We are about to install our first server and networking rack at my office. I'm more of a programmer than a sysadmin, so I'm learning as I go. Let me start by saying that it's just a router, patch panel, and PoE switch that will be going on the rack initially. Servers will be added letter.

I need advice on how power should be distributed to the rack. We use APC UPSes for most of the equipment in our office, and I know that APC makes rack-mount models. However, I've also seen PDUs and vertical power strips, and I'm not sure which approach to take, or when mixing-and-matching is appropriate.

The vertical power strips that mount to a cable organizer look like an attractive option, but since these don't offer anything in the way of surge protection or battery backup, it seems like they would have to be plugged into a UPS, and it also seems like I remember that this is a big taboo.

Basically, I'm wondering which of these are "correct" and which are wrong:

(1) Power Outlet --> UPS --> Rack Equipment

(2) Power Outlet --> UPS --> PDU --> Rack Equipment

(3) Power Outlet --> UPS --> Vertical Power Strip --> Rack Equipment

Thanks in advance for your help.

  • Thanks for the pointers, everyone. I'll probably going with option #1 to begin with, but for future reference I just want to be certain: Is it okay to plug a power strip into a UPS? Or vice versa?
    – Jon
    Sep 17, 2010 at 17:28
  • Technically, it's not recommended to plug a power strip in to a UPS and is probably terribly unsafe. In reality, people do it all the time and I've yet to hear of a problem caused specifically by that as opposed to overloading the circuit. You can purchase PDUs, which are specifically designed for adding outlets, just make sure you don't go over the recommended watts/VA/etc.
    – David
    Sep 21, 2010 at 0:13

5 Answers 5


I'd go with 1 to start off with.

The UPS should have enough outlets for your needs right now and less stuff = less problems.

  • less stuff can also mean more downtime later to add in more stuff.
    – Chris
    Sep 17, 2010 at 17:26

We normally go with option 2 and purchase PDUs where you can control the outlets individually (called switched/smart/intelligent PDUs). That means if a server locks up, you can log in to the PDU and power cycle it remotely.

If you don't plan on needing to remotely reboot the power on servers, I would say go with option 1 until you run out of power outlets, then switch to option 3.

The other question you have to ask yourself is what kind of power can you get in your office. That will determine the type of UPS you can get.

Based on the small amount of equipment you're installing, having 110v (over 208v) power is probably fine, but if you want any kind of decent UPS battery life, you're going to need to install a special outlet (most likely L5-30). Pay attention to the "Input Connections" line on the Technical Specifications pages of APC UPSes.


APC's PDUs go from fancy power bar to fully managed power bar...

The basic model is just a high grade power bar that you mount in your rack. The higher end ones have web pages where you can monitor power usage and have it send SNMP data for power usage reporting. The highest models allow you to turn on and off specific power ports in case you need to reboot a machine, save power, or mess with the sales guys.

One of my clients has servers hosted in a 3rd party data center, the power is battery backed, but we never knew how much current our servers were drawing, on more than one occasion we tripped breakers and lost a rack.

Getting the PDUs that allow us to monitor our usage and having it report via SNMP lets us know what racks we can add equipment too or if we need to shuffle equipment around.

Since you are looking at having just one rack and you will have your own UPS I don't see any reason for you to get the high end PDUs, all this information is available on the UPS. However, if you do need additional sockets a low end APC PDU is, IMO, much better than a power bar.


The only sure rule is always use a UPS between your equipment and anything else (power strip or outlet). I'm not sure what you mean by a PDU in this case. A "PDU" is a Power Distribution Unit, which tends to indicate a fuse panel in rack environments (at least in the 100+ data centers and COs I've worked in). Usually I only see those in DC environments. You can get surge protected rackmount power strips for 19" racks, and those are nice, simply for routing the power cables (you only have one leaving the rack, the rest can be tied in or managed on the rack in a neat manner). A common setup is to have all the equipment plugged into one or more UPS devices on a shelf at the bottom, and then have all the UPS devices plugged into a rack mounted strip, and then the strip going to the wall.


I don't know if anyone has mentioned it, but you shouldn't plug power strips or PDUs into the smaller APC units. Even some of the bigger rackmount APCs don't support this.

You should go with:

(1) Power Outlet --> UPS --> Rack Equipment

and nothing else, unless you are sure it is supported by the UPS manufacturer. If there aren't enough plugs on the UPS, you need a different UPS.

  • Where did you come across this? I've never seen anything in the docs to indicate this? Do you have a link?
    – Clint
    Sep 28, 2010 at 16:13
  • Fire Marshall, APC themselves, the electrician. No one in their right mind would recommend plugging a multi-outlet device into another multi-outlet device. Heck, a quick google search turned up another serverfault question around the same thing: serverfault.com/questions/29288/… Sep 29, 2010 at 14:06

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