Re: [8023-POEP] Cabling and wire current capacities
Folks
It was a MAJOR goal of 802.3af to produce a power standard for Ethernet
that would skate under the radar of all safety standards on a world-wide
basis.
To the best of my knowledge we succeeded and have not been challenged by
any of the regulatory bodies or standards with regard to the current
standard.
This significantly simplifies the hardware qualification process.
There has been precious little mention of this as either a consideration
or a goal in PoE Plus.
Per Steve's discussion below and Mike's steam pipe example in the
meeting, there will be plenty of installation opportunity for abuse and
failure. This whole area badly needs the focal topic of discussion rather
than what will work wrt temperature rise in a "good"
installation.
I believe it continues to be our expectation to provide power "over
existing cabling" (though this is still up for discussion). That
means the initial acceptance and functionality test for the cabling will
not prove the suitability for safely adding power.
If we do not squarely face this problem we set ourselves up for both
failing on this project but polluting the success of 802.3af.
Geoff
At 07:07 PM 1/31/2005 -0800, Steve Robbins wrote:
Guys,
This is just a suggestion, but
instead of consulting NASA specs, I would ask UL (Underwriters Lab) or
some other group whose opinion will count when it comes to fire
safety. (I spent many years working on the electric power system
for the international space station, and don't have a lot of trust in
specs written by those "rocket scientists" at NASA.)
Here's what makes me a bit
nervous about the ampacity discussions I've been reading in these
emails: One of the great things about PoE is that it's the first
international power standard, but one of the scary things is that it's
the first power standard where most hook-ups will be done by some Joe
Blow IT guy instead of a licensed electrician. There will be people
using cables that are not in the best of condition, hanging them over
sharp metal edges, hanging them near heat sources, tying them into large
bundles, doing bad crimp jobs, hooking them into patch panels with loose
screws, etc. There will be plenty of instances where something is
getting a lot hotter than you expect. All it might take is a few
small fires scattered around the planet for big insurance companies to
start putting clauses in their policies for corporate customers
prohibiting the use of PoE in office buildings. That would be the
end of this technology.
I'm sure that SAE or MIL
standards will be useful as guidelines. But when it comes to safefy
in electronics, people look for the UL or CE marks on products, not NASA,
SAE or even the IEEE. I don't know if UL or CE have specs for wire
ampacity, but I'd feel better if I knew they were part of the
discussion.
Anyway, that's my two
cents. Sorry if it seems alarmist. I just think we should be
very conservative about ampacity. More conservative than
organizations who might have effective veto power, such as big insurance
companies.
Steve
Robbins