Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

When getting power cables for servers, there are are various AWG (American Wire Gauge) choices to make. The ones I have noticed are 18 and 14. 14 is thicker so will be a little more stiff. But I am also wondering how I determine if I really need the heavy duty or thicker 14 AWG cables, or if 18 would be fine.

In my particular chase, this is for 6 foot runs from a power strip to servers. The power will be run at 208v single phase. Using this online calculator, it looks like maybe at most .1 volts would be dropped which sounds negligible (assuming copper).

Other there other concerns here, for instance:

  • Maximum rating
  • Bundled temperature (I have vertical PDUs, so doesn't apply to me, but still is this a concern?)

How do I know which AWG I actually need for my server's power cables?

share|improve this question
1  
From a power strip? I hope you mean PDU :) –  MDMarra Nov 30 '12 at 14:34
    
@MDMarra: So as not to be confused with the floor units. From wikipedia, "The term (PDU) may refer to two major classes of hardware power devices; the first and typically the general unqualified term refers to the category of relatively higher-cost floor-mounted power distribution devices which transform one or more larger capacity raw power feeds into any number of lower capacity distributed power feeds .... The second type of PDU is sometimes called a Smart-PDU, Rack-based PDU, Intelligent PDU or simply "Power Strip" by various IT professionals" –  Kyle Brandt Nov 30 '12 at 14:37
2  
The usual IEC C13/C14 connectors are technically 10 Amp rated, so that is likely what calculations will have to be based upon when it comes to formal safety business etc (notice that C13/C14-fed PDUs will usually have a separate fuse or breaker limiting their intake to 10 Amps). In practice, it is unlikely that all devices fed from a PDU will come CLOSE to 10 amps, given your standard PDU will get 13, 16 or 25 amps upstream only ;) - and heating of a cable follows an amps-squared relation, so 1 amp = 1/100 heating of 10 amps... –  rackandboneman Nov 30 '12 at 14:39
    
Please verify any advice given here by people who are not licensed electricians or inspectors (I am not any of these either) yourself. –  rackandboneman Nov 30 '12 at 14:43
    
If in doubt, you can always set up an experiment (take it outside, bundle some cables and load one with a space heater and a few with computers, and measure temperatures... Also, make sure the cables you use are, if they are from the IEC cable grab bag, indeed 18 AWG and not 20-22 AWG that sometimes come with small devices and .. I always throw these out instantly.) –  rackandboneman Nov 30 '12 at 14:45

4 Answers 4

This Wikipedia Article has a nice table that outlines the exact specifications of the different AWG ratings.

The one to look out for is ampacity at various temperatures. Considering the draw of most modern power supplies, I'd imagine that an 18 or 16 would be fine in most cases, but many servers ship with 14s, so that's what I tend to stick with.

enter image description here

share|improve this answer
    
We used 14s, combined with cable arms, that is a bad choice. They end up popping out of the servers even when you velcro them in nice and tight. We are redoing everything with 16 now (Which is thinner). So this is something to keep in mind. –  Kyle Brandt Jun 7 at 17:25
    
But cable arms are for the birds, @Kyle :) –  MDMarra Jun 7 at 18:31
    
I don't like them myself, but I'm usually not the one working in the datacenters, so I leave it up those guys. –  Kyle Brandt Jun 7 at 22:32

DISCLAIMER: This is personal opinion/knowledge from an IT admin, not an electrician.

Wire gauge is chosen for many reasons, but typically for people like us it is based on amperage used/needed. There's probably lots of other reasons/rules, but for you and I that's basically it.

Kyle, you can look here if you haven't already: http://www.powerstream.com/Wire_Size.htm

Also:

enter image description here

share|improve this answer
1  
Doesn't voltage matter as well? –  Kyle Brandt Nov 30 '12 at 14:38
    
@KyleBrandt not really. if it did, the recommendations would be based on kVa or watts instead. it's current that really drives the cable diameter. –  longneck Nov 30 '12 at 14:40
    
Voltage matters more for "flow" (I'm not an electrician sorry). See here: jamestowndistributors.com/userportal/… I know that's only for 12/24 volts but it might help explain voltage and "flow". –  TheCleaner Nov 30 '12 at 14:42
    
I'm curious why this was downvoted. This is a very similar answer to mine which currently has a positive score. –  MDMarra Nov 30 '12 at 14:51
    
@MDMarra - Probably cause I'm not an electrician. Edited post. :) –  TheCleaner Nov 30 '12 at 14:57

Simple rule that allow to choose right wire - "4A through 1 square mm of copper wire". Rule based on Joule's law Q=RI^2. Thinner wires becomes hot, thicker - are unreasonable expensive.

share|improve this answer

Amperage is what is important. Amperage is what does harm to you and or the wire. For such a close wire run (6') the loss will be minimal. But amperage can burn the wire, blow the breaker. Etc..... But higher the voltage means less amperage. A quick example is 120v 20amp allows 12 AWG ( American wire gauge). 208/240 voltage can go down to 14-16 AWG I beleave. My suggestion is, r mindfull of your amps being used for that system.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.