AC DC Cable Sizing

It turns out that a lot of information online is incorrect about how to size power cables or speaker cables.

After a lot of technical research and obtaining the correct formulations we can now identify websites that offer accurate information.

First some notes:

What is a power cables acceptable voltage drop value?
3% is considered a good standard for acceptable loss. Under 3% is the gold standard.
4% is a bit worse but in a pinch this would be acceptable if the equipment non-sensitive like a pump or fan.
5% this would be the worst case and once again only for non-sensitive equipment.
10% there are websites that literally think this is an acceptable loss but it certainly isn’t and with high loads this can be dangerous.

Can I use CCA/aluminium cable instead of pure copper?
Firstly always AVOID any CCA/aluminium (silver looking) cable at all costs. If it cheap and is silver coloured then its likely to be CCA.
CCA is bad for many reasons, first is that it has a higher resistance that increases when it gets hotter. This reduces its power throughput and effectively increases fire risk and equipment failure or at least reduction of performance.
There are cables that are pure copper with an actual silver coating for anti-corrosion but they will be marked as pure copper.
If you have absolutely no option but to run CCA remember you will need to increase the size of the cable to work safely.
All calculators give a Copper size rating to convert to CCA add 56% onto the original size. Example: 4mm2 Copper = 6.24mm2 CCA.
Power cable, speaker cables and network cables should all be PURE COPPER! Network cables that are CCA only work as fly leads for non-PoE applications.
All long distance network cables that require high quality and/or PoE based should only ever be pure copper cables ideally 23AWG (optimal) or 24AWG but not 25+AWG. Also in the year 2025 try to use CAT6 for Gigabit or optimally CAT6A for 10 Gigabit future proofing.

How much power/current/wattage can you put through 100m of CAT5e pure copper network cable?
Its fairly common to have a PoE++ switch to output 100W through a network cable of up to 100m but its also possible to do more at a higher voltage.
28AWG/0.081mm2 = 65.3 ohms/1000ft = Never use for PoE
26AWG/0.13mm2 = 41 ohms/1000ft = Never use for PoE
25AWG/0.16mm2 = 32.4 ohms/1000ft = Only use for very short runs of PoE
24AWG/0.21mm2 = 25.7 ohms/1000ft = Acceptable for PoE
23AWG/0.26mm2 = 20.3 ohms/1000ft = Optimal for Type 1 to 4 PoE – Best option
22AWG/0.33mm2 = 16.2 ohms/1000ft = CAT8 Optimal for extreme PoE

Never use the flat cables for PoE as they are usually unreliable and often use very low grade cores and have fake speed ratings.
A typical CAT5e network cable is rated up to 300V at 0.5amps/500mA at 60-70’C operating temperature @ 75’C max cable temperature.
At 100ohms/km DC resistance and 100ohms impedance with dielectric strength of 1.5kV for 1 min or 2.5kV for 2s is fairly common.
Note: PSE is the power coming from the switch or source power supply and PD is the power received at the end of the cable for the device.
PoE (802.3af – Type1) 44-57v(PSE) , 37-57v(PD), 400mA = 15.4watts (PSE) @ 12.95watts(PD) @ 350mA per pair (700mA total @ 2x)
PoE+ (802.3at – Type2) 50-57v(PSE) , 42.5-57v(PD), 600mA = 30watts (PSE) @ 25.5watts(PD) @ 600mA per pair (1200mA total @ 2x)
PoE++ (802.3bt – Type3) 50-57v(PSE) , 42.5-57v(PD), 960mA = 60watts (PSE) @ 51watts(PD) @ 600mA per pair (1200mA total @ 4x)
PoE++ (802.3bt – Type4) 52-57v(PSE), 41.1-57v(PD), 1400mA = 90/100watts (PSE) @ 71watts (PD) @ 960mA per pair (1920mA total @ 4x)
Older PoE Type1 if you start with 48v @ 13.63watts over 100m you will have 45.62v @ 12.95watts at the end of the cable with around 5% current loss.

