Branch circuit calculation for rack mount IT equipment

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orr263

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For calculating the size of a branch circuit for rack mounted IT equipment is it required to go by the nameplate rating of each piece of equipment?

An example would be if the namplates of servers , routers, monitors etc. add up to 25 amps but the actual running load is around 5 amps. Is it required to caculated the 25 amps as continuous current. Thanks.
 
Re: Branch circuit calculation for rack mount IT equipment

We always consider IT equipment as critical, special,important.U.P.S. backed ect.I would'nt skimp on amount of circuits.
Bob O. 84Pa.
 
Re: Branch circuit calculation for rack mount IT equipment

Will u mean only computers & servers rack mounted IT equipment

For computers ,in general 14" screen -150VA

16"screen -175VA,18" screen-200VA.Infact LCD display would consume less than 150VA .Server load would may differ because that is depend the no. of computers,we can take the name plate rating,also for any other electronic equipment .

Jeyakumar
 
Re: Branch circuit calculation for rack mount IT equipment

That's up to you. i've worked in a data center environment that sells 20 amp breakers to supply customers. some people run their circuits up to 19 - 20A thinking they're going to get "more for their money" if all of your equipment is running at full capacity at the same time you can trip your breaker, i've only seen it happen a handfull of times but each time the customer lost a lot of money. I couldn't tell you which way to go but most of the big name companies that i see tell them to let them know when they get to 10A normal running then buy more circuits. also, remember that you can send quite a bit of power to just one rack, but not a lot of cooling.
 
Re: Branch circuit calculation for rack mount IT equipment

Being that IT equipment is so dynamic and ever changing, I would recommend provide a minimum of (2) 20A branch circuits per rack. I always review the nameplate loads and provide more if necessary. The day after you wire the rack The IT guys may come in and swap the server with a larger model, or add modem or other peripheral devices, etc...
 
Re: Branch circuit calculation for rack mount IT equipment

It depends.
If you have tight control of what happens to the equipment in the rack, then you can use connected load.
If you don't have total control, then use nameplate rated loads.
It is not unheard of, in a 2N environment, if the HVAC can support it, to provide (2) 30 or 50A, 208V circuits to each rack. The new Blade type servers, can really use it up.
So it depends.
 
Re: Branch circuit calculation for rack mount IT equipment

Originally posted by ron:

It is not unheard of, in a 2N environment, if the HVAC can support it, to provide (2) 30 or 50A, 208V circuits to each rack. The new Blade type servers, can really use it up.
So it depends.
Click to expand...
ron did u meant HVAC & Server will be inter connected with single 208V circuit?

I never seen any server would be operated on dual mode 120/208V.

Moreover HVAC would draw power from RAW POWER panel where server is required UPS supply.we can not interconnect both.

I used to proposed 2 nos of 20A branch circuit for every rack,where one will be standby.

Jeyakumar
 
Re: Branch circuit calculation for rack mount IT equipment

Never connect the server and HVAC on the same branch circuit. Sometimes to save $$$, the rack mounted fans may use the same circuit with the servers.
 
Re: Branch circuit calculation for rack mount IT equipment

Orr263,
What kind of equipment are you going to be installing? what size racks do you use? We install mostly HP equipment and our most popular server is the DL380 top of the line. The load of any server is going to depend on how many processors and how many drives (raid 5 or mirrored) Anyway, for math purposes the average DL380 will draw 2 amps and a DL580 will draw 3 amps and lets don't forget the rack mount LCD monitor 1 amp. Doesn't that seem like a lot of work? We install 42U racks with rack mount power distribution. The specs on the rack mount PDU is 208V 24A so to make my life easy I give my racks a generic rating of 6kva. We have racks with 12 DL380's and some with two DL580's and eight DL380's, but are all the processors being pushed to the limit? I don't think so. We like redundancy here, so I run two 30 amp 208V single phase circuits to each 42U rack. Now as far as the blades go, I am usually installing four 30A 208V 3 phase circuits for them, and they are the server blades not the PC blades. Two from PDU "A" side and two from PDU "B" side much better then single phase. We also have S.A.N. racks with over 100 drives in them and at present I am running the two 30A 208V single phase circuits, but as we increase storage capacity and the speed of processors continue to increase this may all change. We will see. Hope this was some kind of help.

Kevin

[ January 17, 2006, 03:12 PM: Message edited by: kevinware ]
 
Re: Branch circuit calculation for rack mount IT equipment

Originally posted by kevinware:
Two from PDU "A" side and two from PDU "B" side much better then single phase.
Kevin
Click to expand...
The PDU is only a 3 phase unit with one input breaker, the "A" and "B" sides are usually just different breakers, after the main PDU input breaker. the phase distribution is usually by breakers on the "a" and "b" sides. for example, breakers 1 and 2 phase a, breakers 3 and 4 phase b, breakers 5 and 6 phase c, then back to 7 and 8 phase a. the reason i bring that up is it's much better to try to balance your load at the PDU level. if you currently are seeing high loading on the A phase adding breakers to the "B" side will not help balance your load, you need to count out the breaker positions to get the correct phase. also feeding "a" and "b" sides of a PDU will not give you redundancy.
 
