Best practices for power cabling racks in DC

Solution 1:

Horizontal PDUs are a mess -- In my experience there's nothing that can be done to make these neat: You can bundle your cables neatly down the side of your rack, but when you get to the PDU they fan out into a rat's nest.

For vertical ("Zero-U") PDUs you can acquire custom-length power cables (they're available from various suppliers, usually in the same assortment of lengths you can get ethernet cables in - 1' 3' 5' 7' 14' etc.). The cables can then be bundled and tucked into the side of the rack the same way you would with ethernet cables - I use velcro ties to hold mine to the side of the rack so they don't trap server exhaust...

Some other tips:

• Bundle your cables either by branch (if you have A/B power) or by machine.
  (If you have A/B power you can also use different color power cords to distinguish them - e.g. Black/White)
• Label your cables (Either on the plug or on the PDU) so you know what you're unplugging
• Remember to leave designated power points for a crash cart (keyboard/monitor) if necessary.
  (If you do not have an in-rack keyboard/mouse it IS necessary - a KVM or IP-KVM is not always an adequate substitute)
• Don't run your AC power cables on the same side of the rack as your ethernet cables
  (You already seem to be aware of this)

Solution 2:

Buy short power cables. In the US, I buy 1-foot and 2-foot cables and run to the vertical Zero-U PDUs located on the left and right sides of the rear of the cabinet, since the power supplies are usually situation on the left or right side of the server chassis (never center).

I don't bother with server cable management brackets since they restrict airflow and have become clumsier over the past few years. I buy a roll of raw velcro to cut into strips as necessary to secure the power cables. If I need to pull a system out, I remove the power cable and slide the system out, leaving the power cable hanging in place.

Solution 3:

I think you are spot on for the zero-U PDUs. If you have 3-phase power available, I would install one of these on each side of the rack: http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=AP7892

(208V output is also available but not with 42 connections).

Then connect each server to the appropriate numbered outlet with short power cables. In fact, you can shorten the .5m cables even further by folding them over and using zip ties. Then connect the left power supply to the left PDU, and right to right. For single power supply servers, just alternate between left and right.

With this method, no power cables are ran down the sides of the rack and you don't interfere with your Ethernet cabling.

I would avoid any horizontal PDUs in the rack because they just get in the way of the rest of your equipment.