Electrical n00b here. I am trying to create a circuit with 100 ultra bright white/yellow LEDs in parallel (controlled via a rPi)

I figured out that I need an external wall wart, rated at 5V, 5A.

The project require minimum sized wires, I was wondering would telephone wires be "thick" though to handle 5V with 5A?

If not, what would be the recommended gauge of wire to use for this project?

  • \$\begingroup\$ How long are the wires? Is there a series resistor for each LED? \$\endgroup\$ Jan 11, 2015 at 16:24
  • \$\begingroup\$ powerstream.com/Wire_Size.htm \$\endgroup\$
    – Majenko
    Jan 11, 2015 at 16:26
  • \$\begingroup\$ Yes there will be a resistor for each of your parallel LED. The wires combined will be less than 3 meters. \$\endgroup\$
    – Bill
    Jan 11, 2015 at 17:05

2 Answers 2


About AWG 20 (0.812mm) should be acceptable, use wire that is rated for 90°C or better. That's much heavier than typical telephone wires, and higher temperature rating than some. If you need the OD of the wires to be small or if you anticipate high ambient temperatures, you can use PTFE-insulated wire, which is often rated for 200°C.

I based that on a voltage drop of 0.5V (which will result in a change in brightness of about 25% with a white LED) and average (round trip) length of 3m, so resistance should be < 30m\$\Omega\$ per meter. It's also the NFPA ampacity recommendation for AWG 20.

  • 1
    \$\begingroup\$ +1 Off course your recommendation assumed copper wire and not aluminium or steel cable. \$\endgroup\$
    – GR Tech
    Jan 11, 2015 at 17:44

You would need to know the diameter of the wire and the length that is transmitting the high current. Knowing the wire diameter you can look up the resistance per foot (or per meter). The resistance value can be used to determine the voltage drop along the wire length. The voltage drop times the current will give you the wattage dissipated in the wire.

In the US some telephone wire is solid and some is wrapped with thin strands (in flexible cords). The flexible cord is likely not suitable for that high a current. The solid wire should be checked as above.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.