Can you apply demand factor to PC receptacles

charlie b

Moderator
Staff member
Location
Seattle, WA
Does "PC" refer to "personal computers"? If so, then yes I assign them a load of 180 VA each and I lump them in with other convenience receptacles when using the demand factor.
 

cppoly

Senior Member
Location
New York
Is there a place in the NEC that defines PCs as convenience outlets? I think that since PCs are on 24 hours a day in most commercial offices they wouldn't be considered convenience for the purposes of demand calcs. For a 100,000 VA of PCs a demand factor or not can make a big difference.
 

Smart $

Esteemed Member
Location
Ohio
Is there a place in the NEC that defines PCs as convenience outlets? I think that since PCs are on 24 hours a day in most commercial offices they wouldn't be considered convenience for the purposes of demand calcs. For a 100,000 VA of PCs a demand factor or not can make a big difference.
A convenience outlet under the NEC is called a general-purpose receptacle. Such a receptacle has no specific load.

The question I have for you is how do you determine the load of a computer?

FWIW, I have a computer with a 1200W power supply, a 30" LED monitor, three external hard drives, a modem, and a router connected to a UPS. The UPS says the system is currently consuming 250W... :huh:
 

Smart $

Esteemed Member
Location
Ohio
Good question about the load. I guess the only way to know for sure is see the current draw off of the PC nameplate.
That's sort of the point I was trying to make in my system only drawing 250W. I built my computer so it doesn't have a nameplate, but I know it has a 1200W power supply. AFAIK, the nameplate rating on a manufacturer built computer is likely to indicate the power supply rating, as that will be the worst-case current.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
PCs also remain on all day and should be continuous loads since they are on longer than 3 hours?
But they are not expected to be running at their maximum current for longer than 3 hours. So they don't meet the definition of a "continuous load."
 

cppoly

Senior Member
Location
New York
220.44 demand factor for receptacles apply only to 220.14 (H) & (I). Section 220.14 (A) Specific Appliances or Loads says an outlet for a specific appliance OR other load not covered in 220.14(B) through (L) shall be calculated on the appliance or load served. A PC is a specific appliance so wouldn't this fall into 220.14 (A)? Demand factor isn't applied to 220.14(A) so PCs wouldn't get a demand factor. Is this correct?
 

Smart $

Esteemed Member
Location
Ohio
220.44 demand factor for receptacles apply only to 220.14 (H) & (I). Section 220.14 (A) Specific Appliances or Loads says an outlet for a specific appliance OR other load not covered in 220.14(B) through (L) shall be calculated on the appliance or load served. A PC is a specific appliance so wouldn't this fall into 220.14 (A)? Demand factor isn't applied to 220.14(A) so PCs wouldn't get a demand factor. Is this correct?
I wouldn't call a PC an appliance, but that's moot as it is a load. There is no fault in your premise. IMO, this is an area of design decision.

Are the receptacles being installed specifically for the computers? ... or is it that you know the computers will be plugged in, but which receptacle is not known? Perhaps plugged in to the nearest receptacle. What other receptacles are on the circuit? What is the chances of nothing (significant) will be plugged in to those receptacles. If nothing, they still have to be calculated at 180VA (if not by area calculation).

So say you have two receptacles in the area, one is not used and the computer system is plugged into the other. If the computer system is rated 400VA but draws 240VA average under common usage, would the load on the electrical system be more accurately assessed by including (2 ? 180VA) or (240VA + 180VA) or (400VA + 180VA) in the load calculation?
 

cppoly

Senior Member
Location
New York
The receptacles on the drawings are labeled as PC receptacles and will be installed specifically for computers. Any PC can be ordered so a specific load will be unknown but design for panel schedule calcs are 360 VA per PC receptacle. For a huge area with tons of PC receptacles, feeder calcs can either be 55,000 VA w/ demand factor or 100,000 VA without demand factor.

Also PC are non linear loads so increasing the neutral conductor and panelboard buss is a good idea.
 
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