PoE per port limitation

SOLVED
AndreasKvist
Getting noticed

PoE per port limitation

Hi, 

 

I´m wondering if there are any limitation when powering APs MR42E with a MS120-24p.

 

The MR42E requires 20W and the MS120-24p has a poe budget of 370W. 

 

This would suffice if there is no Watt limit on the ports so that one specific port can´t deliver more poe than up to a cirtain level. I have found poe budget documents but nothing about limits the ports. 

 

Just wanted to make sure that the choosen switch is not to weak. 

 

I have been looking at MS120-48fp that has poe+ and 740W.

 

Thanks 

 

BR

 

Andreas

 

 

1 ACCEPTED SOLUTION
merakichamp
Building a reputation

@AndreasKvist   The IEEE 802.3at (PoE+) standard supports up to 25.5W of power on the ports, allowing devices that require more than 15.4W to power on when connected to the PoE+ ports.

 

hope this will shade some light    PoE Support on MS Switches

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5 REPLIES 5
merakichamp
Building a reputation

@AndreasKvist   The IEEE 802.3at (PoE+) standard supports up to 25.5W of power on the ports, allowing devices that require more than 15.4W to power on when connected to the PoE+ ports.

 

hope this will shade some light    PoE Support on MS Switches

Thank you! That what exactly what I was looking for. MS120-48FP it is. Have a great day onwards.

BR

Andreas

@AndreasKvist  you are most welcomed

 

MerakiDave
Meraki Employee

@AndreasKvist you are going through the correct exercise around PoE budgetary planning, I just wanted to add the reminder that the MR42E 20W figure is definitely a maximum, and on average might only need half that much power.   

Stealing from an old post I made, go to the Switch > Switches page and click into the switch and click on the power tab.  You will see a "Consumption" section and a "Budgeted" section.  The number to worry about is the consumption. The budgeted number is just reflecting the total amount of theoretical power that could be consumed, as if every device pulled the full 15 or 30 watts of power it advertised via CDP/LLDP when it first negotiated.

 

See screen shot below.  I have a compact MS220-8P switch running 7 PoE devices all the time (MV cameras and MR APs).  Looks at my "Budgeted" section, it says 140W/124W.  That's showing that the switch max budget is 124W of PoE power, and those 7 devices (at max power draw) would take 140W.  That's because 2 of my devices are an MV72 and an MR52 both of which negotiated 30W, and the other 5 devices negotiated 16W, so there's the 140W number.  It rounds 15.4W to 16W when doing this to err on the conservative side. 

 

But notice the consumption tends to hover around 41 to 45 watts.  Will that fluctuate?  Sure.  I don't watch it that closely, but I've never seen it over 60 watts, not even halfway to the max the switch can deliver.

 

MS220-8P-Power (1).jpg

Hi Dave, 

 

I think then there should be a note in the datasheet regarding maximal consumption vs general consumption specially if it is an absolute maximum value. 

 

From the installation guide. 

https://documentation.meraki.com/MR/Installation_Guides/MR42E_Installation_Guide

The MR42E will function in low power mode when powered by a 802.3af power source. While in low power mode, the MR42E will disable its Air Marshal radio as well as two out of three transmit streams on the 2.4 Ghz band. Despite being in low power mode, the device can still supply full 802.11ac capabilities. 

 

BR

 

Andreas

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