows the comparison between wire size and circuit protection.

Wire Gauge Circuit Breaker
Amps
Fuse Amps
22 5 5
20 7.5 5
18 10 10
16 15 10
14 20 15
12 25/30 20
10 35/40 30
8 50 50

 

What happens if the wrong fuse or circuit breaker is used?

Example:

If a 10-amp fuse is used in a circuit connected by a 22-gauge wire, and an electrical fault occurs, then the 22-gauge wire well start to burn before the fuse breaks.

NOTE:

If the fuse (circuit protection) is too small for the wire size then the fuse will break requiring you to replace it even if there are no real problems.

The Wire Gauge Size:

Maximum length in feet for car wiring

Wire Gauge Current Load in Amps @ 12 Volts DC
4 A 6 A 8 A 10 A 12 A 15 A 20 A 50 A
20 AWG 26' 17' 13'          
18 AWG 37' 25' 18' 15' 12'      
16 AWG 56' 37' 28' 22' 18' 14'    
14 AWG 90' 60' 45' 36' 30' 24' 18'  
12 AWG 143' 95' 71' 57' 47' 38' 28'  
10 AWG 227' 151' 113' 90' 75' 60' 45'  
8 AWG 363' 241' 181' 145' 120' 96' 72' 29'
6 AWG 585' 390' 292' 234' 194' 155' 117' 46'
4 AWG 925' 616' 462' 370' 307' 246' 185' 74'
2 AWG 1515' 1009' 757' 606' 503' 403' 303' 121'
1 AWG 1923' 1280' 961' 769' 638' 511' 384' 153'
0 AWG 2427' 1616' 1213' 970' 805' 645' 485' 194'

 

How to use the Chart:

1. Calculate the current load that the component requires.

2. Select the next highest amp on the top row.

3. Go down that column until you find the length you need to run the wire.

4. The wire gauge required is shown in the far left column.

The maximum lengths are based on a 1/2-volt drop over the indicated length. To be safe, always choose one wire size larger than you need for the required current carrying capacity and length.
 
Example: You have calculated a 10 amps load, over a length of 17 feet. The chart shows that 16-gauge wire as suitable. Choose 14-gauge wire to allow for an adequate margin for safety.