Wire Parameter Calculator September 20, 2007
This Javascript web calculator will calculate the resistance and ampacity for copper wire based on the gauge. Both metric (mm) and American Wire Gauge (AWG) are supported. Note: Ampacity is based on a curve fit to MIL-STD-975. To see the wire table that this calculator is based on as well as important information about wire insulation temperature ratings, click here.
Features:
- Results update as you type
- Several choices of units
- Units and other settings are saved between sessions
- Blog format allows user comments
Note: To go below 0 AWG, for example 00 AWG, enter -1 and so on.
Inputs:
| Wire Size |
Optional Inputs:
| Wire Temperature | Deg. | |
| Wire Length | ||
| Number of Wires in Bundle |
Results (per each wire):
| Resistance | Ohms | |
| Single Wire Ampacity | Amps | |
| Wire Bundle Ampacity (per wire) | Amps | |
| Copper Diameter | ||
| Copper Area | ||
| Copper Weight |
- Posted in : Calculators, Electrical Engineering
- Author : Brad
Comments»
Having an option to select aluminum wires instead of copper would also be handy.
Hi Gene,
That is a good idea. The spec this calculator is based on does not cover aluminum wires so I will have to think about how to scale and adapt it. For sure the resistance is easy to calculate, but the ampacity is the tricky one.
Brad
Who uses Aluminum wire these days? I thought they banned that stuff in the 70’s? Aluminum melts at a relatively low temperature and doesn’t conduct as well. I wouldn’t waste time calculating that.
Thanks for the Calculator BTW. It’s the best one I’ve used so far.
[Paul, Glad you like it! Thanks, Brad]
Can you determine the different speeds of a motor by checking the windings or wires of a 3 speed single phase motor using an ohm meter?
[Al, I don’t think so - or at least I don’t know how. Brad]
Paul, aluminum wire is not “banned” per se. Nor was its use discontinued due to the melting temperature, but the galvanic effect when bonded with other metals causing corrosion. It is still used in controlled environments.
All of those drop feeders to your homes and bussiness are “ALUMINUM” so Paul you are one of those who uses “ALUMINUM” wire these days!
Hmm,
If I put in a multistrand copper cable: 0.19 mm wire diameter, 252 strands, I get nonsense.
For a start, the calc is internally limited to 15 strands in a bundle, and the bundle amperage is lower than the single wire amperage at 0.777 Amp. Yet this is an 8 AWG power cable for ~60 Amp!
Also, I would like to see the voltage drop for the length in volts/Amp. This is important for 12 volt systems.
Hi Peter,
I should clarify that the “Number of wires in Bundle” is not for multi-stranded wire, but for multiple insulated wires (e.g. in a harness). When there is a bundle of multiple wires, each wire is derated to carry less current. Above 15 wires in a bundle, there is no additional derating. This is just the MIL-STD-975 way of doing things.
Calculating the voltage drop is a good idea. I will plan to add that feature.
Brad
Right, sorry. I have a totally different use in mind with my comments. And not being familiar with the MIL standard does not help!
Nevertheless, a calculator for multistrand wire would be very useful - to me.
Voltage drop in V/A is just resistance! Took me a bit to realise that!
Peter
Thanks for the calculator! It is a really handy and by far the best one I have found to-date. I hate to ask but is there any chance of a downloadable version that can run on windows as out here in the boonies there is no way to log on and use it when it is most needed…
Hi Gio,
I’m glad you like it. To use the calculator without an internet connection, save the web page to your hard drive. For example, with IE, make sure the menu bar is displayed, and then choose file - save - save as web page complete.
Brad
What about insulation temperature ratings? For example 200C Kapton wire can handle more current than 60C PVC. Some places say 12 AWG 200C wire can handle 55 Amps.
Hi Kelly,
You are right. Insulation temperature ratings are an important factor. They are addressed in the attachment linked in the main write-up above. I also updated the write-up to make this clearer. As for 55 Amps for a 12 AWG 200C wire, you are going to get different results depending on which spec you go by. The reason is the temperature the wire will reach due to self heating is greatly affected by the environment in which it is used and the specs are linked to the intended environment.
Brad
Hi Guys
Is it possible to make the standard in this calculator selectable so you can calculate against NEC or NFPA79 or (I’m Dutch) IEC60204?
