26401 Load and Feeder Calculations
The lighting load for a single family dwelling unit that is 1,650 square feet is ________ per NEC table 220.12
1,650sf x 3 va = 4,950va
A minimum general lighting load for office buildings to be calculated at ________ per square foot based on NEC table 220.12.
3.5 va per s.f.
The smallest size locking and grounding type receptacle that may be used to provide shore power for boats is ______ per NEC 555.19(A)(4) informational note
30 amps
What is the minimum demand required for the portion of a feeder that supplies 30ft of show window?
30ft x 200va = 6000 va
What is the minimum general lighting load in volt-amps per square foot required by the NEC table 220.12 for a store?
3va per s.f.
The demand factor for 50 shore power receptacles is _________ per NEC Table 555.12
50%
To be considered a _____________load a circuit must operate for at least ____ hours or more without interruption.
Continuous Load = 3 hours or more
When calculating the feeder load for a motor Control Center supplying several Motors per 430.24 you must ______ .
Determine the sum of all the motor loads plus 25% of the largest motor.
What is the Lighting Load Demand Factor for that portion of dwelling units (multifamily) where the genreal lighting and small appliance load exceeds 120,000va per NEC table 220.42?
Lighting Load Demand Factor exceeding 120,000va is calculated at 25%
The optional method for determining feeder size for schools is covered in NEC section ______ .
NEC section 220.86
What is a tap conductor?
When the overcurrent protection for a conductor is located on the load side rather than the supply side of a conductor, it is considered to be a tap conductor
When performing load calculations for farm buildings the load that must be included in the calculation at 100% demand must be at least _______ .
60 amps
A commercial kitchen with six or more pieces of kitchen equipment is subject to a demand factor of ___________ per NEC table 220.56.
65% demand factor
What is the demand lighting load for a 100,000 square foot hotel with no dining room or ballroom is ____ per 220.12 and 220.42 ?
72,000 va
What is the conductor ampacity for the feeder with a continuous load of 120 amps?
•120a cont. load x 1.25 = 150a
What is the total load center length for a tapped feeder with loads of 120a at 50 feet, 110a at 60 feet, 75a and 90 feet, and 70 amps at 150 feet?
•120a x 50ft = 6000 •110a x 60ft = 6600 •75a x 90ft = 6750 •70a x 150ft = 10,500 •6000+6600+6750+10,500 = 29,850 •120a+110a+75a+70a = 375a •29,850 / 375a = 79.6 ft load center length
Calculate the minimum ampacity for a theater serving the following 3 phase 460 Volt Motors: 10 horsepower(14a), 20 horsepower(27a), and 30 (40a) horsepower.
•14a •27a •40a •40a x .25 = 10a •14a+27a+40a+10a = 91a
What is the feeder ampacity for a three phase, 120/208 Volt subpanel with a connected load of 84,563 Volt amps?
•84,563 va / 208volts = 406.5522 •Don't forget it's three phase! = 1.732 •406.5522 / 1.732 = 234.89a
•What is the total load for a feeder serving •(4) 2 horsepower motors 7.5a •(3) 5 horsepower Motors16.7a •(1) 15 horsepower 46.2a motor •(1) 25 horsepower motor ? 74.8a •(all Motors are 208 volts)
•Use Table 430.250 •7.5 amps x 4 = 30a •16.7amps x 3 = 50.1a • 46.2 amps x 1= 46.2a • 74.8 amps x 100% = 74.8 •74.8a x .25% = 18.7a (add additional 25% for largest motor load) •30+50.1+46.2+74.8+18.7=219.8a or 30+50.1+46.2+93.5 = 219.8a
1.Calculate the combined General Lighting Load for a residence that is 1,650 square feet (220.12) with 2 small appliance branch circuits (220.52a) and one laundry circuit (220.52b). 2.Apply Demand factors from NEC Table 220.42 to the calculation.
1,650sf x 3 va = 4,950va 1500va x 2 = 3000va 1500va x 1 = 1500va •4950+3000+1500 = 9,450 Apply Demand Factors: 1st 3000 @ 100% = 3000va Remaining 6450va @ 35% = 2,257.5va 3000va + 2,258 = 5258va
Residential Small Appliance Branch Circuits must be rated at least __________ per NEC 210.11(C)(1).
1500 va
Residential Small apliance circuits must be rated at __________ per NEC 220.52(A)
1500 va
The demand lighting load for a 20,000 square foot motel with no dining room or ballroom is ____ per NEC 220.12 and 220.42
18,000 va
Calculate the ampacity of a 100kva transformer coneected to 480 volts, 3 phase.
•100kva x 1000 = 100,000va •100,000va / 480v = 208.333 •For 3 phase transformers, you MUST include the square root of 3 = 1.732 •208.333 / 1.732 = 120.28a
1. Use NEC section 220.14(K)(1)&(2) for banks and office buildings to calculate the volt-amps required for a 40,000 s.f. building. 2. Apply a demand factor per NEC Table 220.44 based on the larger demand load.
•1st 10,000va x 100% = 10,000va •remaining 30,000va x @ 50% = 15,000va •10,000va + 15,000 = 25,000va
Using the Volt amps per linear foot method, the total Volt amps that must be used in a service calculation for a 50 foot show window is ____ per NEC 220.43(A).
•200va x 50ft = 10,000va •"Total" means include Continuous load • 10,000va x 1.25 = 12,500va
Calculate the minimum ampacity for a feeder serving 4 seperate motors all on a 480v 3 phase feeder: 2 motors rated 15 horsepower(21amps ea.) 1 motor rated 25 horsepower (34amps) 1 motor rated 40 horsepower (52amps)
•21a •21a •34a •52a •52a x .25 = 13a •21+21+34+52+13 = 141a
The ampacity of 4/0 THHN copper conductors is 260a. Using table 310.15(B)(3)(a) calculate the adjusted conductor ampacity for a raceway with 6 current carrying conductors installed.
•Apply adjustment factors for multiple current carrying conductors •Table 310.15(B)(3)(a) •4-6 ccc @ 80% •260a x .8 = 208a adjusted ampacity
The minimum ampacity for a feeder supplying (30) shore power receptacles in a marina each rated at 30a is _____ per NEC table 555.12.
•Table 555.12 •15-30 receptacles @ 70% •30 receptacles x 30a = 900a •Apply the demand factor from 555.12 900a x 70% = 630a
The minimum ampacity for a feeder supplying ten 30a shore power receptacles in a marina is _____ per NEC table 555.12
•Table 555.12 •9-14 receptacles @ 80% •10 receptacles x 30a = 300a •Apply the demand factor from 555.12 300a x 80% = 240a
