# Split current load through different wire

I have to power an electronic board with this flat wire band. But the problem is, the maximum current load is way more than a simple wire can held (1.7A). Each wire of the band is 28AWG with a current rating of 0.7A according to this file.

How many wire for VCC and GND do I need? $\frac{1.7}{0.7} + 1 = 3$ wires? Or is there more calculations to do?

• What connector are you gonna use and what is its current rating? What are you going to power with it? You have to consider cable length, voltage drop, temperature rise, etc. That seems the wrong cable to run almost 2A through unless you can use many parallel strands. – Wesley Lee May 16 '17 at 15:17
• also take into account that not every wire is created the same, it's very possible that significantly more current will go through a single wire than through the others. – ratchet freak May 16 '17 at 15:18
• @WesleyLee I plan to use many strands but I don't know much (this is what the topic is about). But, as said ratchetfreak, current can go through a single wire instead of splitting the load through all available strands. – M.Ferru May 16 '17 at 15:23
• You didn't answer any of my questions.. There are many other considerations to make, none of which are possible without more info. – Wesley Lee May 16 '17 at 15:25
• @WesleyLee I'll use pinhead with this connector, I want to power LED. Cable length is pretty short, 3cm – M.Ferru May 16 '17 at 15:29

Actually current will tend to self balance across wires. The one taking the bulk will heat up and gain resistance so the others will become more desirable.

However, length is critical, and voltage drop along 28AWG will be high for any significant distance.

In this equation you also need to back off your math by at least a factor of two. YOU DO NOT want to run at the rated limit for 28AWG or it will overheat.

Not sure why you need to use ribbon cable for this application, but there are alternative solutions available that will connect to a standard .100 ribbon cable header that allow you to use heavier and more suitable wire types using crimped pins.

• I'll maybe go through a higher current rating ribbon cable like this one. AWG26 got 1.7A current rating, if I use 2 strands it will be fine. – M.Ferru May 16 '17 at 15:37
• @M.Ferru you still need to de-rate though. Ribbon cable has entirely different thermal characteristics to single wires. – Trevor_G May 16 '17 at 15:43
• Okay, I'll follow your advice, change the type of wire. Single wire seems to fit more my need – M.Ferru May 16 '17 at 15:44
• The tempco of copper is not very high, so self-balancing is not something to count on. Not even a little bit. – WhatRoughBeast May 16 '17 at 18:44
• @WhatRoughBeast agreed, hence my prod to de-rate and go another way. – Trevor_G May 16 '17 at 18:46