[j-nsp] MX480 DC Power

Matt Yaklin myaklin at g4.net
Wed Mar 18 13:48:21 EDT 2009

On Wed, 18 Mar 2009, Ernie Rubi wrote:

> Thanks, a quick read makes it look like we need 4 DC feeds to the router in 
> order to have it be redundant.
> We have only an A+B feed, so only 2 out of the 4 needed.
> If I operate this way, the power supplies won't be redundant?
> Also, what other info would you need to fully answer the question?  We are 
> going to be running 2 x 10GE as well as 6 GigE interfaces on a DPC line card 
> plus redundant RE-2000s.

Please keep in mind that I do not have a MX480. I own other Juniper

The missing information to me was the amount of power supplies.
I also understood the pdf as saying if you wanted 4 power supplies
you would need 4 feeds with each feed having 32 AMPs @ -48 VDC.

The back contains 4 power supply slots. PEM0-3 they are called.
If you only have two power supplies you need to insert them in PEM0
and PEM2 for example** (See below). If one fails you are down.

With 4 power supplies you can have one each fail among PEM(0-1) and
PEM (2-3). But if PEM(0-1) both fail you are down. This all assumes
you are running a fully loaded chassis***(See below).

Here is a pdf to help you out:


**I am also not sure if the manual has a typo under "DC Power Supply
Configurations for the MX480 Router" where it states, "If only two DC
power supplies are installed, they must be installed in slots PEM0 and
PEM1 or in slots PEM2 and PEM3." That really does not make sense to me
if you look at Table 1 and how they back each other up.

***Notice how the DPC slots 0 and 1 are powered by PEM(0-1) and
DPC slots 2 through 5 and powered by PEM(2-3).

I hope this helps.


> Ernie
> On Mar 18, 2009, at 1:06 PM, Matt Yaklin wrote:
>> Here you go:
>> http://www.juniper.net/techpubs/en_US/release-independent/junos/topics/reference/specifications/mx480-power-components-dc.pdf
>> It seems it is hard to answer your question straight away as
>> we do not know enough information.
>> I hope that link helps.
>> matt
>> On Wed, 18 Mar 2009, Ernie Rubi wrote:
>>> Hi folks,
>>> I currently have a -48 vDC, 2 phase (A+B) 70 Amp (total) DC circuit.
>>> I need to order an MX 480 with DC power, will the DC circuit that I 
>>> currently have work?
>>> Thanks,
>>> Ernesto M. Rubi
>>> Sr. Network Engineer
>>> Florida International Univ, Miami
>>> Reply-to: ernesto at cs.fiu.edu
>>> Cell: 786-282-6783
>>> _______________________________________________
>>> juniper-nsp mailing list juniper-nsp at puck.nether.net
>>> https://puck.nether.net/mailman/listinfo/juniper-nsp

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