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Old 08-11-2009, 04:08 PM   #1
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Wall Mount Server Cabinet. How much power?


I recently bought these two server cabinets.

http://www.discount-low-voltage.com/wacadusw24in.html

I'm installing them in our building but I'm not sure what to tell the electrician on what my power requirements are going to be. Going to install a switch and a cisco router and a UPS.
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Old 08-11-2009, 04:12 PM   #2
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Wall Mount Server Cabinet. How much power?


That would depend upon the requirements of the items you are installing
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Old 08-11-2009, 04:51 PM   #3
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Wall Mount Server Cabinet. How much power?


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Originally Posted by cochise7969 View Post
I recently bought these two server cabinets.

http://www.discount-low-voltage.com/wacadusw24in.html

I'm installing them in our building but I'm not sure what to tell the electrician on what my power requirements are going to be. Going to install a switch and a cisco router and a UPS.
A single switch/router combination shouldn't use much power at all. However, those are most likely fairly critical pieces of equipment - badness happens if they go down. For that reason, it is common to run individual dedicated circuits for each cabinet. If you wanted to save some money, you could run a single 20A circuit for both cabinets.
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Old 08-11-2009, 08:40 PM   #4
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Wall Mount Server Cabinet. How much power?


Having specified and installed many similar racks and from your equipment description, I would suggest a dedicated 115v 20 amp circuit to each rack. You could use a 15 amp circuit, but I would not as the expence is in the labor not the breaker and wire.
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Old 08-11-2009, 09:01 PM   #5
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Wall Mount Server Cabinet. How much power?


yes, run a dedicated 20 amp circuit to each cabinet. Most cabinet PDUs are rated for 20 amp service.
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Old 08-11-2009, 09:52 PM   #6
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Wall Mount Server Cabinet. How much power?


"a dedicated 20 amp circuit to each cabinet" this sounds like the most important thing to do, I'll make sure this gets done thanks guys.
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Old 08-11-2009, 09:57 PM   #7
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Wall Mount Server Cabinet. How much power?


If they are not soft-start devices you may need breakers with a trip curve that can tolerate the start-up current pulse of the switching power supplies that are inside these things.
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Old 08-12-2009, 12:17 PM   #8
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Why not have the electrician tell you whats required. Hes doing the job.
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Old 08-13-2009, 01:02 PM   #9
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The electrician is a friend of mine and I'm not to sure about his work, things have been slow for him so I was thinking about throwing him a bone.
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Old 08-13-2009, 01:21 PM   #10
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Wall Mount Server Cabinet. How much power?


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The electrician is a friend of mine and I'm not to sure about his work, things have been slow for him so I was thinking about throwing him a bone.
One more very important point: The two dedicated circuits must be separate, not a multiwire branch circuit sharing the neutral. DO NOT SHARE THE NEUTRAL! Make sure he doesn't share the neutral. Normally it wouldn't be a problem, but there are two reasons not to do it here: First, if you're on the 2008 NEC then a double-pole breaker would be required. This would defeat the purpose of running two dedicated circuits - if one trips (or needs turned off for service) the other would go down too. That's bad. Second, if the neutral wire is shared and comes loose, your equipment will burn! Sure, wires don't come loose often, right? I had it happen once, on an installation just like this one. Two dedicated circuits feeding a cabinet with an OC24 line terminated in it, providing the internet connection for a bank's entire transaction processing network. Each circuit fed one of the two redundant power supplies. Neutral got loose in the box, and smoked BOTH power supplies! So much for redundancy. Got to replace both PSUs before the battery backup died!
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Old 08-13-2009, 03:03 PM   #11
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Wall Mount Server Cabinet. How much power?


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if the neutral wire is shared and comes loose, your equipment will burn!
smoked BOTH power supplies!
With a bad neutral the total voltage should stay at 240v so only one side should burn. Maybe the voltage to each side went all over the map and sequentially fried your stuff. Bummer. . .
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Old 08-13-2009, 04:44 PM   #12
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With a bad neutral the total voltage should stay at 240v so only one side should burn. Maybe the voltage to each side went all over the map and sequentially fried your stuff. Bummer. . .
Assuming the failure mode is "shorted" as opposed to "open", both sides will fail in rapid succession. Whichever one is drawing less power will fail first, thus imposing the 240V on the other one, causing it to fail. Switching PSUs almost always fail shorted on overvoltage, because the input filter caps blow or the surge suppression MOVs conduct. If it has internal fuses, they will not blow until the other load on the opposite leg is destroyed, too.
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Old 08-13-2009, 05:23 PM   #13
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Assuming the failure mode is "shorted" as opposed to "open", both sides will fail in rapid succession. Whichever one is drawing less power will fail first, thus imposing the 240V on the other one, causing it to fail. Switching PSUs almost always fail shorted on overvoltage, because the input filter caps blow or the surge suppression MOVs conduct. If it has internal fuses, they will not blow until the other load on the opposite leg is destroyed, too.
Cacading failures!
Had that in my '75 Spitfire, by design it seems. . .

Computer designed stuff also seems to do that, since AI doesn't need safety factors here and there to make up for ignorance and uncertainty.
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Old 08-13-2009, 06:22 PM   #14
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Wall Mount Server Cabinet. How much power?


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but there are two reasons not to do it here: !
3 reasons.

harmonics
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Old 08-13-2009, 07:44 PM   #15
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Most server cabinets like this are running off 220vac, haven't seen many switching power supplies anymore that weren't auto detecting, or at least have a swtich to set 110/220v
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