Demand load calculation
- Thread starter Jimmy4645
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Thanks for the effort, Ekhlas. But you will allow me to observe that that spreadsheet was custom-designed for a project in your locality. The voltage levels are 380 phase to phase, and 220 phase to ground. The spreadsheet tabs are related to specific buildings and panels. The content of the various tabs includes specific equipment in your buildings that may not apply to other buildings in other projects. Therefore, the work that would be necessary to adapt the spreadsheet to other voltage levels and other project configurations would be prohibitive.
I will give you credit, in that this spreadsheet serves to illustrate the power and complexity that Excel can bring to a load calculation. But for my part, it is unlikely I will "borrow" it for use in any of my projects.
Hameedulla-Ekhlas
Senior Member
- Location
- AFG
Thanks for the effort, Ekhlas. But you will allow me to observe that that spreadsheet was ----------use in any of my projects.
Thanks Charli;
You can change its equipment and voltage just by editing it. It is password protected and its password is "yahoo".
Hameedulla-Ekhlas
Senior Member
- Location
- AFG
If you change only voltage rate, the 50Hz or 60Hz does not make any diffrence. But you have to edit and change it to your favorite.
Charlie said it very well. NEC 220.44 specifically states the demand factors of Table 220.44 can only be applied to receptacle loads that fall under 220.14(H) and 220.14(I). NEC 220.14(H) is plugmold and 220.14(I) is what I consider "convenience receptacles." IMHO, any other receptacle, including receptacles for hair dryers (either the fixed kind at the shampoo stations oe the portable kind at the styling stations), hair trimmers, curling irons, etc. would fall under 220.14(A), which is not permitted to use the demand factors afforded by 220.44.
The space is obviously pretty small - probably around 1250 square feet considering the lighting and HVAC loads. With a receptacle load of 15.48 kVA, that would equate to basically 86 "convenience receptacles" which would be highly unlikely in a tenant space this small.
I would recommend taking any receptacle that serves a specific load out of the "receptacle" load, calculating those receptacles serving those specific loads with a demand factor of 100%, and then applying the demand factor afforded by 220.44 to the remainder of the "receptacle" load. If I were to venture a guess, I think the result will come to 106 amps, as the receptacle load will become so small that the demand factors of 220.44 won't apply.
Also, I did not see where you accounted for the show window load as required by 220.43(A).
And as Charlie said, the circuit breaker only needs to be rated to carry 125% of the continuous load plus 100% of the noncontinuous load after demand factors have been applied.
stevenje
Senior Member
- Location
- Yachats Oregon
If my calculations are correct, that comes out to 86 "convenience receptacles" spaced out at a little over 1 1/2' apart. That should be enough!
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I would agree with your statement here, however, your quote does not match what was written. What was written is quoted as follows:
"More to the point, we are allowed to load the breaker to a total of (125% of the continuous" PLUS (100% of the non-continuous). "
Those two statements are NOT saying the same thing, hence why I asked where did Charlie derive that from.
NEC 230.42(A)(1) requires the ampacity of service entrance conductors to be not less that the sum of the noncontinuous loads plus 125% of the continuous loads when the OCPD is not a 100% rated device. Similarly, NEC 215.2(A)(1) requires the ampacity of feeders to be not less that the sum of the noncontinuous loads plus 125% of the continuous loads when the OCPD is not a 100% rated device. NEC Article 100 defines a continuous load as any load where the maximum current is expected to continue for 3 hours or more. Lighting is almost always considered a continuous loads, especially in occupancies such as this, because the lighting will essentially be on from open to close. Therefore, the lighting load is required to be multiplied by 125%.
Please see my reply in post #31. The code sections referenced in that post give the requirements for sizing the service and feeders conductors respectively. NEC 240.4 requires conductors to be protected in accordance with their ampacities with a few exceptions. Therefore, if the service conductors or feeders are rated at 125% of the continuous load plus 100% of the noncontinuous load, the OCPD can not exceed the ampacity of the conductors unless the installation falls under NEC 240.4(A) through 240.4(G).
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I'll be more clear, in post #6, it was stated you can load the breaker to 125% of continuous plus the non-continuous, i.e. you would be overloading the breaker in this case, or undersizing it, whichever point of view you want to take. Thanks for your help, although I am aware of the loading requirements, I was trying to get the poster of post #6 to realize the error without being too rude about it.
Apparently, they chose not to address the issue, although I imagine it was a just a misplaced word or two.
kwired
Electron manager
- Location
- NE Nebraska
I'll be more clear, in post #6, it was stated you can load the breaker to 125% of continuous plus the non-continuous, i.e. you would be overloading the breaker in this case, or undersizing it, whichever point of view you want to take. Thanks for your help, although I am aware of the loading requirements, I was trying to get the poster of post #6 to realize the error without being too rude about it.
Apparently, they chose not to address the issue, although I imagine it was a just a misplaced word or two.
He never stated a value for the breaker just values for the load, so he was not really wrong but not exactly easy to understand what he meant either.
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