Re: Branch circuit calculation for rack mount IT equipment

Dave,
I apologize for not being real clear on the our power distribution. Inside each rack we have two 208V distribution units with single 30 amp input. Four power strips attached to each of these units and mount inside the rack and these are what we plug our servers into. Now out on the floor we have four 150kVA PDU's. Two of these PDU's come from UPS-1, a 500kVA UPS from powerware and the other two come from UPS-2 a 500kVA unit also. We do only have one back-up generator, just a small 1.5MW unit :D

Our general setup would be one 208V 30A circuit from PDU on UPS-1 and one 208V 30A circuit from PDU on UPS-2. The blade setup will be a little different, their distribution units have two inputs. So one 30A 208V from each PDU.
Edit to add the above.

[ January 17, 2006, 04:01 PM: Message edited by: kevinware ]
 
Re: Branch circuit calculation for rack mount IT equipment

aaah gotcha, sounds like a pretty nice set up. i just wanted to make sure nobody made the mistake of thinking that one PDU's a and b sides would give redundancy, the way you have it set up is definitely the way to go.
 
Re: Branch circuit calculation for rack mount IT equipment

Dear dave_asdf & kevinware ,

i am basically electricl oriented,cuold you clarify the follows,

1)raid 5 or mirrored

2)42U racks

3)server blades not the PC blades

4)S.A.N. racks with over 100 drives

Please...

5)
 
Re: Branch circuit calculation for rack mount IT equipment

Originally posted by kevinware:
Dave,
Inside each rack we have two 208V distribution units with single 30 amp input .
Click to expand...
.

Did you mean one 30A single phase or 2 Nos of (30A each)single phase.?
 
Re: Branch circuit calculation for rack mount IT equipment

well Jeyakumar, i am also mostly electrically oriented so i can't make any good recommendations on the IT equipment you are talking about other than when selecting a 42u (server rack brand name) you should look at security, space and cooling. i don't know much about the different data storage/sharing methods unfortunately, sorry.
 
Re: Branch circuit calculation for rack mount IT equipment

Originally posted by orr263:
For calculating the size of a branch circuit for rack mounted IT equipment is it required to go by the nameplate rating of each piece of equipment?
Click to expand...
645.5(A) of the 2005 NEC says that the branch circuit conductors supplying data processing equipment shall have an ampacity not less than 125% of the total connected load.
 
Re: Branch circuit calculation for rack mount IT equipment

Kalanjeta,

1.) Raid 5
Block Interleaved Distributed Parity: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID.

That is a real fancy definition isn't it :D
Now, what that means to me is this. In a raid 5 setup I have 6 hard drives, 5 active and one on-line spare. The system sees the 5 drives as one big drive and my data is spread out (striped) on all five drives as 1's and 0's. The good things about this setup is if I have one drive go bad, the system is smart enough to figure out which 1's and 0's is missing and start rebuilding them to the on-line spare drive.

2.)Mirrored setup:
A technique in which data is written to two duplicate disks simultaneously. This way if one of the disk drives fails, the system can instantly switch to the other disk without any loss of data or service. Disk mirroring is used commonly in on-line database systems where it's critical that the data be accessible at all times.

Another fancy definition. We use 3 disk for this setup. Two as our online disk and one for a spare. Again if I lose one active drive my spare kicks in and I am still online. Not as reliable as raid 5. The power consumption will be less though because of the less number of drives.

2.) 42U rack:
This mean nothing more then the height of the rack itself. Hp Racks

3.) Server blades:
These guys are nothing more then a server in a smaller package. In a rack space of 20U I can get 10 DL380 servers (2U of space for each DL380). In that same 20U space I can get 3 server blade cages and in each cage I can get 8 server blades, which means 24 servers. For better information check out HP's web site.

4.) S.A.N. (Storage Area Network)
We have a large rack out on the floor that does nothing but act as a data storage area. This setup is like this:

12 cages in the rack
each cage can have 14 drives, I think we have 10 146.8 GB drives per cage right now. So if you do the math that is 17.616 Tera bytes of storage space, that is a lot of damn space.

5.)The setup inside of our racks:
Check out this pdf.
Rack setup

So for a standard rack I would install two 208V 30A circuits. One circuit coming from UPS-1, and one circuit coming from UPS-2.

For a Blade rack I would install 4 208V 30A 3-phase circuits. "Scotty, I need more power" :D

Well, I sure hope all this means something to you Kalanjeya, but my opinion I would rather be in your shoes, a "EE"

Thanks,
Kevin
 
Re: Branch circuit calculation for rack mount IT equipment

Thanks kevinware & dave_asdf .

your data would help me a lot when i do IT related design work.

Thanks again

Jeyakumar
 
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