Re: 24 guage wire

[Lewis Gardner <lgardner@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

Robert L Bass wrote:

> If we use four 24-gauge wires we can carry 4 x 0.577 amps.
> That is just a tad over 2.3 Amps total,

Not safely.

This sort of brute force math can get you into trouble. There are so
many variables involved in this sort of calculation that the only real
answer is that the ampacity of "four 24-gauge wires" is LESS than 2.3 amps.

As I stated in another fork of this thread my guess is that the OP was
referring to something like a cat5 cable since it is the most common 24
AWG cable used in HA applications. The twisted pairs in a cat5 cable and
the insulation used are not designed for current carrying applications.
The issue is that closely twisted pairs in a PVC jacket are not able to
shed heat easily. Cat5 is communications cable not a power cable. The
construction of power cables is quite different.

To give you an idea of some derating factors refer to:

www.okonite.com/engineering/ampacity-correction-factors.html

The closest correction factor to this case is at the bottom of the page
titled "Group Correction Factors", "NUMBER OF CABLES IN AIR". The table
gives a derating factor of .84 for 4 conductors horizontally. So the 2.3
amps turns into 1.9 amps. I think this is optimistic since the
conductors are not in air but instead are bundled in a jacket and
additional derating would likely apply

The only good reason I can see joining conductors in a cat5 cable is to
reduce voltage drop.

A good example of this (using the dandy calculator in Dave Houston's
post) is a 12 VDC 250 mA cordless phone located 100 feet from the wiring
closet. If you had a spare cat5 and used two sets of 4 conductors to
power the phone remotely the voltage at the phone would be 11.7 volts
(2.7% drop). Compare that to 10.7 volts (10.9% drop) with two single
conductors.

On 18 AWG wire, 12 VDC at 2.3 Amps the longest distance you can go with
a 5% voltage drop is 20 feet. At low voltages ampacity is NOT the issue,
voltage drop is.

If you want to run several amps from one place to another use a properly
sized power cable. In HA work (low voltage) the sizing calculations will
tend be voltage drop not ampacity.