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[802.3af] Communication from UL re Limited Power Source per IEC 60950


The following communication was received via FAX by Geoff Thompson, 1st
Vice-Chair of 802. Geoff very kindly typed it into an e-mail message to me.
I am am forwarding it to the 802.3af Task Force for your review and comment.
I would like to suggest that the group set up an ad hoc to examine the
technical questions raised in the memo, and that you all request an opinion
from your safety standards groups. Issues regarding 802 procedures will be
addressed by the 802 officers, and a reply with be sent to UL. We have
indicated to UL that they are welcome to make further comments at Sponsor

I believe that the specifications in 802.3af describe a Limited Power Source
(LPS) as defined by IEC60950. It may be that a footnote in the draft will be
sufficient to make this clear. I do not believe that it is within our scope
to specify the type of enclosure material that a product must use.

I welcome your comments and insights.



Steven B. Carlson
Co-Chair, ESTA Control Protocols Working Group
Chair, ESTA ACN Task Group
Chair, IEEE 802.3af DTE Power via MDI Task Force
Secretary, IEEE 802.3 CSMA/CD Working Group
High Speed Design, Inc.
11929 NW Old Quarry Road
Portland, OR 97229
FAX 503.626.4206

June 22, 2002

Paul Nikolich
Chair  -  IEEE 802, LAN/MAN Standards Committee

Correlation of IEEE 802 Standards with the IEC/UL ITE Safety Standard 60950

Dear Mr. Nikolich:

On behalf of the UL's Standards Technical Panel (STP) for UL 60950 and the
Information Technology Industry (ITI) Council's Technical Regulations
Committee TC2 on Product Safety, Underwriters Laboratories would like to
initiate some dialogue on the above subject with the IEEE 802 LAN/MAN
Standards Committee.


The present U.S. and Canadian bi-national standard for Safety of Information
Technology Equipment (ITE) is CSA/UL 60950.  This standard is harmonized
with the international (IEC) standard of the same name, IEC 60950.

A variety of ITE is certified for safety to this standard, many of which use
interfaces designed around the IEEE 802 series of standards.  Manufacturers
of both base equipment (e.g., power sourcing equipment) and peripherals
(e.g., powered devices) seek safety certification to IEC/UL 60950.

From a certification standpoint, the application of IEC/UL 60950 to a
complete system of interconnected equipment submitted for certification
works quite well because the characteristics of the entire system are known
at the time of certification.  However, when individual certifications are
requested for parts of the system (e.g., certification of IP phone powered
by an IEEE P802.3af media dependent interface (MDI)), the process is not so
simple because assumptions have to be made about the MDI.

This is where the correlation of the IEEE and IEC/UL standards becomes
vitally important.


IEC/UL 60950 requires that ITE have a fire enclosure unless the source
supplying the power is a Limited Power Source (LPS) as described in
sub-clause 2.5 of the Standard. There are specific voltage, current and VA
criteria associated with the definition of a LPS.

Generally, if thermoplastic, a peripheral's fire enclosure must be V-1
(vertical flame tested) material, which is a material with specific burning
characteristics when subjected to a 20 mm vertical flame.  Thermoplastic
enclosures/casings not designated a fire enclosure by IEC/UL 60950 - e.g.,
supplied by LPS - are permitted to use HB (horizontal flame tested)
materials, which are a less onerous set of flammability requirements from a
safety perspective.  Typically, there are considerable cost savings to the
manufacturer in using an HB versus V-1 material so manufacturers seek ways
to use HB materials.

Although IEEE P802.3af remains a draft standard, peripheral manufacturers
(e.g., IP phone) already are approaching UL and proclaiming that since
these peripherals are connected to an IEEE P802.3af MDI, UL should assume
they are connected to an LPS by nature of the IEEE P802.3af requirements for
PSE outputs (e.g., Table 5).  Therefore manufacturers believe such
peripherals do not need a fire enclosure.

However, based on our review of the draft IEEE P802.3af standard, UL has
concluded that broad assumptions cannot be made about this MDI and its
compatibility with IEC/UL 60950 LPS requirements since there is no direct
reference to LPS requirements in IEEE P802.3af for power sourcing equipment.
Therefore, the present UL position is that peripherals that are individually
certified (e.g., UL Mark on peripheral) and powered by an IEEE P802.3af MDIs
require a fire enclosure.  Obviously, peripheral manufacturers are not
satisfied with this certification decision.


UL hopes that the present situation presents an opportunity to start
dialogue between the IEEE LAN/MAN Committee and the product safety sector of
the ITE Industry.  In particular, we recommend that when IEEE is developing
new MDI and similar documents, consideration be given to
assuring that product safety professionals are included on the respective
committees.   While we acknowledge that there already exists representation
from ITE manufacturers on the Committee, additional effort is needed to make
sure parties intimately familiar with IEC/UL 60950 and Industry safety
certification practices are represented.  Hopefully, with the proper
representation those parties familiar with the relevant safety issues would
include specific references to particular IEC/UL 60950 requirements (such as
LPS) in the IEEE documents rather than just mentioning IEC/UL 60950.
Experience has shown that simply referencing a safety standard does not
necessarily provide the proper design guidance to manufacturers with regards
to this type of issue as they design products to the IEEE

Several years ago we had a similar experience with the IEEE 1394 and USB
specifications. Eventually UL was able to make some general assumptions
about these busses being LPS when the IEEE and USB specifications were
modified to specifically mention the need for them to be LPS, e.g.,
of IEEE 1394a.

We have also attached an extract (agenda item 6) from our published Meeting
Report for the April 2002 UL 60950 STP Meeting.

We are interested in hearing your thoughts on the subject and thank you in
advance for your time.

Best regards,

Thomas M. Burke
Principal Engineer
ITE Lateral Business Unit
Underwriters Laboratories Inc.
1655 Scott Blvd
Santa Clara, CA 95050
Direct Phone: 408.876.2286
Fax: 408.556.6056
Email: Thomas.M.Burke@xxxxxxxxx
Web Site:

Kevin L. Ravo
General Manager
ITE Lateral Business Unit
Underwriters Laboratories Inc.
1655 Scott Blvd
Santa Clara, CA 95050
Direct Phone: 408.876.2311
Fax: 408.556.6174
Email: Kevin.L.Ravo@xxxxxxxxx

Web Site: