poe requirements

[mirehteshamali]

Hi all

1)i m using POE to provide power supply for cisco access points .  however they are connected using CAT6 as they are approximately 250 - 350 meters away from the switch .

will the access points get sufficient power , the reason i m asking  is due the distance from the POE capable switch .

2) i m confused at power supplies requrments .

Catalyst 4500 PoE Enabled Power Supplies	PWR-C45-6000ACV=	Catalyst 4500 6000W AC dual input Power Supply (Data + PoE)
	PWR-C45-4200ACV=	Catalyst 4500 4200W AC dual input Power Supply (Data + PoE)
	PWR-C45-2800ACV=	Catalyst 4500 2800W AC Power Supply (Data and PoE)
	PWR-C45-1300ACV=	Catalyst 4500 1300W AC Power Supply (Data and PoE)

is their any guide to help me select proper power supply based on requirments ?

what power supply shoul i select if we have 2 line cards 48 ports , 24 of them require POE  on 4503 swithch ?

3)  is it correct that on every cat 4500 / 6500 one line module will be consumed by supervisor engine ? if we have two supervisor engines for redundancy  will it consumes two line slots ?

4) does fan tray comes with chasis or i need to purchase it seprately ?

thanks

[mirehteshamali]

common guys , questions are not tough

let me know if i m not clear in expressing

thanks.

does poe work on longer distances than usual ie 300-400 mts. ? i have to connect access points to a poe capable sw but at distance longer than cat 5 suports .  appprox 300 mts.

how to determine proper power supply ? do i have to do load calculation , no of line cards , poe connected devices etc ?

when u say 4503 or 4506  it supports 3 and 6 line cards slots respectively . while one line slot is consumed by supervisor engine itself  just want to confirm this ?

when i order for chasis ? does it comes with fan tray else where to find fan tray part no's.

[Peter Paluch · Accepted solution]

Hello,

No need to speed up our answers - most people do not work through weekends.

Regarding the PoE over the distances you want to use it over: you are walking on a very thin ice. You have indicated that you are using Cat6 cabling to span distances over 250m. This is an utmost risky approach. No cabling category is intended to provide cabling in excess of 100m between any two active components. A higher category does not mean you can use longer cable runs. A higher category means better transmission characteristics so that on segments of max 100m, potentially higher transmission speeds can be used and/or the transmission will be less error-prone. However, regardless of the cabling category used, each and every Ethernet device vendor guarantees its reliable operation only on a cabling made according to existing standards, including the max length limits. The fact that your network currently works is, so to say, your lucky bet. It could just as easily stop working or exhibit numerous transmission issues. Should anything go wrong or stop working, the vendor will take no responsibility because you are forcing its device to work outside the conditions it was built for.

Regarding the PoE on such a long cable run: with respect to classic PoE, the maximum power provided by the powering port is 15.4W, however, because of power loss and dissipation in the cabling, the powered device can expect to use only 12.9W. Thus, on 100m cable run, the standard expects to lose as much as 2.5W (I am not sure how they computed it - I've tried to make the computation myself taking the resistance of the copper AWG23 cabling into account but I have arrived at a substantially lower number - obviously there is something more to it). Now, on 300m cable run, you can roughly expect three times the loss, thus, 7.5W may be lost. That would make only 7.9W available to the powered device.

You could argue that the standard was overly conservative in estimating the power loss in the cable. That may very well be true and your devices may be powered over PoE just fine. Then again, there is no guarantee. The problem remains: you are in violation of the standard, and the resulting operating conditions may be very fragile.

Personally, I would not recommend doing it, and instead, I strongly vouch for remaking your current cabling to meet the current standards. My personal opinion is that sticking with twice to thrice the maximum cable length is simply calling for trouble.

Best regards,

Peter

[mirehteshamali]

Thanks peter for a very knowledgeble & well versed answer .

i will use power injector in that case and redesing the network if possibe .

for my second question .

i guess it wont hurt going for a higher power then required  , but still i m looking for any link to arrive at correct power supply . the problem will be when power  requirements are more than the selected power supply .

Thanks once again .

yes no need to answer on weekends , my appologies .