Recommendations for 100+ computer environment

[andyf]

I'm not an electrician and I'm looking for guidance.

Where would I find recommended electrical specifications for supplying multiple
computers in a non-data center, non-critical environment? (Specifically,
computer labs for student use.)

I typically have about 100-150 computers connected to a single
distribution panel (about 25 computers per classroom). I try to keep at
most 4 computers per 20Amp circuit.

My question has to do with neutral bus capacities and whether or not
isolated-ground circuits are suggested.


At one time, I was told that computers need IG circuits. I then learned
that 200% neutral bus capacities are more important because of the
harmonics that computers put on the electrical system. I don't know where the 200% neutral applies though.

At this point, I don't know what to request.

(I will forever have the memory of the president's computer freezing up
because the electrical circuit his computer used was connected to the
same distribution panel as a circuit where someone was using a jack
hammer.)

The typical configuration appears to be:
bldg feed->main panel->distribution panel->outlet

I'm sure there's information you need that I didn't provide. Let me know.

Thanks for any information you can provide.
Andy Farrior
IT Director
Victoria College

 

[petersonra]

Re: Recommendations for 100+ computer environment

You seem to be on the right track. Isolated ground (somewhat of a misnomer) is probably not really needed, as it really does not do much for you.

With the small loads you have on the 20A circuits your neutrals are quite adequate, although the engineer reviewing the electrical drawings may wish to ensure the feeder conductor neutral is adequately sized.

Biggest thing is making sure you have an adequate number of outlets in the area. Its amazing how many can get used up, and power strips are a poor choice as a substitute for putting in enough outlets in the first place.

 

[charlie b]

Re: Recommendations for 100+ computer environment

Your notion of 4 computers per 20 amp circuit is a good limit. Also, your description of ?the typical configuration? is correct (bldg feed->main panel->distribution panel->outlet). If any part of this configuration gets a 200% neutral, it would be the ?feeder? between the main panel and the distribution panel.

But is this a new project that is in its early planning stages, or an existing facility that is experiencing problems? If it is not yet built, then there are additional options for dealing with harmonics. Your design engineer or electrical contractor can give you suggestions. If it is built, and if you are experiencing problems, then it would be hard for me to help without first knowing much more about the existing configuration and the nature of the problems.

 

[charlie tuna]

Re: Recommendations for 100+ computer environment

your on the right track --- biggest issue is not using common neutrals. or provide dedicated circuits to each group of four computers. isolated ground is not necessary but a regular ground conductor should be included in the installation. individual neutrals for each circuit is very important. the panel providing computer power should have a ground bus installed and connected to the building's ground system via the feeder raceways sized per code. i would recommend a copper bus panelboard over a loadcenter panel to provide computer power and the feeders should be properly sized for the total computer load with full sized neutral conductor. many installations where panels feed only computers will also have some type of surge suppresor also??

 

[andyf]

Re: Recommendations for 100+ computer environment

petersonra - "Biggest thing is making sure you have an adequate number of outlets in the area. Its amazing how many can get used up, and power strips are a poor choice as a substitute for putting in enough outlets in the first place."

I prefer not use power strips, however, I ran into a problem with the engineers when I wanted to increase the outlet count on a circuit. Evidently, there's a limit to the number of outlets allowed on a given circuit regardless of the anticipated load.

Typical computer system:
computer - 3A
monitor - 1A
speakers - 800mA (wall-wart AC/DC transformer)


ratings based on UL tag on unit.


charlie b - "an existing facility that is experiencing problems?"

It's an existing facility, but it's under remodel; so, some of the electrical can be redone.

The problems I've had in the past include:
- computers freezing/rebooting/monitor display problems when a floor waxing machine is used.
- Damaged power supplies in ceiling mounted LCD projectors. In one case, the best we could tell, the projector was the only device on the circuit. Unfortunatly we went through three devices before we looked at electrical being the problem. (first brand had a history of failure, second, different brand, was dismissed as bad unit. third, hmmm must be electrical problem)


Let's see if I have a starting point:
1 - Individual neutral per circuit going back to the distribution panel.
2 - 200% neutral on the feeder line between the main panel and the distribution panel.


