computer loads?

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steveng

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i am providing 1 20volt receptacle circuits for 20 computers.


when calculating the load requirements for computers? should i use

1. 3 computers per 20 amp circuit, sharing neutral?
each computer rated at 3.5 amp.
 
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steveng said:
i am providing 120volt receptacle circuits for 20 computers.


when calculating the load requirements for computers.

1. 3 computers per 20 amp circuit, sharing neutral?
each computer rated at 3.5 amp.
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those are all statements.
 
Is it a three phase system? If so, harmonics can be induced onto the nuetrals. This is caused by the non-linear computer power supplies.

Shared nuetrals would be a bad idea in this case.

I think mwbc on a single phase system would be O.K.

I'm sure someone sharper than I will post what type of three phase system has the harmonics problem.

It's too late to whip out the Mike Holt Journeyman Exam book which explains this topic in detail.
 
I haved looked through my reference books and can't find anything.

I know triplen harmonics from non-linear loads can overheat shared nuetrals on certain three-phase systems.

I can't find what type of system is susseptable to this problem.
 
I know triplen harmonics from non-linear loads can overheat shared nuetrals on certain three-phase systems.
I can't find what type of system is susseptable to this problem.
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The potential of an overloaded neutral is only a problem with 3 phase wye systems.
Don
 
computer circuits

computer circuits

I just finished a computer lab/ classroom at a university. The classroom has 24 pc's. The plans called for 6- 20 amp circuits with 6 neutrals. I use to think a computer pulled about 1.5 amps. But now I guess it is around 3.5 amps?????
 
Hi guys. River Boy I am. This is my first post. Shared neutrals on computers with their switching power supplies ain't good. Switching power supplies=non linear loads. The day is coming when we'll have to up-size feeder and service neutrals on wye systems to compensate for this.
 
Hi

I've designed a UPS for a computer room.

I have sized my neutral rated 200% and my panelboard as well. There is 111amp on each phases. So the neutral cable must be sized for at least 111*square(3) = 195A.
 
steveng said:
i am providing 1 20volt receptacle circuits for 20 computers.


when calculating the load requirements for computers? should i use

1. 3 computers per 20 amp circuit, sharing neutral?
each computer rated at 3.5 amp.
Click to expand...
I guess one could spend all sorts of resources on this, but generally speaking if they're standard work stations, I'll apply 500VA per station and get on w/ it. I tend to share (1) circuit w/ no more than (3) work stations as you've stated. Sometimes you'll need to pick up something else or end up w/ (1) station getting a dedicated circuit - it is what it is. I've never had any issue w/ the above method/philosophy.
 
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I'm curious. Has anyone here put an amp meter on a three phase shared neutral system, with 3 computers on each circuit, to see what the actual load on the neutral was?
 
No, but in an example from an APC white paper: the neutral sizing current requirement as % of phase conductor:

Networking equipment only (4 different servers, a tape library, and a Network Attached Storage System) - 8 %

All PC workstations - 102%

50/50 mix of PC's and network equipment - 42%

Another Data Center case study was 20%.

Neutral size 2 gauges larger in a call center, anything else, same size as phase conductors.
 
computer load is a factor of the power supply which ranges from 250 watts to 600 or so. No need to overbuild your circuits if the systems are just small workstations with no real need for big graphics cards, which seem to be the main power hogs.
 
danickstr said:
computer load is a factor of the power supply which ranges from 250 watts to 600 or so. No need to overbuild your circuits if the systems are just small workstations with no real need for big graphics cards, which seem to be the main power hogs.
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True, but then you'll find someone's stacked 5-10 PCs in a single cube. Or there's a small refer, or a laser printer, etc. I'd much rather have spare capacity than save panel space. And =iIn some areas, like Silicon Valley, offices are often rented with existing cube furniture, so planning on a small load doesn't do any favors for future renters.
 
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