Examples: PoE to PoE++
Cat5e 23awg PoE Type1 at 48v 13.63watts PSE over 100m @ 0.28amps delivers PD of 45.62v @ 12.95watts giving a loss of 10.8watts and 2.38v.
Cat6 23awg PoE++ Type4 at 51v 78.99watts PSE over 100m @ 1.55amps delivers PD of 45.84v @ 71watts giving a loss of 7.99watts and 5.16v.
Cat6a 23awg PoE++ Type4 at 51v 78.99watts PSE over 100m @ 1.55amps delivers PD of 45.84v @ 71watts giving a loss of 7.99watts and 5.16v.
Cat7 23awg PoE++ Type4 at 51v 78.99watts PSE over 100m @ 1.55amps delivers PD of 45.84v @ 71watts giving a loss of 7.99watts and 5.16v.
Cat5e 24awg PoE++ Type4 at 51v 81.86watts PSE over 100m @ 1.61amps delivers PD of 44.23v @ 71watts giving a loss of 10.86watts and 6.77v.
Cat5e 25awg PoE++ Type4 at 51v 86.17watts PSE over 100m @ 1.69amps delivers PD of 42.02v @ 71watts giving a loss of 15.17watts and 8.98v.

Cat5e 23awg PoE++ Type4 at 51v 81.8watts PSE over 100m @ 1.6amps delivers PD of 44.27v @ 71watts giving a loss of 10.8watts and 6.73v.
Cat5e 23awg PoE++ Type4 at 51v 75.61watts PSE over 50m @ 1.48amps delivers PD of 47.89v @ 71watts giving a loss of 4.61watts and 3.11v.
Cat5e 23awg PoE++ Type4 at 51v 71.83watts PSE over 10m @ 1.41amps delivers PD of 50.41v @ 71watts giving a loss of 0.8watts and under 0.59v.
What if you need to run 230v over CAT5e 23awg? Well its actually possible as the cable is 300v and 0.5amp rated but use a RCBO ideally 1amp or less for circuit protection.

Examples for 230v AC/DC:
Cat5e 24awg 230v @ 103.41watts in 1x Bonded Pair over 100m @ 0.45amps delivers 222.42v @ 100watts giving a loss of 3.41watts / 7.58v (4%loss)
Cat5e 24awg 230v @ 206.82watts in 2x Bonded Pair over 100m @ 0.9amps delivers 222.45v @ 200watts giving a loss of 6.82watts / 7.58v (4%loss)
Cat5e 23awg 230v @ 102.65watts in 1x Bonded Pair over 100m @ 0.45amps delivers 224.06v @ 100watts giving a loss of 2.65watts / 5.94v (4%loss

When using bonded pairs for extra power, use twisted pairs like blue and blue/white together. Don’t use non twisted pair like orange and brown.
In standard PoE applications blue(P4) and blue/white(P5) is DC+ Positive and brown(P8) and brown/white(P7) is DC- negative for TYPE T568B color coding only.
See PoE calculator below.

I saw another website where it says to use a thinner cable?
And this is the problem. Some websites literally suggest cable sizes but they have no understanding of anything.
They typically look at the load value of a cable which is effectively the carrying capacity under 1 meter and then assume that is true for any length.
Distance really does matter. The higher the watts/amps of a cable the more critical it is. 100a at 50cm vs 2m is massively different cable sizes.

Cable temperature rating what does it mean?
Cables are rated for values like 60’C or 75’C or even 90’C and you really need to be aware of this value.
When your cable is in operation it will warm up. The closer the cable is to its load capacity at X length – the hotter it will get.
If your cable goes over this value then it will melt and/or cause a fire because it will effectively act like a heating element.
The higher the temperature rating the better but don’t go an run that cable at its limit as the risk is high too.

How to calculate fuse sizes correctly?
This is actually quite complex but here are the basics.
Typically a fuse needs to be a bit bigger than the max load of the devices approved current rating but not bigger than your cables rating as per the chart below.
For most instances take the device requirements and simply add 25% – so a 100a load will require a 125a fuse.
If your device is a pump, motor, inverter or other item that has sudden power draws then you can add 75% with a dual element fuse but make sure your cable size is correct.
There are different types of fuses even at the same rated amperage but you will need to look into this if you have specific issues.
Don’t exceed the cables rated carrying capacity as per the fuse sizing chart or calculator below.
Don’t use a AC fuse for a DC circuit and visa versa. Switches are also AC DC specific.