PeterJan,
If you can get me a copy of the applicable part of those specs, I will look into it.
Brad
Please send me the information about Formulas for using circular wire in place of flat wire. I shall be so much thankful to you.
SHAFIQUE
SHAFIQUE,
We have the above calculator for round wire, and for flat wire please see:
http://circuitcalculator.com/wordpress/2006/01/24/trace-resistance-calculator/
If these do not calculate what you need, please let me know.
Brad
I have a rectangular conductor that I would like to know the ampacity of. It is not a PCB trace, it is a turn in an electric machine.
I have the following information for an operating point (all values are per turn).
1. Operating current 245A,rms (line to neutral)
2. Operating temperature 165 C
3. Copper losses per turn 36.79W
4. Cross sectional area 4.3mm width (X) 2.84mm height =12.212mm^2
What I dont know
5. Length of the turn (I have an idea what is fesible, but I dont know exactly)
Lets call it right now a single conductor, in reality there are 4 turns per slot of this conductor. However that answers your “wires per bundle question” which I believe is more properly termed strands per turn at least in machine design lingo.
I know that the machine can do this, what I am curious about is how much current I can pump before this coil melts essentially. I know that its actually more complicated than that and that the stacking of coils, skin effect and induced fields will actually make the heating different, but it would give me a good start just where the copper itself melts.
Hi Randy,
That is a good question and indeed it is not a simple question. Even if we knew the power loss in the wire, we do not know the thermal resistance from the wire to the ambient temperature and I suspect this thermal resistance is very different in a machine than in a cable bundle since the heat path is very different. Of course copper/insulation melt/burn at specific temperatures not specific currents. Finding the ampacity amounts to solving a thermal problem where the heat source is the joule heating of the wire. I am afraid the general ampacity curves for wire would not be applicable to your machine problem, and I unfortunately don’t have curves or equations for machines. I think you would have to do a detailed finite element thermal analysis or determine the thermal impedances experimentally.
Brad
I have a generator of 250KVA and 230V 3-Phase. The length of wire is 50 meters. Of what cross-section and of how many strands cable should use?
S. P. Bhardwaj,
You will first need to calculate the current. Then, based on the allowable voltage drop and ohms law, choose a wire that has low enough resistance to work. In addition, the wire you choose will have to be rated to handle the current and meet all applicable local codes. The number of strands inside the cable varies by design and just the rated current is important. I added the following calculator to my site [1]. You may also find [2] helpful.
Brad
[1] http://circuitcalculator.com/wordpress/2008/01/05/3-phase-calculations/
[2] http://baen.tamu.edu/users/stark/AGSM325_files/Lecture/4%20WiringVoltDrop%20Handout.325.pdf
Could you please settle a question we have? Please define ‘Wire Bundle Ampacity’. Is the number shown, amps per wire in the bundle, or is it the total amps in the bundle?
Thanks,
larry
Hi Brad,
Does your calculator apply to single wires coiled around a generator core? I’m trying to calculate the number of turns required and wire diameter required for some driver coils to saturate the cores with 12VDC @ 2A.
Thanks,
Denny
Denny,
See comment 20 above. I don’t think this calculator would apply for your situation either.
Brad
Hi Larry,
Good question. Wire Bundle Ampacity is per wire. I added a note to the calculator where results the results are displayed.
Brad
Hi friends,
Does any one know of a free software that could help me to do load calculations of motors, required power cables, selection of breakers, short circuit calculations etc. for a medium type project? At least to save the time I thought using software is better rather than manual computing. I have gone through browsing, found all those are very expensive.
Hey Brad, thank you so much for this calculator. I use it probably once/week on average!
One thing I’m looking for right now and missing is the ability to calculate the mass of copper given the inputs. It should be difficult since you’ve got diameter and length. I could look up density (which is what I will do). Of course, it would just be an estimate (issues such as insulation mass and stranded vs. un-stranded) but would be useful.
Thanks again!
Hi Rob,
Adding the mass calculation is a good idea. I’ll put it on my “to do” list. For reference, the density I found for copper is 8.96 g/cm^3.
[Update 2/29/08: I added the mass calculation to the calculator. Brad]
Hi Brad,
Is there a formula which can you give for non-insulated wires?
Thanks,
Inanc
Hi Inanc,
Sorry, I don’t have such a formula.
