POE Wire Gague

Our team is putting a limelight on our robot and would like to power it using power over Ethernet as documented in the limelight manual. However, R60 says that even if we use a 5A breaker, we would still need 22 AWG wire, which is very difficult to find in Ethernet. It seems like they recommend the REV injector, which uses thicker wire to deal with this. This injector is too short for us, so we would need to wire our own using 24 AWG wire. Since we use 2 wires for each pair, would we be in compliance with R60? (I understand that we couldn’t insert them both into the WAGO, we would have to solder to another wire.)

I’m not sure, but could something like this solve your issue?

Don’t think that would be useful, it doesn’t seem to list a gauge but I would assume it’s 24 or smaller.

Sorry I wasn’t more clear. Maybe you could attach a short regular ethernet cable to the female end of the Rev POE cable and the robot radio, and then connect the cable I linked above to the male end of the POE cable and the ethernet of the Limelight.

You’re still passing the power through that cable, which seems to break R60

What wire of the REV injector is too short? Can you plug it right into the battery and then extend the power wires if needed?

We’re running the limelight on our elevator, so we would prefer to run a single Ethernet cable for both power and communication.

Ah! I missed that on R60. I guess you would need a 14 AWG wire then. We’re planning on mounting our limelight on a place that is similarly hard to run cables to, so please tell everyone what you end up doing.

Ended up asking on Q&A, seems to be illegal to power the limelight over POE without using a special Ethernet cable. (REV seems to be illegal but circumvents this by being recommended in the manual.)


Per R54, the radio must be powered from a [specific] 2A VRM port, so R60 allows wire down to 24AWG for this.

We wanted to power a limelight, which specifically says to plug it into the PDP, which has a minimum gauge of 22AWG on a 5A breaker.

Keep in mind I am not likely to be your robot inspector, but I would use this argument. Using a COTs POE injector, COTs Ethernet cable designed for POE. The Limelight manual recommends POE. COTs items are excluded from wire gauge requirements when used as intended. This is something Marshal would do.

1 Like

Trying to weaken your argument?

Still, the part of R60 following table 10-4 reads [emphasis mine]:

Wires that are recommended by the device manufacturer or originally attached to legal devices are considered part of the device and by default legal. Such wires are exempt from R60.

I would therefore have the limelight documentation where they recommend a POE cable handy for inspection if the question comes up.

The answer to the Q&A specifies “a team constructed wire”. This makes sense - you can’t “make” a 12 gauge wire using two 18 gauge wires to power a motor, and if you start allowing it in some situations but not others you run into issues around being able to consistently enforce it and around writing the rule properly for all situations.

Instead, try rephrasing your question. “Can a COTS POE injector, along with a COTS ethernet cable, be used to power a COTS computing device from a 5A breaker if the wires in the COTS parts are smaller than 22 gauge?” Ultimately, that’s what you would really prefer to do anyways, I think.

I would also include the section of the limelight documentation that details using POE.

  • (LIMELIGHT 1 ONLY) Ensure that your Limelight’s power jumper is set to the “E” position.
  • Connect a passive Passive PoE Injector to your PDP (NOT your VRM).
  • Add any breaker (5A, 10A, 20A, etc.) to the same slot on your PDP.
  • Run an ethernet cable from your Limelight to your passive POE injector.

It would require four, not just two, 18AWG wires to get the cross section of one 12AWG wire. This actually makes your point more strongly.

For my team we use a power over Ethernet adapter and cut off the plug for the power, strip the wires and plug them into the 12v 2amp port on the Voltage regulator module but we do this for our radio so it might need to go into a different port on the VRM

Good point… I wasn’t thinking about cross sectional area, I was thinking about the wire gauge rules surrounding breaker values - splitting 40A over two wires means 20A per wire, the rules say 18 gauge for a 20A circuit, it’s makes for simple, attractive math. Ignore the fact that one wire could carry more of the current than the other :slight_smile: It’s way to easy to screw up if you start running multiple strands to try to replace a larger strand!

I would like to add some caution to the above statements.

  1. In general, Ethernet cables are solid wire because they are installed in things that do not move. Since you are intending to use Ethernet, it can cause a failure of the wire with repeated bending. POE generally intends using 48 volts or higher as the injection voltage so that current on the cable is reduced. Know what current the limelite requires to be sure that #24 AWG can handle the current. Be prepared to show specifications. Personally, fudging the wire tables for #24 wire, I would be hesitant to run more than 1 amp on Ethernet cable and know that there is going to be a voltage drop on the wire.

Thanks for all the feedback!

You would be correct, that is basically what we want to do. I did initially think of that exception when checking if this was legal, though the specific recommendation of the REV injector worries me. I’ll probably end up submitting a second question as you recommended.

In the end, our team has decided to run a separate power cable to avoid the issue, and will likely take the same approach as with the radio of using PoE as backup if we can convince an inspector or Q&A to allow it.