Computers on a circuit

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How many computers can you put onto one circuit. I have heard that if you put too many, it can start acting funny. I normally don't put more than 2 on a circuit. Also do I need to install some power correction or anything to the panel/circuits to correct the "noise" problem?

I am designing a 911 call center and a sheriff's station. The 911 center will have 10 computers and monitors. Should I bring an Isolated ground back to the panel? I toured another 911 center and they had isolated ground receptacles.
 

Mr. Bill

Senior Member
Location
Michigan
I usually aim for a maximum of 2 computers or workstations on a circuit. I've had as many as 6-8 computers on a single circuit with no noticable problems. They had flat panel monitors which use less power. And it was an after the fact design change done to avoid cutting a brand new floor.

I would suggest a dedicated neutral conductor but I have not heard of a dedicated ground. Could this be a 911 standard for reliability? You might want to specify a TVSS connected to the breaker panel.

I don't think 10 computers would cause a significant noise problem that would require correction. It can get expensive to try to reduce harmonics at the panel. A zig-zag transformer can reduce alot of harmonics upstream from the panel. But those cost about twice the normal price for a transformer.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I would also go with 2 workstations per circuit. That of course assumes that any printers are on separate circuits. For example, if each workstation had its own printer, I would use one circuit per one workstation.

I didn't think anyone used isolated grounds for computer stuff anymore. I am in the middle of a design for an office remodel, and we are removing the isolated ground bar (and related conductors) from all the panels.
 
Hmm, usual datacenter practice is to put 13-15a worth of computers on a 20a circuit- that could be two or that could be 8-9. For desktop systems in a dispatching environment, if $$ permit, give each workstation a separate circuit.

Is the entire dispatch system going to be on a single UPS or will there be individual UPSs per station or computer?

Isolated grounds? Nobody bothers for computer installations*. I would consider dedicated neutrals, not for harmonics but for reliability.

*I have seen a few (orange) outlets installed in the last ten years, but looked like a way to identify the UPS-protected outlets from the unprotected outlets. I didn't actually check to see if they were really iso ground circuits.
 

Michael15956

Senior Member
Location
NE Ohio
Cliff,

The Copper Development Association has printed materials and recommendations for power quality issues related to what you are planning. They can be reached at 888-480-4276.

There is no mention of isolated grounds but they do recommend uses of separate insulated copper wire as grounding conductors.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Hum something is wrong here. You are designing a 911 center and none of the critical equipment is being supplied from a dedicated dual conversion UPS and a generator ahead of that? That will go over like a you know what in the punch bowl when a thunderstorm tears up the town and the dispatchers are outside sending smoke signals up for communications.
 
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We are planning on putting in a generator to back up the 911 and a detention facility. I was planning on putting some kind of UPS on the panel (s) dedicated for the critical operations. So they should not lose power.

About the orange circuits, I could see someone putting in a different color plug to show that that is a "UPS" plug. The facility that I toured had a generator with a UPS system with 5 or 6 panels that were backed up.

I have had contractors tell me that when you have a bunch of computers in the building, then you will start to have noise problems. I guess my question is, Is there actually a problem or is it more of a myth?

Thanks for all your help.
 

dbuckley

Senior Member
Noise problems.... hmmm...

If on a three phase system a significant proportion of your loads are non-linear (like computers, HF fluorescents etc) then you will have high neutral currents. If the majority of the load is linear loads like motors without VSDs, magnetic ballasted fluorescents, incandescent lighting or resistance heat then you wont notice the harmonic current contribution.

So for most mixed load installations, its a non-issue.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Myth. I design data centers and telephone offices. We don't use IGR period for anything. A dual conversion UPs is the best system known to man to eliminate any noise problems, so it is not an issue.

IGR was antiquted years ago when communication I/O devices use ground as a reference or signal path (RS-232, coax, etc). All that is long gone with ethernet,optical, and other forms of balanced forms of signal transmission.
 

robbietan

Senior Member
Location
Antipolo City
I have 7 computers on a circuit and no problem. What I did was put an isolation transformer for each computer, since we dont use neutral wires here.

what we advise is to put all computers in one circuit, laser printers in another, airconditioning units in another. and all is happy.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Cliff Brady said:
About the orange circuits, I could see someone putting in a different color plug to show that that is a "UPS" plug.