Brad
Dear Brad,
Can you calculate current carrying capacity of flexible fluoro-rubber insulated wire of 200sq.mm. copper conductor having temperature rating of 200deg.C.
Ashish,
Specialty wires with significantly unique form factor or thermal properties may have different current carrying capacity. I would ask the vendor for guidelines or do thermal analysis.
Brad,
Nice calculator.
I am trying to figure out how to calculate conductivity loss on CU wires. I know your program does this automatically, but I would like to be able to do the calculations my self. I found a formula in wikipedia but how do I know what are the constants for the material used, copper in this case?
Hi Celso,
Most material constants are also on wikipedia (by material name) or you can Google them.
Best regard for the calculator
being able to go below “0″ would be nice.
Hi Ken,
You can go below 0 AWG. For example, for 00 AWG, enter -1 and so on. Is that what you meant? I added a note of this to the calculator. Thanks!
hi brad,
How to calculate twisting of flexible copper conductor just like 0.5 sq.mm to 50 sq.mm and how to fix the lay length.
This calculator is very good for small Jobs to wiring.
K.Senthilkumar,
Sorry, but I did not quite understand what you are trying to calculate. I don’t know if this will answer your question, but check out the link below. Maybe it can help…
http://www.fiskalloy.com/Percon/laydir.html
Thanks for your co-ordination . I have check the above said website that which i want to ask with you i have calculated which i want from your formula and your answer almost suitable for the lay length which will be diffferent lay length for different sizes.It means we can’t do fix lay length.Thanks
Just found out about this calculator, great tool. I was reading past posts and the one about “who uses aluminum now?” well, I just finished a job in Chile and had to relocate some electronics several kilometers and the mine manager asked if they could use aluminum instead of copper wire. I asked why and he responded….”Nobody steals aluminum wire!” Who would have thought?
Hi,Brad
What is different between house wire/Building wire and cable ?
K.SenthilKumar,
This is just a guess, but I think those terms (house vs. building wire) would indicate that the wire/cable meets certain regulatory requirements. Depending on the region, the safety codes could be different for commercial buildings vs. houses. Other types of wire may be designed to meet regulations for automobiles or aircraft. This brings up an important point - that there are electrical requirements as well as regulatory requirements in selecting wire.
thanks a lot. i am looking for this type of calculation since long time a go. it is very nice gift for me .
thanks
The calculator is very usable for us. However the derating formula of the MIL-STD-975 give a litle higher current than the calculator. Our example is a bundle of two cable #16. Any how the result of the calculator is conservative and very usefull. Congratulations
Daniel
Hello Brad,
I am testing defibrillator pads and have noticed that manufacturers are using 15 strand 18 AWG PVC coated wire.
The energy from most old defibrillators is 360 joules. I wish to hook up a 50 ohm resistor in series from with one of the pads.
I know that the pulse / discharge lasts 5 ms and measures approximately 4.4KV. Is there a factor for your calculator that I can use to get the ampacity for short bursts? I am figuring over 80 Amps for the 5 ms.
Hi J. Moore,
I recommend you look at it in terms of the RMS current of the short bursts. You may use the RMS calculator here: http://circuitcalculator.com/rms.php
You can also use the formula for the RMS of a pulse to work out the allowable duty cycle and time between pulses. For example, assuming a rectangular pulse from 0 to I_peak,
I_rms = I_peak * SQRT(Duty_Cycle)
Duty_Cycle = (I_rms / I_peak)^2
For 18 AWG wire, the I_rms should be limited to 8.56 Amps, so for an 88 Amp pulse, the duty cycle should be limited to (8.56/88)^2 = 0.00946
Duty_Cycle = T_on / T_period
In your case, T_on is 5 ms, so the allowed period between pulses would be
T_period = T_on / Duty_Cycle = (5 ms) / 0. 00946= 528 ms
I change temp! but current not change (current change follow temp) help me please….
Hi Simon,
Presently, the temperature input is only used for the resistance calculation. For the wire derating with temperature, please see [1]. It is a good idea for me to upgrade the calculator to include the temperature derating automatically. I will put that on the “to do” list. Thanks!
[1] http://circuitcalculator.com/wordpress/wp-content/uploads/2007/12/mil_std_975_wire.htm