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I have a rackmount UPS. The UPS has a 6ft long 12AWG thick power cable that powers it from one of the server room's 20A wall plugs.

The current orientation of the cabinets is not ideal. All but this one are easily moved, however this cabinet's UPS' cable is too short to reach one of the 20A circuits if I were to move it.

Is it acceptable to attach the UPS's power cable to a thick (12AWG? or thicker?) extension cable? I'm no electrical engineer, but I think this will add impedance at the two cable's junction (ie. the plugs). I don't know if I should worry or not. Having an electrician come out and re-due the cable on the UPS is really not an option.

I know people generally don't recommend daisy-chaining surge protectors (even though it will work for most cases), but surge protectors are doing a bit more than just a plain cable.

(please don't just say "no don't do this!", please explain why, the risks, pros and cons.)

SnakeDoc
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    Great question. The pragmatic part of me says that, assuming you use a high-gauge cable, it shouldn't be a problem. The other side of me says, though, that this is something that the fire marshall might get upset about. Of course that's locale-specific. Looking to hearing other answers... – EEAA Mar 28 '14 at 15:12
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    Electrically it's fine. Fire code wise, probably not. Most don't allow permanent use of an extension cord for a device that gives more outlets (or something to that effect...consult your local fire marshal). The fines can be quite stiff. – Grant Mar 28 '14 at 17:26
  • The way around the 'extension cord' rule is to simply open the UPS, and replace the cord with one that is not only the correct length, but also gauge. – Lee Harrison Mar 28 '14 at 17:52
  • @Grant funny, I don't think the local fire marshal has ever asked to see inside the server room, or if they even know about it! They usually just check fire extinguishers, and our fire room (with alarms, fire suppression system controls, etc). (Not that I'm advocating breaking the fire code). -- If I'm understanding you correctly (and supplemental research) I need to use a 12/3 AWG cable preferably with a connection coupler lock (to prevent the cables from coming apart accidentally). I guess I also need to figure out if the fine is more costly than hiring an electrician for another 20A circuit – SnakeDoc Mar 28 '14 at 18:38
  • @LeeHarrison this would be a good suggestion, however it would mandate down-time and I don't think I'm qualified to do that type of electrical work (my experience soldering circuit boards is much different than soldering a 20A electrical connection). – SnakeDoc Mar 28 '14 at 18:42
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    @snakedoc on some UPS models you can get a replacement power cable, possibly a longer one - it would only require a few minutes downtime, and no soldering, you just open the unit and clip it in. Contact the UPS manufacturer to see if that's an option. If you do end up with an extension cable, you definitely want a locking one. And to make sure that joint isn't a tripping hazard. – Grant Mar 28 '14 at 19:45
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    @SnakeDoc Also, even if the fire marshal doesn't inspect it...he will if there is ever a fire. And he'll notice the cable then. Whether or not that's the cause of the fire, your insurance company might decide it invalidates your insurance. – Grant Mar 28 '14 at 19:47
  • @Grant that is a good point re: fire fallout. Also, I guess I'll investigate the replacement clip-in cable... it's an APC unit... but I'm unsure. – SnakeDoc Mar 28 '14 at 20:06
  • I just checked with APC, this unit does not have a replaceable power cable. Their suggestion was to buy a new unit (of course! ;-P). They did say the extension cable may cause the unit to trip over to battery... although I couldn't get a straight answer as-to why. – SnakeDoc Mar 28 '14 at 20:21
  • @snakedoc if you can't get a replacement cable do not try modufying it yourself. Changing the cable to a non apc provided one likely invalidates its UL listing which again has insurance implications. – Grant Mar 28 '14 at 20:47
  • @SnakeDoc the reason the unit would trip to battery is explained in my answer. The voltage and amperage may fluctuate depending on the length of the cable. If the voltage drops a certain amount the unit would kick to battery power. Modifying equipment like this that is in a production environment is NEVER recommended as the results could be devastating. At this point since you contacted APC and received that answer I'd say it's time to call an electrician or purchase a unit with a longer cord. – Mike Naylor Mar 31 '14 at 13:01

1 Answers1

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There are a lot of things that prevent a direct answer to this question and should be considered before doing this:

  1. Fire codes in your area
  2. Regulatory requirements on your datacenter
  3. Warranty coverage by your UPS vendor
  4. Length of the extension and proper load calculation to prevent fire hazards

Personally I would HIGHLY recommend either of the following:

a) Contacting a licensed electrician to install a second 20A circuit closer to this location

b) Contacting the vendor of the UPS before using ANY type of extension or piggy-backing the UPS off another unit

As a side note: depending on the length of the cable needed, using a 20A rated cable to run a 20A rated appliance may not be what is needed. If it is a longer run you may need a heavier cable to provide the proper current without posing a threat to deterioration of the wire due to heat or worse, a fire. There are Calculators online to calculate wire sizes needed to deliver x Amps over y Distance at z Volts. I'd highly recommend researching this before using ANY extensions on this project.

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Mike Naylor
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