K8096

what wire gauge to use?

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In looking at old wiring diagrams from the 1920's & 30's, they never say what gauge wire is used in each application. How do you know what gauge to use? For example, I want to replace my coil to distributor wire for a 6 volt negative ground car. What gauge should that be?

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Guest imported_JPIndusi

I would use 14 gauge for the coil to distributor wire on a 6 volt car.

You may want to contact Harnesses Unlimited or Rhode Island Wiring Service for more information and/or a complete wiring harness for your car.

Joe

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Most times #12 or #14 gage (copper stranded) will be sufficient however you should go by the fuse size to determine the wire gage. Wire ampere capacities depend on jacket insulation and degree rating. For vehicle wiring I won't use anything less then #14. Based on copper wiring a safe general rule of thumb is:

#18 wire is 9 amps maximum

#14 wire is 15 amps maximum

#12 wire is 20 amps maximum

#10 wire is 30 amps maximum

#8 wire is 40 amps maximum

#6 wire is 55 amps maximum

#4 wire is 70 amps maximum

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I have never seen anything lighter than #14 in a six-volt car, and my hands-on experience takes me back to my Dad's 1930 Chevy.

I like #12 for most lighting and long runs on my six-volt stuff.

A good check is to apply a voltmeter to both ends of the wire in question, while energized: a voltage reading of more than 1/10 volt indicates too much internal resistance in the wire either due to corrosion or too small a wire being used.

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And always keep in mind that a 6 volt system when running will read approximately 7.2 to 7.9 volts while a 12 volt system will read 13.3 to 13.9 volts if all is operating correctly. Amps is amps no matter what the voltage and that is what the wire needs to be protected for. 6 volts systems always have heavier cable as the lower the voltage the more resistance and larger cabling compensates for this. Look no further then the battery cable sizes between a 6 and 12 volt system.

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It's not the lower the voltage the higher the resistance, the problem is with 6V systems is that your 35W headlights will draw twice as much current as on a 12v system. Ie. 70W's (both headlights) is 70W/6V=11.66A vers 70W/12V=5.83A. (P=I X E) Now if you use a smaller guage wire the resistance per foot of wire increases reducing the voltage you would get at the headlights making them dimmer as you may have 7.5 volts in the battery but mAy get 6V at the headlight due to the voltage drop in the wire. If you check some books it will give you a resistance of wire per foot per guage.

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You are correct. In my haste I made this error. A rule of thumb regarding acceptable maximum voltage drop is approximately 5% of the source voltage. At 12 volts no accessory, etc should read less then 11.40 volts. Amperes are still amperes and that is what the wire needs sized to.

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Go to "vintagehotrods.net" on your address bar.

Go down the left side to "wire & fuses"

You will get two very nice charts that tell you what fuse to use for each item (RADIO) etc. The other chart tells you what size wire to use for each item such as "PANEL LITES", "BRAKE LITES"etc.

You can get reproduction wire at www.magnetoparts.com/wire.htm

Good luck with your project. Dave

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Take a look at an old Dykes manual. I remember something about what gauge to use for which connection in a '24 Dykes, not completely sure.

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On 1/8/2005 at 11:47 AM, 28&610lds said:

Go to "vintagehotrods.net" on your address bar.

Go down the left side to "wire & fuses"

You will get two very nice charts that tell you what fuse to use for each item (RADIO) etc. The other chart tells you what size wire to use for each item such as "PANEL LITES", "BRAKE LITES"etc.

You can get reproduction wire at www.magnetoparts.com/wire.htm

Good luck with your project. Dave

I went to " vintagehotrods.net" there all I saw was a main page directing me to other sites- directing me to other sites, could you be more precise?

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Ron Green's listing above is good for 6 volt systems.

 

Just figure out the amperage draw of what your wiring to/from. In a single wire system (chassis is the ground path), most auto wire lengths - power to wire ground - are usually so short the voltage drop per length is not critical.  But when in doubt, go another gauge thicker to be safe. The added expense for the next heavier gauge wire is far cheaper than damage from an electrical fire !!!!!

 

I've never seen any wires lighter than 14 gauge wire used in a 6 volt system.

 

For 12 volt systems, you can go one number gauge higher than with 6 volt.

