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I want to use a CAT6 (24AWG) RJ45 cable to carry a total of 2A at 48V. As per the AWG Chart, I see that the Maximum amps for power transmission is 0.577A but the Maximum amps for chassis wiring is 3.5A. I am not going to be using this cable in a bundle and it will be in lengths up to 10ft.

Am I OK here? WHich number do I follow: Maximum amps for chassis wiring or Maximum amps for power transmission?

If this is a bad idea, are there other DC cables I can use for a 10ft range carrying 48V and 2A?

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Neil Dey
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  • 2A feels fine. Resistance is 0.5 for one pair, so 0.125 for the whole cable. Peanuts. –  Mar 28 '18 at 17:14
  • Be careful not to connect a normal ethernet to your connector. You will burn it badly –  Mar 28 '18 at 17:16
  • Yes, that is why I am planning to use the PoE standard so as not to damage standard ethernet devices. Thanks for the input. – Neil Dey Mar 28 '18 at 17:23
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    If you are using PoE as per 802.3, why are you worrying about the current through your wires? The spec has been made so that you can't exceed the ratings, whatever you do (provided that all the equipments are conformant). – dim Mar 28 '18 at 18:32
  • So you plan to send 96W using PoE (15.4W maximum, 13W delivered and maximum 350mA/pair). PoE+ is (30W, 25.5W and 600mA/pair). [Siemens](http://www.siemon.com/uk/white_papers/08-06-09-poe-and-operating-efficiency.asp) – StainlessSteelRat Mar 28 '18 at 19:36
  • max amps for power is as conservative as one can get; bundled cables with full insulation and no allowable temp increases, like undersea cables. you can 10X that under typical conditions. – dandavis Mar 29 '18 at 00:11

2 Answers2

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The Table you show is generic, not taking into account wire length or insulation material.

The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle.

The maximum current you can put through a 24AWG conductor depends on the insulation material of the cable.

A lot of CAT cables use HDPE Insulation to insulate conductors. Jackets vary from PVC to LSZH to protect cables.

Cat6

Ignoring the jackets.

HDPE is high-density polyethylene. From Current Carrying Capacity of Copper Conductors, has a maximum temperature of 90°C. At an ambient temperature of 30°C, 24AWG has a maximum current of 7A.

So 2A for a 10ft cable will not be a problem for 24AWG wire.

StainlessSteelRat
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Too Little Information! If this is ONLY for your personal use and not intended to be given to or sold to another party, you can do whatever will work for your needs. Is your "Load" going to be designed as a PoE compliant device, using only (2) of the (4) 24AWG conductor pairs for powering the load? If this is simply a power supply cable (no data or information imposed on any of the cable pairs), then each pair of which there are 4 can be paralleled to give you a DC resistance equivalent of a 5 ft length of #24 awg which is 0.128 ohms (total conductor resistance). At 2 amp load flowing through the 0.128 ohm 10 ft conductor, you have a total heat loss of 0.512 watts of heat generated and that equals 0.0512 watts per foot which amounts to 0.0512/8 watts per 24AWG conductor per foot. Definitely not a deleterious rate of heat to dissipate! A 0.512 watt transmission loss when powering a 96W load is a little over a 1/2% overall power loss, which is efficient and acceptable. IF you are designing a product to eventually be marketed, that is a totally different set of design standards and Code requirements that are much too complicated to enumerate on this platform.

John Suttles
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    This is not a personal project. I am going to follow the PoE pinout but my device is not an ethernet device. I am only planning to follow the PoE pinout in case someone accidentally plugs in an ethernet device, i don't want to damage it. – Neil Dey Mar 28 '18 at 21:18
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    Using a common cable as a power cable is just asking for problems. You'll put some labels but someone will insert something and make it go boom. Common sense is not that common. Nature always invents a bigger idiot. And some of them are pretty smart. User in your other thread gave you the best answer in the comments. Off to the hardware store and pick up some wire. – StainlessSteelRat Mar 28 '18 at 22:48