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Mellow 08-13-2012 04:34 PM

Installing outlets for a server
 
I have a home based server rack that at peak needs a lot of amps.
I have divided all the servers and equipment into three groups and then added up each items actual amp draw. All is 120VAC.

Group 1 - 14.6 AMPS
Group 2 - 19.5 AMPS
Group 3 - 12 AMPS

So I need three 20 AMP outlets. I can shift a few things to bring the 19.5 AMPS down to about 15 AMPS to leave some room.

This would be at peak use and maybe a little higher for a few seconds at start up. This is not calculating any "head room" for expansion though I do not envision any.

I do have a 8AWG 30AMP 120VAC line (for RV outlet outside) that runs right over the server rack but I found out there is no 30AMP outlets, only 20AMP

My questions are:
Do I install three 20amp breakers run three lines to three 20AMP outlets?
Can I pigtail off the the 8AWG 30AMP line with 12AWG wire to two 20AMP outlets so then I just need to run one new 20AMP service.
What about a 40 amp breaker with one line into a three 20AMP outlets with heavy enough AWG?
What is a 20AMP double pole breaker used for?
Any recommendations?

Thanks!

kevinp22 08-13-2012 04:52 PM

Run 3 20A circuits using #12 wire

Bring group 2 down to 16 amps by moving to group 3 some items. breakers are designed to run continuosly at 80% of their rated value.

30A, 40A and 50A rec exist but not for general purpose receptacles (the server racks probably specify using a 15A or 20A dedicated circuit). they are for things such as stoves and dryers.

Provide full house surge protection and surge protection on each circuit (point of use)

2 pole 20A breakers are for 240V circuits or for a multi-wire branch circuit. Since you need 3 circuits, run 3 separate ones with 3 separate 20A breakers. (If you only needed 2 circuits a MWBC might be a consideration)

kevin

Mellow 08-13-2012 05:02 PM

Quote:

Originally Posted by kevinp22 (Post 987707)
Run 3 20A circuits using #12 wire

Bring group 2 down to 16 amps by moving to group 3 some items. breakers are designed to run continuosly at 80% of their rated value.

30A, 40A and 50A rec exist but not for general purpose receptacles (the server racks probably specify using a 15A or 20A dedicated circuit). they are for things such as stoves and dryers.

Provide full house surge protection and surge protection on each circuit (point of use)

2 pole 20A breakers are for 240V circuits or for a multi-wire branch circuit. Since you need 3 circuits, run 3 separate ones with 3 separate 20A breakers. (If you only needed 2 circuits a MWBC might be a consideration)

kevin

Thanks Kevin!

Not wanting to cut any corners but can I pigtail off the over passing 8AWG 30AMP(breaker) 120VAC line (RV outlet outside) with a 12AWG wire to a 20AMP outlet so then I just need to run two new 20AMP lines?

kevinp22 08-13-2012 05:06 PM

No, you cant. For one, 12 AWG wire can only be protected by a 20A breaker or less. Second, even if you ran #8 or #10 all the way, the receptacle will only be rated for 20A

Even if you could or if you dropped the RV cuircuit 20A [Not sure that would even be legal - out of my area of expertise], you dont put delicate server equipment on the same circuit as an RV or any other large appliance.

Kevin

andrew79 08-13-2012 05:06 PM

They make power strips for server racks that do all this for you. Spend some time on google. It may make your life easier

stickboy1375 08-13-2012 05:13 PM

Quote:

Originally Posted by kevinp22 (Post 987707)
breakers are designed to run continuosly at 80% of their rated value.

)

kevin

The servers do not qualify as a continuous load.... you can max out each breaker at 20 amps.

kevinp22 08-13-2012 05:17 PM

Stick,

Under Code I can see they would not qualify. But in reality, wouldnt they run 24/7?

BTW, I should not have used the word "continuous" in my post since it has specific code meaning. It is my understanding that if a 20A circuit runs at 19.5 amps for hours, days, etc, depending on certain factors, it will eventually trip. If Im wrong sorry for the confusion.

Kevin

stickboy1375 08-13-2012 05:20 PM

Quote:

Originally Posted by kevinp22 (Post 987738)
Stick,

Under Code I can see they would not qualify. But in reality, wouldnt they run 24/7?

BTW, I should not have used the word "continuous" in my post since it has specific code meaning. It is my understanding that if a circuit runs at 19.5 amps for hours, days, etc, depending on certain factors, it will eventually trip. If Im wrong sorry for the confusion.

Kevin

A server is never going to work continuously for 3 hours or more, they ramp up and down, thus not meeting the criteria of the definition of continuous load...

And no, a 20 amp breaker will not trip at 19.5, they would run at 21 amps for infinity, 25 amps in an hour, 30 amps for minutes, its all in the trip curves, and this is all acceptable and tested by UL...The UL standard permits an OCPD to carry 134% of the device rating forever. It has to trip in no more than 60 minutes for 135% load.

curiousB 08-13-2012 05:30 PM

I would think cooling the room is the bigger problem. 46A @120VAC is 5,500 watts of heat.... that requires 18,766 BTU (1.6 Tons) of (sensible) cooling to eliminate. Most A/C units BTU rating is the sum of latent and sensible cooling so you need to derate the label to get only sensible cooling to stack up against the 18,766 BTU load. Latent cooling is dehumidification and not useful for extracting BTU in a computer room.

