OK - in theory I have a BSEE degree from 1974 but in reality it was a Computer Science degree so I need help to make sure I wire (mostly in wall) this correctly and do not burn down my new house.

And a BIG THANK YOU in advance for reading this - I have tried to include everything in an orderly fashion but please let me know if I am unclear anywhere.

Please see the attached diagram

enter image description here

  • Q1 - Wire Guage Computation for the Orange Power wires - Each Side: 18 Amps, 90 Watts 16 ft (one way); Total: 36 Amps, 180 Watts 32 ft (one way).

    • Q1a - Do I compute wire size based on each side: 18 Amps, 90 Watts 16 ft (one way)

    • Q1b - Do I compute wire size based on each side: 36 Amps, 180 Watts 16 ft (one way)

  • Q2 - Wire Gage Requirement - According to this web site:

    • Q1a requires 14ga at 1.0 drop multiplier or 12ga at 1.5 multiplier
    • Q1b requires 8ga at 1.0 drop multiplier and 8ga at 1.5 multiplier
  • Q3 Assuming I have not made a glaring mistake above it appears that it would be cheaper and easier for me to use two DC5V 20A 100W LED supplies instead of one DC5V 40A 200W LED as in the second diagram

enter image description here

Now I would not need anything larger than 16ga wiring?

  • Q3a Does the above make sense?

  • Q3b Given that I actually have four "sides" (rather than the two shown) I will need 4 power supplies (NOTE: I plan to be able to turn each pair of "sides" on and off by each of two wall switches which will control power to the supplies). Is the brand/type of supply I am using overkill for this application?

    • Q4 I have assumed that within reason the length of the control circuit is not an issue - correct?

    • Q5 I would prefer to control all of this from one Arduino so I have shown the control wiring as a daisy chain including each "side" and the small 12 LED strip shown at the bottom of the diagrams. I also would daisy chain in the second pair of sides mentioned just above. Given that the strips I am using have a dual pair of leads for the VCC and GND and that I am using different 6 power supplies total how do I wire this (I assume I can get polarity correct to prevent shorts). Or am I simpling forgetting my EE training and I do not have to worry about parallel connections between DC connections?

    • Q6 I just realized I may have a problem if I turn off power to one Power supply will that set of leds try to power off of the control line?

    • Q7 Am I making this too complicated - do I really need a separate Arduino for each power supply?

  • 1
    "Please see the attached diagram.", where is it? - Also all your links point to the same url. – Harry Svensson Jan 20 '18 at 21:40
  • Q3: what voltage to the LED strips require, series powering indiviually addressable led modules seems impractical. – Jasen Jan 20 '18 at 21:42
  • I was going to say this belongs in electronics.SE but it looks like they migrated it from there. Doesn't fit here either..... – Tyson Jan 20 '18 at 23:46
  • What application do you have which requires these LEDs be individually addressible? That realy does make things much harder. – Harper - Reinstate Monica Jan 21 '18 at 0:45
  • This is for some fancy shelf lighting for my wife's artwork - she likes to tinker with the color and have light only on parts of the shelf – dpressm Jan 21 '18 at 1:33

OK, that site has really misled you in terms of wire sizes. Wires have capacity based on amperes not watts. That means a 14AWG cable can carry 3600W in a 240V circuit, but only 75W in a 5V circuit. Both are 15A, which is the statutory maximum for 14AWG wire. Similarly 12AWG maxes at 20A, and 10AWG maxes at 10A. 8AWG is 40A.

However, your limiting factor will actually be voltage drop. Because there are microcontrollers in the strip, you need to - if I recall my TTL spec, it's +/- 5%, so 4.75-5.25V. That means you can only have 0.25V voltage drop combining all the voltage drops together, including the voltage drop along the strip itself. Your drawings show feeding the strip in a lot of places. That's the right idea. With these cheap strips, assuming 0.10V drop down a 1m length of strip is hopeful, so you can tolerate 0.15V of additional drop in the distribution wires. And that's where you'll get nailed.

You need to carry 18A from the power supply to the first strip, 16 feet (except it's round-trip, so 32.) Let's run the math a bit.

Try 12AWG wire. 0.0016 ohms per foot. x 32 = 0.051 ohms = R. I is 18. E=IR E (voltage drop) = 18A * 0.051 ohm = 0.92 V. Good grief! That won't do!

