Another fun practice Load Calc

Konen

Member
Location
Washington
Occupation
01 Electrician
Single Family Dwelling
Use standard method of calculation
120/240v
Looking for minimum size THWN Aluminum conductors
Service Size?

30' x 60' dwelling space
Garbage disposal- 864va
Dishwasher- 1100va
Trash compactor- 1188va
Water heater- 4500va
Attic Fan- 750va
Swim pool pump- 1250va
Dryer- 4500va
Range- 12kw
Heat- 10kw @240v
A/C- 32A @240v

MY ANSWER:
150A Service
2/0 Aluminum for Line
#2 for the Neutral.
 
Location
USA
Occupation
Electrician
fulldemand
VAamps
square feet18005400
small appliance23000
laundry11500
Total lighting990022.56
dishwasher1100
disposal846
compactor1188
water heat4500
fan750
other 3
Total app838426.20
C cooking1200033.33
dryer450020.83
FESH 110000
pump1563
Total FESH2806348.18
Total151.11
*0.83125.42
2 / 0 AL135 amps
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
30' x 60' dwelling space
Garbage disposal- 864va
Dishwasher- 1100va
Trash compactor- 1188va
Water heater- 4500va
Attic Fan- 750va
Swim pool pump- 1250va
Dryer- 4500va
Range- 12kw
Heat- 10kw @240v
A/C- 32A @240v
What did you consider to be "appliance load" and what did you consider to be "motor load"?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Would it be wrong to include the swimming pool pump with the appliance load and if so, why?

Although the definitions of appliance is weak I don't see a pool pump as an appliance.

Appliance. Utilization equipment, generally other than industrial,
that is normally built in standardized sizes or types and is
installed or connected as a unit to perform one or more functions
such as clothes washing, air-conditioning, food mixing,
deep frying, and so forth.
 
Location
USA
Occupation
Electrician
I would exclude from appliances the attic fan, the water heater, and the pool pump.

The 2020 NEC now requires a minimum of ¼ hp or 500 VA for appliances. Too many 25 VA bath fans.

The water heater is clearly an appliance in articles 220 and 422.

How about instantaneous water heaters and car chargers?
 

Konen

Member
Location
Washington
Occupation
01 Electrician
The code states that the 83% is of the service rating not the load. So if you have a load of 151 amps the service could be 175 amps minimum

83% of 175 = 145 amp conductor which would be 3

The code states that the 83% is of the service rating not the load. So if you have a load of 151 amps the service could be 175 amps minimum

83% of 175 = 145 amp conductor which would be 3/0 as David stated
Good catch, I applies the 83% demand factor to both the service and conductors. I Calculated 154A which make it a 175A service.
 
Location
USA
Occupation
Electrician
Here is the commentary from the 2017 Handbook:

The main service or feeder to a dwelling unit is permitted to be sized at
83 percent of the disconnect rating. The calculation is not based on the
rating of the overcurrent device protecting the main feeder. The minimum
disconnect rating for a dwelling unit is 100 amperes according to
225.39 and 230.79. This calculation applies only to conductors carrying
100 percent of the dwelling unit’s diversified load.

If a 120/240-volt single-phase service supplies a one-family dwelling,
or an individual unit of two-family or multifamily dwelling, then the
reduced conductor size is applicable to the service-entrance conductors
or feeder conductors that supply a dwelling unit. The feeder conductors
to a dwelling unit are not required to be larger than its service-entrance
conductors.

Exhibit 310.5 illustrates where 310.15(B)(7) could be applied. The
reduced conductor size permitted is applicable only to the service entrance
conductors run to each apartment from the meters. The
reduced conductor size permitted is also applicable to the feeder conductors
run to Apartment 3 from the service disconnecting means,
because this feeder carries the entire load.



83 percent.PNG
 
Location
USA
Occupation
Electrician
Good luck.
Spreadsheets should be a large part of Article 220. Unfortunately, Article 220 was written before they were available and has not been revised to incorporate their usefulness.
 
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