Mellow 08-13-2012 08:34 PM

Quote:

Originally Posted by andrew79 (Post 987729)
They make power strips for server racks that do all this for you. Spend some time on google. It may make your life easier

Two of the groups go to a rack mountable power strip / surge arrest (20AMP) of their own and the third group of main servers to an UPS.

I am not sure what you meant "They make power strips for server racks that do all this for you." The power requirements stay the same power strips or not. If there is something in specific you think might work better please let me know.

Mellow 08-13-2012 08:48 PM

To be a bit more specific about the rack...

There is
1 routers
1 switch
1 Keyboard/monitor
Top fan unit (6 fans)
4x HP DL360 G4
5x HP DL360 G4p
1x HP DL360 G5
1x HP ML370 G4
Hard Drive / Tape Drive Backup unit
APC UPS
2x power strips

All the servers are loaded with dual quad core processors, full RAM and all bays loaded with hard drives.

This network is what is know as a render farm. I do computer animation and when it comes time to render out all the frames of a project the servers work togeter as one rendering each frame (27 frames per second). So really only 2 of the servers are on 24/7 the rest only goes online when there is a render job but at that point I do need the 3x 20AMP outlets. Currently I am running heavy duty extension cords all over the place.

It looks like I am installing 3x dedicated 20AMP breakers, 3x #12 wires, 3x 20AMP outlets. I have one blank left in my panel so I guess I will be installing skinny breakers. Luckily the breaker panel is only about 15' from the server.

Mellow 08-13-2012 08:52 PM

Quote:

Originally Posted by curiousB (Post 987755)
I would think cooling the room is the bigger problem. 46A @120VAC is 5,500 watts of heat.... that requires 18,766 BTU (1.6 Tons) of (sensible) cooling to eliminate. Most A/C units BTU rating is the sum of latent and sensible cooling so you need to derate the label to get only sensible cooling to stack up against the 18,766 BTU load. Latent cooling is dehumidification and not useful for extracting BTU in a computer room.

You are right, cooling is an issue. What does count in my favor is the fact that not all the servers run 24/7 (see post above) it is also located in a cool relatively dry basement. I do have a window AC unit and together with the six top rack fans it does an OK job to keep the room around 80 degrees depending on the ambient temperature.

stickboy1375 08-13-2012 08:52 PM

Quote:

Originally Posted by Mellow (Post 987894)
To be a bit more specific about the rack...

There is
1 routers
1 switch
1 Keyboard/monitor
Top fan unit (6 fans)
4x HP DL360 G4
5x HP DL360 G4p
1x HP DL360 G5
1x HP ML370 G4
Hard Drive / Tape Drive Backup unit
APC UPS
2x power strips

All the servers are loaded with dual quad core processors, full RAM and all bays loaded with hard drives.

This network is what is know as a render farm. I do computer animation and when it comes time to render out all the frames of a project the servers work togeter as one rendering each frame (27 frames per second). So really only 2 of the servers are on 24/7 the rest only goes online when there is a render job but at that point I do need the 3x 20AMP outlets. Currently I am running heavy duty extension cords all over the place.

It looks like I am installing 3x dedicated 20AMP breakers, 3x #12 wires, 3x 20AMP outlets. I have one blank left in my panel so I guess I will be installing skinny breakers. Luckily the breaker panel is only about 15' from the server.

I bet when you are all said and done and ever installed an amp probe, you would be in disbelief of the actual amperage drawn... :)

Mellow 08-13-2012 09:10 PM

Quote:

Originally Posted by stickboy1375 (Post 987898)
I bet when you are all said and done and ever installed an amp probe, you would be in disbelief of the actual amperage drawn... :)

Disbelief in what way? More or less than my calculations do you think? I used this handy online power calculator from HP: http://h20000.www2.hp.com/bizsupport...ctID=c01510445

If you scroll down the 'HP ProLiant G5 and Earlier Servers' link.

I also have a KILL A WATT meter that shows me real time AMP usage but only had a chance to use it on group 3. Still have to test group 1 & 2 with it.

stickboy1375 08-13-2012 09:18 PM

Quote:

Originally Posted by Mellow (Post 987903)
Disbelief in what way? More or less than my calculations do you think? I used this handy online power calculator from HP: http://h20000.www2.hp.com/bizsupport...ctID=c01510445

If you scroll down the 'HP ProLiant G5 and Earlier Servers' link.

I also have a KILL A WATT meter that shows me real time AMP usage but only had a chance to use it on group 3. Still have to test group 1 & 2 with it.

Im going with way lower. but just for giggles, intstall the kill a watt meter and see what you are actually dealing with... You could install (3) 20 amp circuits, or (4) 15 amp circuits, both will give you the same amount of wattage, but may better balance the load out.


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