Discuss Current drawn from pc workstation in the Electrical Forum area at ElectriciansForums.net

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Tonkatoy27

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Hi guys,
I need to know the current drawn per pc workstation.
1x medium spec desktop pc
1x flat screen monitor

Simple enough you'd think.

I can't find my clamp meter. (my dads old meter, I never had call to use it, it's probably an antique) and I can't get a multimeter to work when connected in series with a 4 gang ext lead with said appliances plugged in.

Anybody know off hand?
The pc's say 5amps on the case and the monitors say 3amps 12v dc but there is no way they actually use that is there?

Thanks in advance.
 

telectrix

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connecting a multimeter in series to measure current is a dangerous practice on anything over 50V. find or borrow a clamp meter. i would imagine your load would be no more than a couple of amps total.
 
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Tonkatoy27

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Got one somewhere as I said, this is the first time I've ever needed it in 20 years and never used one in college. Sods law I can't find it.
I've got 37 workstations in an IT suite, I'm trying to work out if a 40 or 45amp supply on 10mm twin and earth going to be sufficient. (New IT suite but handily enough there is a redundant 10mm passing the suite. 35m run in basket.)
 

telectrix

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hope you're not thinking of putting 37 stations on 1 circuit .
 

Strima

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Most office type computers have on average a 500W PSU, round it up to 550W and you won't be far off the mark. With 37 stations there will also be a hell of a lot of earth leakage, will there be a server or any other items on the circuits?

I would look at possibly four 32A radials run in 4mm with high integrity earth.
 
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Tonkatoy27

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hope you're not thinking of putting 37 stations on 1 circuit .

LOL give me some credit tel, please.
Thinking along the lines of a submain to Crabtree cu in the room feeding 5 radial circuits with RCBO's. Max 8 pc's per RCBO to stop tripping, high integrity earth arangement.
Done all this plenty of times with no probs and if I was putting the sub main in from scratch it would be 16mm, on a 60amp mcb but as the 10mm was there anyway I wanted to work out the max demand and work backwards to see if a 40amp supply was big enough.
Cheers for the help all.
 
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Tonkatoy27

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Most office type computers have on average a 500W PSU, round it up to 550W and you won't be far off the mark. With 37 stations there will also be a hell of a lot of earth leakage, will there be a server or any other items on the circuits?

I would look at possibly four 32A radials run in 4mm with high integrity earth.
No additional equipment, Due to the design of the benches and RCBO requirements I've only got 8 pc's per circuits so was going to fit 16 or 20amp radials on 2.5mm radials with a 2.5 single as a HI Earth.
 
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Tonkatoy27

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Tonka with 8 tower pcs and 8 monitors you might be flying really close to that 10mA threshold. Do you think that the 2.5mm single earth would be advisable
Usually install 32amp rings so don't have to worry about a single forming the high integrity earth. How is a 1.5mm in the t&e plus a 2.5mm single different to 2x 1.5mm earths in a ring run in 2.5mm t&e?
 

malcolmsanford

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Reg 543.7.1.103 mate (iiii)

If you were using 2.5mm T + E in a ring final then you are then exceeding the 10mm total of all the conductors mate of the multi core cable so 2.5mm X 4 give you your 10mm and then your 2 X 1.5 gives you 3mm total of 13mm

As you say your doing a radial and if you exceed the 10mA, which you may not be but I think you'll be close, so is it worth taking a chance, then you need to radial it with a 4mm CPC if your are mechanically protecting it. There is nothing stopping you doing it on a 20amp radial using 2.5mm LIVE conductors, you just need to size the CPC as.
 
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Tonkatoy27

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So, back to my original question. Malcolm reckons less than 37amps and Strima thinks 81.5 amps. Hell of a difference in opinion. Christ, if it's 81 amps I don't think even 16mm will be man enough when I account for the grouping in the basket.
It looks like it's difficult to measure or know the correct load. What about trying the 10mm on a 45 or 50amp MCB?
 

Strima

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You need to work out what ratings the PSUs are and what they draw under average load. They could vary from a few watts at idle to 500 when running at full tilt. What happens in the future when they decide to upgrade, 1000W PSUs are pretty common although mainly used for gaming and 3D design etc.

Give it a clamp...

[video=youtube;qf8_tn7lBIc]http://www.youtube.com/watch?v=qf8_tn7lBIc[/video]

Sorry, couldn't help myself... :lol:
 

malcolmsanford

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Put it this way I'm sitting in my office here now .....we have 27 work stations, a couple of printers, a few switches and servers, 3 shredding machines and 3 HP all singing all dancing scanners ..................and it is merrily chugging away on a 40 amp MCB ........................

And there is a sub board of 4 circuits all with 16amp MCBs on it
 
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Tonkatoy27

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Put it this way I'm sitting in my office here now .....we have 27 work stations, a couple of printers, a few switches and servers, 3 shredding machines and 3 HP all singing all dancing scanners ..................and it is merrily chugging away on a 40 amp MCB ........................

And there is a sub board of 4 circuits all with 16amp MCBs on it
Yup, I'm inclined to have a stab at a 40 or 45amp mcb. If it doesn't hold then at worst we'll have to upgrade the existing 10mm and mcb. I'll give IT a shput and see if I can get them ti pin a max wattage on the psu's but I won't hold my breath...
 

Strima

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Just clamped my PC, 850W PSU pulling 160W when web browsing, thing is, what do you rate PC's at?
 
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Tonkatoy27

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I doubt the pc's will be working hard. I'm under the impression web browing is quite memory intensive and they can't access the web at the school. I would think that only one application at a time specific to the lesson would be used.
 

topquark

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Just clamped my PC, 850W PSU pulling 160W when web browsing, thing is, what do you rate PC's at?
Try clamping it during boot up Strima, you'll notice a much higher consumption then (if you have max on the clamp it'll be easier).
 

topquark

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I doubt the pc's will be working hard. I'm under the impression web browing is quite memory intensive and they can't access the web at the school. I would think that only one application at a time specific to the lesson would be used.
Most of the current draw is hard disk activity and adapter cards (graphics cards particularly, which is why a lot need additional cooling). Power consumption for modern processors is now down well below 50W even at full boost.
 
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