Just use a white device with a red plate.
 

spsnyder

Senior Member
I'm working on a retro-fit for a 911 call center now. Nearly all power has UPS power from a Generator/Normal Source. Surrounding offices have a mixture of Generator and Normal Power. The project involves adding a UPS recept. to all the offices. They want the computers to operate seamless. The Gen. recept. loose power for a few secs. I would recommend sizing the UPS Conservatively and adding UPS power in the offices as well.

As far as colors go, they used white - Normal; Red - Generator only; Orange - UPS/Generator. Although they inexplicably did not adhear strictly to the color scheme which has caused a fair amount of problems as you can imagine. Best of luck.

Regards,
 

bsh

Senior Member
If you only put 2 computers on a circuit it will allow for the small heater that the operator uses in the winter.
 

RayS

Senior Member
Location
Cincinnati
Cliff Brady said:
I have had contractors tell me that when you have a bunch of computers in the building, then you will start to have noise problems. I guess my question is, Is there actually a problem or is it more of a myth?

one time only did I see computer loads create a problem, and that was neutral heating, presumably from harmonics. Building was a warehouse, converted to a data center, and some of the neutrals actually had melted insulation.

I'd lean towards dedicated runs for each workstation, just so failures/maintenance only take down one.
 

e57

Senior Member
bsh said:
If you only put 2 computers on a circuit it will allow for the small heater that the operator uses in the winter.

Back when I did a lot of service work I would get those calls about office circuit breakers tripping. So often that it was the first question I asked, "how many space heaters are on the circuit?" Most of the time it was 'toe warmers', a little space 800w heater under the desk. One woman would get one, then all of her neighbors too.... POP! Sometimes full on 2000w ones! One a few occasions it was hard to convince woman office managers that this was the problem - because they had one too. Had to show them the amp clamp... One that I went to, a male office manager who was having a revolt on his hands about the level of air conditioning had me help him relocate several women so they could keep the heaters...
 

cadpoint

Senior Member
Location
Durham, NC
pondering

pondering

Well, I'm just wondering what consideration for Spec'n prefab low wall partations and their listed wires ? :roll:
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I'm having a similar issue right now. In a restaurant I wired last year, they're having problems with the POS system losing terminals. The POS vendor told the restaurant owner that the electrical system is horribly improperly wired. :mad:

Now, following the vendor's guidelines, I had installed a dedicated circuit for the system, with MC cabling and IG receptacles and methods. (I know, but that's what they wanted.) The terminals, printers, and the server have APC UPS's. :smile:

In the past three weeks in particular, they have had required several visits to replace equipment and/or re-program the system. Of course, I just got the first call about this today, so I managed to fit in an unplanned visit to investigate. :cool:

What did I find? :confused:

Where one of the printers used to be plugged in, in the orange receptacle, I found instead the plugs of a small, under-counter refrigerator and a coffee maker. :rolleyes:

I told them to call me back after they relocate the appliances.
 

cadpoint

Senior Member
Location
Durham, NC
Makes you wonder

Makes you wonder

Exactly Larry, I've seen exactly that, hords of stuff on the one maybe two receptacles ... 1st offense -power Strip bar than Fans/ Heaters, Cellphone charger(granted marginal) etc., etc, etc,. One just can't engineer that.... ((and I held off posting your basic statement))
 
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e57

Senior Member
Oh Larry restaurants are a subject on to themselves... And so would POS dealers for that matter.

  • POS dealers - the problem is always 'electrical' no matter how its wired. Not the software, or their equipment.
  • Restaurant owners - "So I can't plug a panini grill, a coffee maker, a microwave , and the POS printer into those four outlets?" (For the fifth and final time - NO!) "I'll go get my label maker..."
When I do a restaurant, I usually get the owner/manager to bring in the cooks and find out what they are really going to do in the kitchen. "Tell me now - because in the middle of the lunch rush you don't want to be running for the circuit breaker." Something they have all done before. Half the time I find out about equipment that wasn't on the plans at all.
 
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