 

For a 6 volt starters use  nothing less than 00 gauge.

 

Paul

Edited by PFitz (see edit history)
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1 hour ago, PFitz said:

For 12 volt systems, you can go one number gauge higher than with 6 volt.

 

Good rule of thumb for all the even gauges, like what you can buy in automotive wire.

 

To confuse you, wire comes in all number sizes, though typically the odd numbers are just in enameled wire, like transformer and motor winding applications. The rule of thumb is current capacity doubles for every three wire sizes counting the odds. So, a awg 12 carries twice the current of awg 15.  This is where PFitz's rule of thumb comes from, and it is a good one, with extra capacity built in.😉

 

I do have a roll of test  lead wire that is 17 awg and very flexible. I use it for points leads on 12 volt distributors where the wire is always flexing due to vacuum advance moving the points plate (or whole distributor you Chevy 235 people). Too small for 6 volt ignition current draw.

 

 

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Note that the chart is based on a "maximum voltage loss of 1/2v". You don't want anything close to that much loss in a headlight circuit or a charging circuit. It cant hurt to go a little bigger.

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Jeff, I did not see earlier, but you responded to a 14 year old thread. The links change over the years. People forget to renew or pass away.

 

But, you have some good advice so far, and some charts that will be in this thread until something happens to picture server later on.

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The chart provided is helpful:

 

However we should add  #16 gauge wire.

 

It is 12 amps maximum. It is the most common form of extension cord, and is a fire risk when you fire up your 1500 watt heater.

You should ask  why the industry uses it in power strips that are rated for 15 amps or 1440 watts. Do yourself a favor, and only 12 gauge extension cords. 

 

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For voltage & current requirements for wire, think current is current regardless of the voltage.  Size and material (copper, aluminum, etc) of the wire is the limiting factor for the wire to carry the current.  

 

The insulation type is the determined by the expected voltage that the wire is going to carry.  Example is the difference between headlight wire and solid copper spark plug wire.  I have not checked but probably about the same wire size, but the insulation is different for the sparkplug wire because the spark plug wire would be carrying a 20,000 - 35,000 volts and regular headlight wire which carries 6 or 12 volts would probably arc through the insulation with the high voltage.

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I have almost the same problem just a different question.- Is it safe to do most of the wiring for a 6 volt in 14 gauge ? I have the diagram- and again it doesn't say the gauge and when I look at most the bulbs they all say what "volt" . But only a few mention what amp. - So a mechanic said best and safest thing to do was start with 14 ga. for most and then go bigger. He said most 12 volts use 22-16 and that's way to small of a gauge. ( If I use to small of a gauge it could catch fire ) or a person can use a 12 volt battery with 6 volt wiring- but can't use a 6 volt battery with 12 volt wiring. I ask all of this because I thought about converting my 6 to a 12. and if I ever sell the car a person could go back to a 6- if they want to make it original

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14 gauge is used for most 6 volt low load circuits, such as lights.  But, there are other circuits that require heavier gauge, such as the wire from the generator, the feed to an ammeter and fuse blocks.

 

In stead of playing guess  the amp load and gauge needed, have you tried contacting Rhode Island Wiring Service ?  They make duplicates of the original harnesses for most makes/models of car. And the correct wire gauge and terminal end sizes for the load on  each circuit has already been duplicated from the originals, including the color coding to match the original wiring diagrams where known. Then they cover it with the correct woven loom like the originals and include diagrams of what and where each wire/terminal gets connected.

 

Paul

Edited by PFitz (see edit history)

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Yes I have and I have even visited their place. Excellent people.  Problem is when I did it the economy went into the toilet and I couldn't afford them and now that I'm retired, Soc.Sec. is even worse pay and they don't have a plan to buy sections at a time. Just found a new problem- Although wiring really isn't a big deal- these are very simple cars. I began working off of a standard model 1948 8cyl. Pont. diagram. Could figure out what was missing and was having trouble finding the area for the "turn signals" my car came with.  Turn signals were only added for the "deluxe" models so they are not IN the diagram. In the "standard"diagram they are called "   Stop lamps".  I did find my diagram for a deluxe 6 cyl. and it has the diagram area for "TURN" signal and STOP lamps. Be careful when reading a diagram.and double check. 

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