OK, well suppose we do a 12AWG homerun from each strip to the supply. I is 3.6. E=IR 3.6A * 0.051 ohm = 0.184 V drop. gahhh, close enough. You can bump it to 10AWG if you really want to.

How about busing with fatter wire? Rather than iterate, let's work backwards, E is our max tolerable (0.15V), I is 18A. R becomes 0.00833 ohms. The most resistance we can accept is 0.00026 ohms per foot. You don't want to know what wire size that is, but its last name is "KCMil".

... and you thought you were going to use 16AWG... SMH the things you read on the Internet... and this is why I said the 5V makes it much harder. If this was 12V, you would not have learned the term "KCMil" today.


  • Q1: Neither one. Trying to run 18A or 36A down a single bus is doomed to failure, since power loss due to voltage drop is a second order of amperage. The only thing that is not insane is a separate 12AWG homerun from each 1m strip back to the power supply.

  • Q2: 10 or 12 AWG depending on how voltage-drop-tolerant you are. LOL 16 AWG LOL... I wish you had tried it, I would love to hear how it turned out.

  • Q3: In case you haven't figured this out by now, use the number of power supplies that lets you move the power supply as close as possible to the point of use.

  • Q3B: You are linking cheap Cheese power supplies, and it's a big mistake to try to run those anywhere near their nameplate rating. They're just not that well built. If you were using GE supplies, different deal.

  • Q4: The control circuit looks reasonable though I might try branching that instead of a big long end-to-end. Don't make it a loop.

  • Q5: I would not parallel the power supplies. That shouldn't be a problem if you do a separate homerun for each 1m strip.

  • Q6: If you don't parallel the power supplies, that should make backfeeding impossible, but in any case, don't allow it.

  • Q7: unless there's a signal propagation problem, I would want one central control unit, so one Arduino. You might try having the Arduino on its own supply, or at least power it with a separate homerun.

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  • 16 gauge would have held on that load but since it is outside of a controll enclosure 16 awg is limited to 10 amps. NEC 725.43 if it were inside a control enclosure 16 awg is limited to 40 amps NEC 430.72. , there is 1 typo I know you meant 10 awg maxes out at 30 amps. The 3% voltage drop is a guideline and if the strips would work it would not be a code violation to have 3%,5% or even more. I also agree with not paralleling switching power supplies they may not play well together. Analog or transformer based supplys don't have the same problem as switching supplies in parallel. – Ed Beal Feb 21 '18 at 23:13
  1. I would advise you to power the leds with higher voltage (by managing series matching said higher voltage). 5V is ok for control, not for power over long distances. Look for 12V or 24V or even 36V. You will save on wires (yes wires have to be thick) and MAYBE you can use only one 200W supply. With 24V it's already much easier.

  2. How are you interfacing the arduino with the LEDs? For DC it can be done easily with power MOSFETs or with relays if you want to manage the AC directly.

Please post schematics, wiring diagrams and more datas of all the components. So far, we have only a link to the power supply vendor... :(


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I would change the plan a little. I would place the power supplies close to the location of the led strips I would get a box to put the Adriano in with 6 relays (they make them in 1,2&4 combinations) use the arduino to switch the hot leg for each. Now you are using 120v for the long run to the power supplies and there will be no voltage drop to worry about or ampacity issues to the led strips. I did something like this with one of my grandsons last year. we had 12 channels ( 3 sets of 4 relays) he programmed the channels in different patterns and we put a pot in so he could adjust the speed, this year we are going to add Wi-Fi. Everything is in a electrical box and there are 6 duplex outlets with the tab broke so 12 channels. I did use a 9v dc adapter to power the system . we had to stop at 12 channels because I wanted the entire system to run on a 120v 15 amp circuit and 12 was our max for the light strings if he turned them all on at the same time. By switching the 120v supply to the power supply by using this method on a 15 amp 120v circuit you could power close to 250 amps at 5 volts and use 14 awg wire to the power supplies. Now comes the part where we go to the mfg's listing instructions for the connection to the LED strips and this is usually 16 gauge or smaller. The mfg instructions on up listed devices trumps the NEC in fact the NEC requires that the mfg instructions be followed. Remember that inside a controll enclosure 16 gauge is good for 40 amps, I have seen some led strips using 20 gauge wire for over 10 amps I can't remember if it was 5 or 12vdc but this would be legal if it was how the listing instructions said to connect. Just something to think about.

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