Ilan:
200W @ 60V implies a current draw of 3.33A. The PoE scheme uses a balanced
feed that effectively parallels two 24 AWG wires per direction and requires
two pairs for a complete DC circuit. Paralleling effectively lowers the gauge
by 3 i.e. 2ea 24Ga is comparable to 1ea 21 Ga. Also note that to get lower
signal loss, some CAT5 manufacturers use 23 AWG conductors, but this depends
on what you buy. Lowest cost won't use that trick. In any instance, to a
first approximation one 24 Ga pair can handle 2 X .577 = 1.15A, which implies
that PoH requires four pairs for 3.3A; two in parallel each for power and
return, equivalent to 18 AWG. Standard ampacity tables will show that 16
gauge is required for power transmission up to 3.9A, but that assumes a single
round conductor. Here, the distribution of current over multiple conductors
should enhance thermal dissipation, but ultimately the criterion is how much
power is lost per unit length of cable. 200W in at maximum distance can mean
rather less at the far end. Most users would be disconcerted to encounter
ethernet cables that are warm to the touch. And no power limits? At these
currents I would worry about hot plugging eroding the contact plating in the
long suffering RJ45 connectors.
Also note that the Mil Spec for Southern Dialect defines the spelling of the
second person denominative as y'all. The plural is 'all y'all'.
Orin Laney
On Wed, 26 May 2010 14:50:21 +0300 Ilan Cohen <[email protected]> writes:
Hi ya all
There is an exciting new technology emerging called PoH (power over HD
Base
T) intended to deliver 200W (DC- up to 60V) using Cat5, Cat6 cables.
One of the main applications will be powering TV screens. Now the
screens can
be very flat and powered by only one Cat5 cable which caries power data to the
screen.
A big challenge here is that we are not in power limited circuit
anymore, as
it is with PoE circuits.
Your opinion about the following will be appreciated:
1) Cat5 cables – are they allowed to carry 1 A ? (they are
typically
24AWG and rated 0.577A)
2) Are you/we going to require same insulation requirements as in
PoE ?
(1500V)
3) Are we talking SELV, TNV1 or we have a new definition we need
to
look for compliance? (such as taking 60950-21 into consideration )
Ilan Cohen,
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