Receptacle and demand load

Status
Not open for further replies.
C

cppoly

Senior Member
Location
New York
For a commercial office, is it acceptable to consider all receptacles as general purpose receptacles and apply the demand factor for 100% first 10 kVA and 50% for remaining? All receptacles would include receptacles for printers, faxes, and other specific plug in equipment. Even though a printer is a specific appliance and according to the NEC it wouldn't get a demand factor, how often is a printer actually used? 10% of the time?

When sizing feeders, it doesn't seem practical to size a feeder based on 100% of the load for these plug in appliances. That would mean they are running almost all the time.

Thoughts?
 
S

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
cppoly said:
For a commercial office, is it acceptable to consider all receptacles as general purpose receptacles and apply the demand factor for 100% first 10 kVA and 50% for remaining? All receptacles would include receptacles for printers, faxes, and other specific plug in equipment. Even though a printer is a specific appliance and according to the NEC it wouldn't get a demand factor, how often is a printer actually used? 10% of the time?

When sizing feeders, it doesn't seem practical to size a feeder based on 100% of the load for these plug in appliances. That would mean they are running almost all the time.

Thoughts?
Click to expand...

I'm going to go out on a limb here. It depends (how was that for commitment?) Seriously, If I had a high end copier/printer that took 14 amps and a dedicated circuit was required/recommended then I would include its load. Otherwise, no. If Receptacles throughout were sparse and specifically designed to have operating equipment, then I would worry about it. However, most office designs have receptacles on three of the four walls of every 10 x 10 office, hallway receptionist etc. As long as the overall calculation yields more power than that which is required, and usually it is a lot more, and it slips by the building department, I don't really care.
 
C

cppoly

Senior Member
Location
New York
I should add I would include the full load of the appliance in the feeder calc, but instead of zero demand factor, I would apply the general purpose receptacle demand factor.

For instance, copiers would contribute 1,500 VA, faxes 1,000 VA etc. General purpose receptacles would be at 180 VA. So the total could be 100 kVA, but with demand, it would be reduced to 55 kVA.

As apposed to keeping 20 copiers on a floor at full load of 1,500 VA, when there's no way they would be on anywhere near running at close to 100%.
 
J

JDBrown

Senior Member
Location
California
Occupation
Electrical Engineer
cppoly said:
I should add I would include the full load of the appliance in the feeder calc, but instead of zero demand factor, I would apply the general purpose receptacle demand factor.
Click to expand...

I'm not sure this is allowed. Based strictly on the language of 220.44 and 220.14(H) and (I), I would agree with you, but the commentary for 220.44 is making me second-guess. For the benefit of those who don't have an NEC handbook handy, the commentary says the following:
Section 220.44 permits receptacle loads, calculated at not more than 180 volt-amperes per strap, to be computed by either of the following methods: 1. The receptacle loads are added to the lighting load. The demand factors (if applicable) in Table 220.12 are then applied to the combined load.
2. The receptacle loads are calculated (without the lighting load) with demand factors from Table 220.44 applied.
Click to expand...

The issue I have is that 220.14(H) and (I) say "not less than 180 volt-amperes", while the commentary says "not more than 180 volt-amperes". I realize that the commentary is supposed to be informational only, but my experience is that AHJs tend to treat the commentary as part of the Code (they do the same with fine print notes). Bottom line is, if the OP's AHJ interprets it the same way mine does, he may only be able to apply the demand factor to receptacles that were calculated at 180VA.

All that being said, the rule of thumb I usually go by is if a load is large enough to warrant its own circuit (vending machine, refrigerator, microwave, photocopier), I show the specific load on the panel schedule and don't apply the demand factor. Otherwise, I just call it a receptacle with a load of 180VA, and go ahead and apply the demand factor. I never know what exactly is going to go on each person's desk, so I couldn't really account for each PC, desktop printer, radio, electric pencil sharpener, cell phone charger, etc. anyway (I think that's the point of the 180VA per receptacle rule -- you don't know what's going to be plugged in).
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
cppoly said:
As apposed to keeping 20 copiers on a floor at full load of 1,500 VA, when there's no way they would be on anywhere near running at close to 100%.
Click to expand...
I would agree with you if the copiers were left powered on 24/7. But if they are turned off and then all turned on at roughly the same time, or brought out of power save by someone trying to use each one, then the heavy load for pre-heating the fuser area could hit all 20 at once. And that could last several minutes. From that point on you could assume that the heaters, etc. would cycle independently or only come on when the copier is in use.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
GoldDigger said:
I would agree with you if the copiers were left powered on 24/7. But if they are turned off and then all turned on at roughly the same time, or brought out of power save by someone trying to use each one, then the heavy load for pre-heating the fuser area could hit all 20 at once. And that could last several minutes. From that point on you could assume that the heaters, etc. would cycle independently or only come on when the copier is in use.
Click to expand...
Not just 24/7... what about where they are not on a UPS, or the backup exhausts its reserves? When the normal power is restored, and they are all still switched on, the same warmup condition occurs.

Another yet to be mentioned issue is that for offices, 220.14(K) applies for general-use receptacles (GUR's)... which forces the total VA to at least 1VA/ft?, before demand factor application.

Actually, I take issue with the wording and structure of 220.14... The general statement says 220.14 covers general use receptacles and outlets not used for general illumination. But then it says specific appliances and loads not covered in B-L... and L says not covered in B-K. In essence, it creates and endless loop of trying to determine which is what... or is that what is which. How can you have a specific load that's powered by a general-use outlet. (A) should be removed as a subsection and put in the general statement... ahead of the current general-use statement.
 
Status
Not open for further replies.
Top