Office Workstation Calculations

[mahaney03]

Hello all,

I've been going back and forth in my mind trying to determine what would be the best way to design the loads for an office space. I see per NEC 220.14 (A) I should be using the nameplate data for the items that are planned to be installed in a certain area. When I come to the loads of the equipment, I see things like the Dell Monitor rated for 2.5 A max but listed as a power consumption of 135 watts. To me, it's more realistic to be using the average power consumption but ever since reading that code, I feel I'm responsible for properly designing the load to handle what's rated based on what the workstation can handle.

This is my typical workstation load currently all in 120V:

(2) Monitors - 2A
(2) CPUs - 3A
(1) big CPUs - 10.83A

All of it is obviously never going to run at a full load but if it trips, it would still be my responsibility I feel. Is there a general diversity factor I should be taking for computer loads or do I always need to make sure the circuit can handle the listed nameplate data? I'm looking for some insight and experience since I'm still young and would like some other perspectives on the matter.

Thanks for your time,

Mike

 

[jumper]

Listed nameplate value.

Use kVA not kW if available.

No load diversity factor for this type of calc.

 

[mahaney03]

Listed nameplate value.

Use kVA not kW if available.

No load diversity factor for this type of calc.

Thank you Jumper.

 

[gar]

180129-2233 EST

Measurements on several of my items at 123 V.

1.2 A 98 W ---- 20" CRT over 20 years old
0.4 A 28 W ---- 20" LCD possibly 10 years old
0.9 A 70 W ---- XP Desktop 15 years old
0.3 A 15 W ---- Low cost Lenovo Desktop about 2 years old

.

 

[steve66]

Listed nameplate value.

Use kVA not kW if available.

No load diversity factor for this type of calc.

I don't quite agree that we have to use the full kva rating with no diversity factor for general computer equipment. If a receptacle is for a specific load, we have to use that load for the calc, and you are correct, there is no diversity factor for that type of load.

However, computers won't draw their full rating. The real load will be much less, and Gar's numbers support that. And we won't really know exactly what computer will be plugged in where. People and their computers will move around in the office, computers will have equipment and monitors and printers added and removed. And they will be replaced and upgraded, and so on and so on.

I would count the big computer at 10 amps. I'd probably even give it a dedicated circuit. But I don't see any point in trying to actually count the VA's of each piece of small computer equipment. To be sure, you don't want breakers tripping, but I've never had any problem just using general rules of thumb.

I generally just put X number of cubicles on a circuit, or X number of small private offices on a circuit. Or I think one could use the 1 VA/SF number from the code and add some kind of safety factor.

 

[jumper]

I don't quite agree that we have to use the full kva rating with no diversity factor for general computer equipment. If a receptacle is for a specific load, we have to use that load for the calc, and you are correct, there is no diversity factor for that type of load.

However, computers won't draw their full rating. The real load will be much less, and Gar's numbers support that. And we won't really know exactly what computer will be plugged in where. People and their computers will move around in the office, computers will have equipment and monitors and printers added and removed. And they will be replaced and upgraded, and so on and so on.

I would count the big computer at 10 amps. I'd probably even give it a dedicated circuit. But I don't see any point in trying to actually count the VA's of each piece of small computer equipment. To be sure, you don't want breakers tripping, but I've never had any problem just using general rules of thumb.

I generally just put X number of cubicles on a circuit, or X number of small private offices on a circuit. Or I think one could use the 1 VA/SF number from the code and add some kind of safety factor.

I am not a train driver (engineer), I can only do what 220.14 tells me to do.

 

[mahaney03]

I don't quite agree that we have to use the full kva rating with no diversity factor for general computer equipment. If a receptacle is for a specific load, we have to use that load for the calc, and you are correct, there is no diversity factor for that type of load.

However, computers won't draw their full rating. The real load will be much less, and Gar's numbers support that. And we won't really know exactly what computer will be plugged in where. People and their computers will move around in the office, computers will have equipment and monitors and printers added and removed. And they will be replaced and upgraded, and so on and so on.

I would count the big computer at 10 amps. I'd probably even give it a dedicated circuit. But I don't see any point in trying to actually count the VA's of each piece of small computer equipment. To be sure, you don't want breakers tripping, but I've never had any problem just using general rules of thumb.

I generally just put X number of cubicles on a circuit, or X number of small private offices on a circuit. Or I think one could use the 1 VA/SF number from the code and add some kind of safety factor.

Normally I would feel fine with putting up to 3 workstations on a circuit when the load was 2-30" monitors and 2 CPU's. When the client decided to add 5 more cpus to most existing workstations and a few super computers, then things get a bit unclear. I want to always do my best to get things right but the more and more I progress in this industry, it seems that there are many areas that need to be defined more.

I know as engineers we should be thinking outside of the box but at some point, couldn't that be thrown back at us for not properly following the code and going based of what was guesstimated?

 

[jumper]

I know as engineers we should be thinking outside of the box but at some point, couldn't that be thrown back at us for not properly following the code and going based of what was guesstimated?

You stamp it, you own it.

 

[RumRunner]

You stamp it, you own it.

Don't let that get in your head. With the computer technology making strides in keeping up with the times, computers now are super energy efficient compared to those 40 years ago or even ten years ago.
Electronics as applied to computers make advances every 18 months which in most cases leaves those dated NEC guidelines get obsolete.
Unlike those IBM mainframes that ran on vacuum tubes. . . one mainframe with super efficient microprocessors run 70 percent less energy.
Perhaps NEC needs to review their position on this.