If there are general-use outlets on different circuits connected to the same distribution panel as the computer circuits, is there a problem with using heavy machinery on the general use outlets (e.g. floor waxers, large drills for making 3" holes in concrete...)?


Thanks!
Andy

[ February 03, 2005, 02:42 PM: Message edited by: andyf ]

 

[charlie tuna]

Re: Recommendations for 100+ computer environment

the ideal situation would be to bring in a new feeder for computer power. the existing circuits in the area be used for copiers---printers ---floor cleaning machines or general use outlets.

your original problems were probibly the result of common neutrals which allows other circuit loads to change the voltage seen by the other circuits that are common to the neutral.

a few months ago a law firm was having problems with their main server rack --- some programs linked to their offices in new york would stop and re-boot themselves ---three to four times per hour. these programs were loosing data from the problem. tracing the circuit we found the server had a common neutral with a copy machine in the mail room! we recommended a dedicated circuit which was installed by the building's electrical contractor. he had moved the copy machine to access the area and plugged it in another receptacle.

the I.T. person never shutdown the server and transfered the plug to the dedicated circuit. last week someone moved the copier back to it's original outlet and the problem re-appeared! they called us back out and when we traced the circuit we found the problem. the electrician couldn't shutdown the law firm's server during operating hours--they had to do that --- but never did!

 

[bonding jumper]

Re: Recommendations for 100+ computer environment

Isolated grounds are required for predominantly highly sensitive "New) servers and telecom equipment. For computer loads that are not critical, ie. student computer lab there is no need for isolated grounds. Isolated grounds are misleading and overrated. I deal with a lot of financial clients who have to adhere to sec regulations for power and we typically don't like to specify isolated ground circuits for a couple reasons.

One is that typical computers do not react any different on a isolated or non isolated ground.

Two, installation. It is very easy for a contractor, durring the installation of 300+ outlets, to mistake the isolated ground from the equipment ground. If this happens once your complete isolated grounding system loses all integrity and becomes a secondary equipment ground. Or if one isolated grounding wire gets nicked durring installation/pulling the same occurs, system is lost. If a janitor comes to replace one outlet that a teacher has been complaining about, and see's the two grounds in the junction box, and decides to terminate them together on the new outlet, the system is no longer isolated.

Three is the expense/reward that is achieved. Running one additional #10 wire to all computer equipment can be costly and the money may be better spent into branch circuit monitoring or another upgrade on the system.

200% rated neutrals are very important for computer loads. They should also be combined with k-13 rated transformers instead of regular to deal with the non linear loads.

[ February 07, 2005, 02:30 PM: Message edited by: bonding jumper ]

 

[pierre]

Re: Recommendations for 100+ computer environment

I am surprised no one mentioned TVSS protection.
I would have your electrician or a manufacturer design some protection that will include (at the least)Feeder panel protection and point of protection at each receptacle.
Redundant protection is the minimum these days.

 

[ron]

Re: Recommendations for 100+ computer environment

To make installation easier, do you need any of the leniencies provided by Article 645? Since you are not in a critical environment, the reliability reduction required in 645.2, to use 645, might be worth it to reduce install cost or modification.

 

[don_resqcapt19]

Re: Recommendations for 100+ computer environment

bonding jumper,

Isolated grounds are required for predominantly highly sensitive "New) servers and telecom equipment.

There is no evidence that isolated grounds are needed or effective.
Don

 

[petersonra]

Re: Recommendations for 100+ computer environment

Originally posted by don_resqcapt19:
bonding jumper,

Isolated grounds are required for predominantly highly sensitive "New) servers and telecom equipment.

There is no evidence that isolated grounds are needed or effective.
Don

In fact some time ago I read an interesting article about the use of isolated grounds. It seemed to indicate that in many cases they were actually counterproductive. I wish I had kept a copy.

The author seemed to be of the opinion that having a good local ground plane (like the floor of your computer room) properly bonded to the building electrical service was far more important.

 

[bonding jumper]

Re: Recommendations for 100+ computer environment

Originally posted by don_resqcapt19:
bonding jumper,

Isolated grounds are required for predominantly highly sensitive "New) servers and telecom equipment.

There is no evidence that isolated grounds are needed or effective.
Don

Well, you can say that, but some manufacturers require them. If you don't install them, you void the warranty.