Demand Load

[Piramyd]

Hi there

I'm electrical contactor, not engineer, so I would like someone explain me
how calculate the demand load that you see in many Panel Schedules done by engineers .
I just know the demand factor to size feeders that NEC require.
But which are the criteria you need to consider for calculate the demand load in particular panel subpanel. I browsed this forum and other but I don't find a satisfactory answer for me.
Thank you very much in advance.

 

[electrofelon]

Is this for plans such as required for plan review, or an actual schedule on the panel? If the latter, I don't really understand the purpose of those and if anything would be more inclined to put actual loads (where known) rather than NEC load calcs.

 

[Piramyd]

Demand Load

Well what I would like to know is :

1-Should it be the connected load less or equal to 80% of the panel bus rating?
If not, how bigger that 80 % of bus rating it can be?
2-I understand that you shouldn't load the panel more 80% of bus rating when it comes to continuous load. Is that right?

Thank you.

 

[LarryFine]

1. No, not connected load, that's everything. A load calculation takes into account things like AC and heat not simultaneous.

2. Correct.

 

[WA_Sparky]

General Understanding

General Understanding

For a better understanding you should jump to 220.10 (NFPA 70) to see how demand factors are applied. They change based load classification. Lighting, Receptacle, Motor, Kitchen Equip, Laundry Equip, XRay... There are many different classifications and concepts to grasp. Dwelling units are different as well. For commercial buildings there are a few typical ones that wont change.

Based on total loads in a given panel:
Lighting= Connected load *1.25 = Demand load
Receptacles (typically 180VA per receptacle unless specifically installed for a purpose then it takes that VA in your schedule.. computer, refrigerator, printer) = First 10KVA is 100%, then remaining * 40%. Example: 20KVA receptacle connected load. Demand = 14KVA (10KVA @ 100% + 10KVA*0.4).
Motors= 100%, Largest motor = 125% demand

Hope this help you understand it a bit better.

Your panel, OCPD, and feeder are sized based on total demand load for the given panel.

 

[topgone]

For a better understanding you should jump to 220.10 (NFPA 70) to see how demand factors are applied. They change based load classification. Lighting, Receptacle, Motor, Kitchen Equip, Laundry Equip, XRay... There are many different classifications and concepts to grasp. Dwelling units are different as well. For commercial buildings there are a few typical ones that wont change.

Based on total loads in a given panel:
Lighting= Connected load *1.25 = Demand load
Receptacles (typically 180VA per receptacle unless specifically installed for a purpose then it takes that VA in your schedule.. computer, refrigerator, printer) = First 10KVA is 100%, then remaining * 40%. Example: 20KVA receptacle connected load. Demand = 14KVA (10KVA @ 100% + 10KVA*0.4).
Motors= 100%, Largest motor = 125% demand

Hope this help you understand it a bit better.

Your panel, OCPD, and feeder are sized based on total demand load for the given panel.

Short of "KISS"ing it, the OP should learn how to classify each load. The demand factor for "continuous" loads should be 125%. "non-continuous" loads shall be treated at 100% demand.
For receptacle loads, please refer to:

• Table 220.44 (dwelling receptacles);
• Table 220.54 (household electric dryers);
• Table 220.55 (household electric ranges/ovens.. etc);
• Table 220.56 (electric heaters other than dwelling units);