Office Workstation Calculations

[junkhound]

Good comments on 'Betty-Lou" and space heaters.

Here is an example and case history indicating a 'beyond code' factor that train drivers should consider.

The EU controls what PF and harmonics a load can be, so most electronics being sold in Europe have PFC circuits. Neither the code or USA laws govern PF or harmonics. May have missed some regulations in the last ten years though as have not bothered to keep up being mostly retired old fart?

Anyway, this case history was in early 1990s when entire office buildings first saw computer installations. Indicates the train driver should have put a scope on one of the new computers and looked at the waveform.

Building supplied by a delta-wye transformer on the rooftop. Nearly a thousand new computers and CRT monitors distributed to workers in February.

If train driver had looked at input current waveform, she (notice I assumed it could have been a female :happysad would have noticed the current spikes indicating the computers had simple diode bridges for the CPU power supplies.

Existing cubicles took into account a percentage of "Betty-Lou" heaters, etc. in offices/cubicles. IIRC every office had it's own 20 A breaker an one 20A circuit for each 4 cubicles.


So, summer time comes around and the delta-wye transformer on the roof burns up on the first hot day.

Why? Obvious to those skilled in the art but maybe not to those who simply 'follow the code', the 3rd and 9th harmonics produced by the diode bridges in all the computers ran around in a circle in the delta overheating it. Nothing to do with overall kVA, simply that harmonics of the massive non-linear loads and resultant harmonics.

Kapow.

 

[pv_n00b]

This seems to be treating the branch circuit calc like a workstation is a load on a dedicated receptacle. I would think that if receptacles are installed in work areas they will have workstations and other equipment plugged into them. So shouldn't the receptacle calcs in 220.14(I) and (K) be used?

 

[jumper]

This seems to be treating the branch circuit calc like a workstation is a load on a dedicated receptacle. I would think that if receptacles are installed in work areas they will have workstations and other equipment plugged into them. So shouldn't the receptacle calcs in 220.14(I) and (K) be used?

220.14(A) Whatever is the largest calculated load.

Specific Appliances or Loads. An outlet for a specific appliance or other load not covered in 220.14(B) through (L) shall be calculated based on the ampere rating of the appliance or load served.

 

[pv_n00b]

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."

This explains Women's Winter: https://youtu.be/d2NNm8MTboA

 

[pv_n00b]

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

The NEC requires a minimum power to receptacles (220.14(I)) that are not dedicated to a specific load. I have yet to run into an office space that has an outlet marked, "Workstation Only." So the NEC requires a minimum power that may be less than what is needed. That's cool because the NEC is not a design manual, you can go bigger just not smaller. Decide on a power budget for an office space that includes everything you think will be running at once and design for that, keeping in mind that the more power you provide the more expensive it will be to install.

Office kitchens are the worst. A pox on the person who puts the coffee maker, microwave, and toaster oven on the same circuit.

 

[ActionDave]

....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."

Nice story but I don't buy it, I've seen a bunch of cases like retirede described.