 

[jumper]

Don't let that get in your head. With the computer technology making strides in keeping up with the times, computers now are super energy efficient compared to those 40 years ago or even ten years ago.
Electronics as applied to computers make advances every 18 months which in most cases leaves those dated NEC guidelines get obsolete.
Unlike those IBM mainframes that ran on vacuum tubes. . . one mainframe with super efficient microprocessors run 70 percent less energy.
Perhaps NEC needs to review their position on this.

And how does this apply to me as an installer following a EE stamped set of drawings/specs?

Unless I willing and knowingly install something that is dangerous or against code, the onus is on the EE.

EEs get great allowance on what is acceptable, like annex B-which is forbidden to me, but they bear the responsibility for this power.

 

[RumRunner]

And how does this apply to me as an installer following a EE stamped set of drawings/specs?

Unless I willing and knowingly install something that is dangerous or against code, the onus is on the EE.

EEs get great allowance on what is acceptable, like annex B-which is forbidden to me, but they bear the responsibility for this power.

Saving money is also a part of good engineering practice. Would you run #12 wire if you can safely do with #14. Being caught up with the doctrine that NEC xxx tells you when in common sense you can do differently, safely and economically is beyond the pale.

 

[jumper]

Saving money is also a part of good engineering practice. Would you run #12 wire if you can safely do with #14. Being caught up with the doctrine that NEC xxx tells you when in common sense you can do differently, safely and economically is beyond the pale.

If the NEC mandated or a EE stamped set of drawings said to run 250 kcmil CU conductors for a 5A load, I would be at the supply house picking up 3” conduit. No hesitation what so ever.

 

[mahaney03]

And I feel the same way. Rules are rules and if they can still pin the fault on us for not following proper procedure, why put myself at risk?

 

[mayanees]

minimum essential

minimum essential

Hello all,

I've been going back and forth in my mind trying to determine what would be the best way to design the loads for an office space. I see per NEC 220.14 (A) I should be using the nameplate data for the items that are planned to be installed in a certain area. When I come to the loads of the equipment, I see things like the Dell Monitor rated for 2.5 A max but listed as a power consumption of 135 watts. To me, it's more realistic to be using the average power consumption but ever since reading that code, I feel I'm responsible for properly designing the load to handle what's rated based on what the workstation can handle.

This is my typical workstation load currently all in 120V:

(2) Monitors - 2A
(2) CPUs - 3A
(1) big CPUs - 10.83A

All of it is obviously never going to run at a full load but if it trips, it would still be my responsibility I feel. Is there a general diversity factor I should be taking for computer loads or do I always need to make sure the circuit can handle the listed nameplate data? I'm looking for some insight and experience since I'm still young and would like some other perspectives on the matter.

Thanks for your time,

Mike

DuPont instilled in me the concept of minimum essential design. Meet your client or customer's requirements with an NEC-compliant design and define the capacity, i.e the amount of equipment your design covers. Anything beyond that is at their request.

 

[mahaney03]

DuPont instilled in me the concept of minimum essential design. Meet your client or customer's requirements with an NEC-compliant design and define the capacity, i.e the amount of equipment your design covers. Anything beyond that is at their request.

Could you elaborate more? Are you saying to state something like each workstation is designed to take 500 VA up to a max of 3 workstations on the same circuit?

Is there any code that you could refer me to in order to justify this?

 

[augie47]

In practice I have found a "real-life" variable.... what is the end customers position on unit heaters at work stations !!
If Betty-Lou is allowed to have her foot warmer she can require more than 5 monitors.................

 

[mayanees]

Could you elaborate more? Are you saying to state something like each workstation is designed to take 500 VA up to a max of 3 workstations on the same circuit?

Is there any code that you could refer me to in order to justify this?

You've been given a specific scope to meet with your design. I'm suggesting you state the maximum allowable # of workstations using your design, as you stated: (3) at 500VA and qualify your references, ie. NEC, Computer Standard XYZ, etc.
Or state: this allows for XX% growth due to client's planned buildout.

 

[steve66]

In practice I have found a "real-life" variable.... what is the end customers position on unit heaters at work stations !!
If Betty-Lou is allowed to have her foot warmer she can require more than 5 monitors.................

I attended a lighting seminar where they said space heaters were the largest office equipment load on average. They took more power that the lights, and more than the computers, or any other single item.

Then it was explained that this is largely due to dress code double standards between men and women. The fancier and more upscale the office, the more it was expected that men would wear heavy suits, and the more it was expected that women would wear shorter, more revealing dresses.. And the thermostat is always set so the men comfortable.

So the overall point was "Don't blame the women. Blame the double standard dress code and whoever gets to decide where the thermostat is set."

 

[retirede]

I attended a lighting seminar where they said space heaters were the largest office equipment load on average. They took more power that the lights, and more than the computers, or any other single item.

Then it was explained that this is largely due to dress code double standards between men and women. The fancier and more upscale the office, the more it was expected that men would wear heavy suits, and the more it was expected that women would wear shorter, more revealing dresses.. And the thermostat is always set so the men comfortable.

So the overall point was "Don't blame the women. Blame the double standard dress code and whoever gets to decide where the thermostat is set."

Where I worked, the women wore jeans and sweaters & still required space heaters. We guys pretty much wore short sleeved shirts.

 

[jumper]

So the overall point was "Don't blame the women. Blame the double standard dress code and whoever gets to decide where the thermostat is set."

Nah, my standard modus operandi is blame everything, no matter what, on the first train driver I can think of.

I never bother with details like if the poor engineer was even involved.:angel: