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Re: [802.3_4PPOE] IEEE 802.3 liaison letter to NFPA CMP 16 in respect to Power over Ethernet


In my opinion there is fundamental flaw in your proposal, in that  you are mixing low voltage Class 2 requirements and current carrying capabilities of small gauge Ethernet cables. While it is true that a 60V 1.5A, or 30V 3.3 A  qualify as a Class 2 power levels, not all  not all Ethernet cables can support that power without exceeding their rated operating conditions, mainly temperature  limitations on the insulation cable.  As with any other cables/wires used in building construction NEC requires that these cables/wires do not exceed their temperature limits under expected operating conditions.

I agree with your proposal to reference Table 11(B) when it comes to 840.160 (A) - Power Limitations. However when it comes to 840.160(B) - Ampacity, there needs to be a table that provides guidance as to what current is permissible based on the wire gauge. The current limits should be per conductor, not a pair of wires as some have suggested during the BICSI WG meeting. The table also needs to address cable bundles, as there is definite contribution from adjoining cables to the overall temperature of the conductors that end up in the center of the bundle.

The rated ampacity in the table needs to be based on 30C ambient temperature and 60C cable rated insulation (most common commercially available), with provision to allow for increased or decrease in ambient temperature where these cables are installed. Similarly, there are cables on the market that are rated for higher operating temperatures (70C, 80C, etc.). There needs to be provision for being able to adjust permissible current  levels to match those higher insulation temperature ratings. Article 310.15(B)(2) has formula that can be used to adjust for ambient temperature, however there is no convenient formula for adjustments to address higher wire insulation rating. We may need to develop formula or add ampacity ratings in the table for multiple insulation levels.

Lastly, adding Informational Notes in the code is just that, information. It is not binding nor is it enforceable in the field. It is simply there for information purposes that can aid in clarifying intent of the code requirement. No installer or AHJ in the field will take time to look up those reference documents, especially if they have to go out and purchase them. 


Don Miletich
Regulatory & Compliance Engineer V | Lighting
Office: 262.884.3180 | Mobile: 262.902.7840 | Fax: 262.504.5429

-----Original Message-----
From: Shariff, Masood [mailto:mshariff@xxxxxxxxxxxxx] 
Sent: Tuesday, August 18, 2015 3:01 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] IEEE 802.3 liaison letter to NFPA CMP 16 in respect to Power over Ethernet

Hi Chad,

I submitted the attached contribution to the BICSI Codes working group that is meeting every Tuesday from 11 am to 1 pm Eastern till Sep 15, 2015.

I would like members of IEEE 802.3bt to please review the attached proposal as the starting point for an IEEE 802.3 public input ( PI) comment to NEC NFPA 70 Code Making Panel 16.  The thinking behind this contribution is to use the same Table 11(B) in the 2014 code to derive the  voltage requirements for the PSE ( engine) and the ampacity requirements for the cabling ( transmission) so the two are compatible and consistent with each other. 

I will be happy to take input from the task force and refine this proposal, re-circulate,  to reach consensus at the September meeting in Bonita Springs. Thx.

Best regards,


-----Original Message-----
From: Chad Jones (cmjones) [mailto:cmjones@xxxxxxxxx]
Sent: Friday, August 14, 2015 12:26 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: [802.3_4PPOE] IEEE 802.3 liaison letter to NFPA CMP 16 in respect to Power over Ethernet

All, please see below. We have been directed by Tom Moore to use the public comment process. Therefore, we have the action item of generating text suitable for submission through the NFPA comment process at the September Task Force meeting in Bonita Springs.

Chad Jones
MGR, HW ENG, Cisco Systems
Chair, IEEE P802.3bt 4PPoE Task Force

>-----Original Message-----
>From: Law, David
>Sent: 01 August 2015 00:23
>To: IEEE 802.3 Working Group <stds-802-3@xxxxxxxx>
>Subject: IEEE 802.3 liaison letter to NFPA CMP 16 in respect to Power 
>over Ethernet
>Dear Colleagues,
>When I sent the IEEE 802.3 liaison letter to NFPA CMP 16 in respect to 
>Power over Ethernet 
>mSrR6H3SFx99cmAz8lg&e= >715 .pdf> I was directed by Tom Moore, Chair, NFPA NEC CMP 16, to use their public comment process. Based on this response I saw two options, either I submit the letter verbatim through the public comment process, or request that the IEEE P802.3bt Task Force to develop text more suited to be submitted through a comment process.
>I have decided to do the latter and will request that the IEEE P802.3bt 
>Task Force develop the text at the their September interim meeting. The 
>IEEE 802.3 Working Group will then have the opportunity to consider the 
>text at the IEEE 802.3 Interim meeting on the evening of Thursday 17th 
>September in time for the public review deadline for online submission 
>of 25th September.
>Best regards,
>  David