Amps on AWG chart

Thread Starter

Boyd.Ako

Joined Dec 1, 2019
7
Anybody know where I can find a good chart that lists the of amps that that can run on a certain wire gauge? Optionally, also have an estimate of the resistance of the wire gauge to how long the wire is.

I've already tried googling it and not exactly the type of charts I'm looking for.

Scenario: What's the max amount of amps I can run on 16AWG that's approximately 15 feet long. I'm trying to run a hot wire from the engine bay of my jeep to the spare tire mount to power back up lights. So I need to figure out the max amps of the lights so I don't fry the wire and I'm not doing standard run-of-the-mill back up lights either. Not tapping in on the hot wire that feed the brake lights because I don't want to risk frying something that's on the OEM wiring circuit.
 

TeeKay6

Joined Apr 20, 2019
532
Anybody know where I can find a good chart that lists the of amps that that can run on a certain wire gauge? Optionally, also have an estimate of the resistance of the wire gauge to how long the wire is.

I've already tried googling it and not exactly the type of charts I'm looking for.

Scenario: What's the max amount of amps I can run on 16AWG that's approximately 15 feet long. I'm trying to run a hot wire from the engine bay of my jeep to the spare tire mount to power back up lights. So I need to figure out the max amps of the lights so I don't fry the wire and I'm not doing standard run-of-the-mill back up lights either. Not tapping in on the hot wire that feed the brake lights because I don't want to risk frying something that's on the OEM wiring circuit.
Search for "ampacity of copper wire"; you'll get plenty of info. Same for "resistance of copper wire".
 

oz93666

Joined Sep 7, 2010
701
16AWG is 1.5mm2 ... realistically, from my own practical experience 20A is fine ...even 30 A would not be disastrous , it would get hot and soften the plastic , but not catastrophic ...

Charts are always overly cautious and allow for the possibility the wire could be covered with something causing more heat build up ... 16AWG enameled copper wire can handle even more current than plastic insulated , perhaps 50A ..... This is of course when the wire is exposed to air on all sides to allow heat to escape ... when wound in a tight coil in a motor , the heat cannot escape easily so the current must be less

For cold whether ,0C , add 5 more Amps to above figures ....

Edit .... I just searched to see what I could find ...

" 22 A maximum for "chassis wiring..... Presumably more temperature rise is acceptable inside a chassis.....
If you have 16 AWG wire with a silicon insulation you'll find its rating to be substantially higher than cheaper plastic insulation"

https://electronics.stackexchange.com/questions/38515/what-is-the-max-current-for-awg16

The max current is determined by the temperature at which the insulation melts/breaks down ... silicon is better than plastic , "enameled" (varnished) wire is best and can tolerate a higher temperature and because the varnish is very thin is less thermally insulating keeping the wire cool , but it's easily scratched exposing copper .
 
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This https://www.powerstream.com/Wire_Size.htm is likely what you need. With calculators, you usually specify one-way run and the max desired voltage drop. A good number to use is probably <3%.

As always many things can come into play like insulation, ambient temperature, bundleing and fusing. The NEC doesnt want you to size a breaker for >80% for a continuous load, so a 10A breaker would be used for an 8 Amp "continuous" load. The NEC would define a stove in a restauraunt, continuous and in a home not continuous. I realize your talking about a car, but I wanted to illustrate the concepts.
 

oz93666

Joined Sep 7, 2010
701
This https://www.powerstream.com/Wire_Size.htm is likely what you need. With calculators, you usually specify one-way run and the max desired voltage drop. A good number to use is probably <3%.

As always many things can come into play like insulation, ambient temperature, bundleing and fusing. The NEC doesnt want you to size a breaker for >80% for a continuous load, so a 10A breaker would be used for an 8 Amp "continuous" load. The NEC would define a stove in a restauraunt, continuous and in a home not continuous. I realize your talking about a car, but I wanted to illustrate the concepts.
There is a big difference in the recommended current for domestic use (house wiring) ... they have to imagine the very worst possible scenario... that would be the wire in a loft or wall surrounded by 100mm of rock-wool insulation .. in these conditions the heat cannot escape and just builds up ... they give a max current of 3.7A in your link .
 

MisterBill2

Joined Jan 23, 2018
4,564
If you are putting it into a vehicle and one of your goals is reliability, then choosing the smallest possible size wire to save a few cents is a rather poor choice. For a load of up to 10 amps #16 wire fused for 15 amps can work, for up to 15 amps use #14, and for 20 amps use #12 wire fused at 25 amps. And if the jeep is actually going to be driven, then the toughness of the insulation matters quite a bit. Ten amps on #16 wire for the lights will be fine, use a 15 amp fuse to protect the connection if there is a short circuit to the frame. And the slight voltage drop in the wire will be less than the return circuit voltage drop in the body.

Certainly you can run a lot more current through the #16 wire, and maybe the cheap insulation will not rub against some edge that you did not notice, and maybe the fuse will fail before a fire starts, or the other wires get their insulation melted, but the fact is that it is no more work to install an adequately sized wire than one that will give serious problems after a while.
 

MisterBill2

Joined Jan 23, 2018
4,564
The TS is doing car wiring and it isn't/doesn't follow the same tables as house or industrial wiring as far as the ampacity. Resistance yes, amps no.

Be sure to read the paragraph above the chart - http://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/
Some areas in a vehicle are quite hot under normal operation, and wires in those areas do get quite hot even with no current flowing. And one thing not mentioned is the mecahnical durability requirement of the wire.
 

MaxHeadRoom

Joined Jul 18, 2013
19,457
Anybody know where I can find a good chart that lists the of amps that that can run on a certain wire gauge? Optionally, also have an estimate of the resistance of the wire gauge to how long the wire is.
I've already tried googling it and not exactly the type of charts I'm looking for.
You can also find charts that size according to application, ran in free air, plenum, harness etc.
Also you need automotive type insulation rating.
A local auto wrecker is a good cheap source of a scrap harness etc.
Max.
 
The wire gauge table for maximum allowed current does not know the voltage drop you accept at certain lengths because for 1000v a voltage drop of 10V is nothing but for your Jeep 10V of loss is too high.
You must simply calculate the voltage drop.
 

MrAl

Joined Jun 17, 2014
6,821
Hi,

It helps sometimes to think in simple terms.
Here is a simple chart that shows the voltage drops for various AWG size wires.
The current is 10 amps and the length 10 feet for each size shown.
If there is a return wire of the same size, double each voltage.
The power for each wire is given last.
If the temperature rises too much the voltage drop becomes higher.

#16, 0.40v, 4.0w
#14, 0.25v, 2.5w
#12, 0.16v, 1.6w
#10, 0.10v, 1.0w
#8 , 0.063v
 
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MisterBill2

Joined Jan 23, 2018
4,564
Hi,

It helps sometimes to think in simple terms.
Here is a simple chart that shows the voltage drops for various AWG size wires.
The current is 10 amps and the length 10 feet for each size shown.
If there is a return wire of the same size, double each voltage.
The power for each wire is given last.
If the temperature rises too much the voltage drop becomes higher.

#16, 0.40v, 4.0w
#14, 0.25v, 2.5w
#12, 0.16v, 1.6w
#10, 0.10v, 1.0w
#8 , 0.063v
I already provided the information about wires sizes 16, 14, and #12, with currents not wattages. And in each case the drop in the fuse will be greater than the drop in the wire at the max current I listed.
 

MaxHeadRoom

Joined Jul 18, 2013
19,457
You cannot take carte Blanche advice from a chart without knowing the application and situation the particular conductor is used in, every situation varies.
Max.
 
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MisterBill2

Joined Jan 23, 2018
4,564
You cannot take carte Blanche advise from a chart without knowing the application and situation the particular conductor is used in, every situation varies.
Max.
The TS mentioned that it was for backup lights on a jeep type of vehicle. I regard that as a fairly well defined application, and given the duty cycle of backup lights, that is a fairly specific situation.
IN ADDITION, the wire sizes, current ratings, and fuse sizing are applicable in a wide variety of instances. And my caution about protecting the insulation was especially appropriate.
Even so, I did not say that it was universally applicable in all instances for every occasion.
 

bwilliams60

Joined Nov 18, 2012
1,233
Here is a chart that I have used extensively in the automotive/truck industry and never had any issues. The wiring sizes may be a little larger than expected, but it works and leaves a comfortable margin for safety.
A couple of things about this post. The OP has mentioned that he is running backup lights on a Jeep and wants to tie into brake lights. Did I read this wrong? What he did not say was what year and model this Jeep was which makes me wonder about CAN bus and body controllers. You can't just tee into anything anymore because if it is body controlled, it is also current controlled. He did not say whether he was using LED or incandescent with his install as well which also plays into what size wiring and where are we wiring this? For this type of install, I would recommend a GPT or GXL insulated wire and 14-16 gauge should be sufficient for 15 feet.
If you can provide the year and model, perhaps we can give you more information on where and how to hook into your vehicle.
It is times like this that I miss the automotive section....
 

MisterBill2

Joined Jan 23, 2018
4,564
Here is a chart that I have used extensively in the automotive/truck industry and never had any issues. The wiring sizes may be a little larger than expected, but it works and leaves a comfortable margin for safety.
A couple of things about this post. The OP has mentioned that he is running backup lights on a Jeep and wants to tie into brake lights. Did I read this wrong? What he did not say was what year and model this Jeep was which makes me wonder about CAN bus and body controllers. You can't just tee into anything anymore because if it is body controlled, it is also current controlled. He did not say whether he was using LED or incandescent with his install as well which also plays into what size wiring and where are we wiring this? For this type of install, I would recommend a GPT or GXL insulated wire and 14-16 gauge should be sufficient for 15 feet.
If you can provide the year and model, perhaps we can give you more information on where and how to hook into your vehicle.
It is times like this that I miss the automotive section....
The statement was that the TS DID NOT want to tie in to the brake wire and possibly fry things. Mostly the fools have not gone to that poor choice of a digital buss to control all of the items. I actually ran into it when working with production line testers for GM vehicles. The grief produced by the buss, and the servicing problems that arose, were all a NASTY nightmare. The service part logistics challenges killed the project before it could do a lot of damage. Consider that each and every module will need a specific address, and every module will be unique to a specific position on a single model. The whole concept was STUPID and remains stupid.
 

bwilliams60

Joined Nov 18, 2012
1,233
My apologies, I did misread the part about the brake lights. Still need more info on the install.
As for modules and addresses, keep in mind that the industry is trying to drive independent shops out of business and keep shop repair times down. By placing everything on the BUS, everything can be monitored and diagnostics are kept to a minimum because it will all be self-diagnostic (haha) and technicians will be parts replacers. This is the goal right now and if you don't believe it, look at some VW models and the hierarchy of their wiring systems. We are not far off from self-diagnosing vehicles.
 
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