Load Calculation Speed Drill

Load Calculation Speed Drill
©Ted “Smitty” Smith 2008,2011,2014,2017

STEPS FOR A SINGLE FAMILY DWELLING LOAD CALCULATION
1. General Lighting and Receptacle Load , and 2. Cooking Equipment 3. Electric Dryers 4. Fastened In Place Appliances 5. 25% of the Largest Motor 6. Largest of the Heating and AC load Remember when sizing service conductor for a dwelling unit to read (B)(7) and (C) STEPS FOR A SINGLE FAMILY DWELLING LOAD CALCULATION

Instructions This speed drill focuses on calculations that will be required for the journeyman and masters examination. To get the best benefit be sure the presentation is in slide show mode. The question slide will still transition in 3 ½ minutes and will be followed by the correct answer which will stay on the screen for only 10 seconds. Do not worry about writing down the correct answer during the transition. At the end of the questions, a stop slide will appear and then that will be followed by the questions and answers without the timer so you can review them. You must click on the screen icon in the lower right hand or left corner of the tool bar to start the slide show in order for the timer to operate.

Load Calculation What is the demand on the main service entrance of a single-family dwelling for the fastened in place appliances if the dwelling unit is equipped with a 2.1 KW volts, a 3.2 KW water 240 volts, a 4.6 KW air 240 volts, an electric furnace rated at 9.3 KW at 240 volts, an electric clothes dryer rated at V, a 14.1 KW electric range at 240 volts and a 1.1 KW garbage disposal at 120 Volts? The dwelling has 2952 square feet of habitable space. A VA B VA C VA D VA Copyright 2005 Ted "Smitty" Smith

Load Calculation B VA Step 4 of load calcs. Fastened in place appliances. 220.53 If there are four or more you can squeeze to 75%. You can not count electric dryers, electric cooking equipment, air conditioning equipment and heating equipment. There are only three in this house: 2.1 KW 120 volts, a 3.2 KW water 240 volts and a 1.1 KW garbage disposal at 120 Volts = 6400

Load Calculation What is the demand on the main service entrance of a single-family dwelling for the cooking equipment if the dwelling unit is equipped with a 2.1 KW volts, a 3.2 KW water 240 volts, a KW air 240 volts, an electric furnace rated at 9,3 KW at 240 volts, an electric clothes dryer rated at V, a 14.1 KW electric range at 240 volts and a 1.1 KW garbage disposal at 120 Volts? The dwelling has 2952 square feet of habitable space. A VA B VA C VA D VA Copyright 2005 Ted "Smitty" Smith

B VA Step 2 of load calcs. Cooking equipment 220.55 Note 1 If there is cooking equipment rated above 12 KW you should immediately write down the number of appliances, then draw an arrow and write down what it says for that number of appliances in Column C of  80000 Then under the line write the nameplate rating rounded off using normal rounding rules KW is 14  8000 14 Note one says to increase the value of column C by 5% for each KW or significant portion thereof that is greater than 12. We took care of the significant portion thereof by the rounding. If it had been .5 or greater then we would have rounded up. We now need to determine how many KW over 12 we are going to subtract 12 from the effective nameplate rating _____________________ 2 x 5= x 1.10= 8800

Load Calculation What is the demand on the main service entrance of a single-family dwelling for the electric clothes dryers if the dwelling unit is equipped with a 2.1 KW volts, a 3.2 KW water 240 volts, a KW air 240 volts, an electric furnace rated at 9.3 KW at 240 volts, an electric clothes dryer rated at V, a 14.1 KW electric range at 240 volts and a 1.1 KW garbage disposal at 120 Volts? The dwelling has 2952 square feet of habitable space. A VA B VA C VA D VA Copyright 2005 Ted "Smitty" Smith

Load Calculation A 5000 VA Step 3 of a load calc 220.54
Dryers must be taken at 5000 VA or their nameplate, whichever is greater and then a demand factor determined by Table applied to that. 1 appliance is 100% 5000 VA x 1= 5000 VA

Load Calculation What is the minimum number of 15 Ampere, V circuits required for the general receptacle and lighting loads of a single family dwelling if the dwelling unit is equipped with a 2.1 KW volts, a 3.2 KW water 240 volts, a KW air 240 volts, an electric furnace rated at 9.3 KW at 240 volts, an electric clothes dryer rated at V, a 14.1 KW electric range at 240 volts and a 1.1 KW garbage disposal at 120 Volts? The dwelling has 2952 square feet of habitable space. A. 2 B. 3 C. 5 D. 6 Copyright 2005 Ted "Smitty" Smith

Load Calculation C. 5 Not a standard step but it is part of Step 1
Habitable space x 3 2952 X 3= 8856 Convert power into amperes using ohms law P/E= A 8856/120=73.8 There is a minimum of 73.8 amperes of load for the general receps and lights. 73.8 A / 15 A= 4.92 There will need to be five 15 A circuits minimum.

Load Calculation What is the demand on the service of the general receptacle and lighting loads of a single family dwelling if the dwelling unit is equipped with a 2.1 KW volts, a 3.2 KW water 240 volts, a KW air 240 volts, an electric furnace rated at 9.3 KW at 240 volts, an electric clothes dryer rated at V, a 14.1 KW electric range at 240 volts and a 1.1 KW garbage disposal at 120 Volts? The dwelling has 2952 square feet of habitable space. A VA B VA C VA D VA Copyright 2005 Ted "Smitty" Smith

Load Calculation C. 6624.6 VA Step 1 of a Load Calc T 220.12
Habitable space x 3 2952 X 3= 8856 add 1500 VA for each small appliance branch circuit and laundry circuit =13356 220.42 First 3000 taken at 100% = 10356 Next 117,000 VA taken at 35% 10356 x .35= Now add back in the 3000 that has to be taken at 100% = VA

Load Calculation What is the minimum demand applied to the service for the largest motor in a single family dwelling if the dwelling unit is equipped with a 2.1 KW 120 volts, a 3.2 KW water 240 volts, a 4.6 KW air 240 volts, an electric furnace rated at 9.3 KW at 240 volts, an electric clothes dryer rated at V, a KW electric range at 240 volts and a 1.1 KW garbage disposal at 120 Volts? The dwelling has 2952 square feet of habitable space. ASSUME 100% of the MOTOR LOAD IS CALCULATED AS A LOAD IN ANOTHER PART OF THE LOAD CALCULATION. APPLY ONLY THE ADJUSTMENT FOR THE LARGEST MOTOR. A VA B VA C. 275 VA D. 960 VA Copyright 2005 Ted "Smitty" Smith

Load Calculation C. 1150 VA 250.50 Step 5
We have to take the largest motor at 125% of its current rating. 100% of the motor load is calculated as perhaps an appliance or heating and air conditioning equipment, etc. Therefore all we need to do is determine the largest motor and then apply a 25% adder. Remember, we don’t consider something a motor load unless the majority of the nameplate rating is motor. For example a dryer has a motor but the majority of the its nameplate rating is the heating elements. That would not be a motor load. In this building there are two: The garbage disposal and the air conditioner. The largest is the air conditioner x .25= 1150 VA

Load Calculation What is the demand of the heating and air conditioning equipment of a single-family dwelling if the dwelling unit is equipped with a 2.1 KW 120 volts, a 3.2 KW water 240 volts, a 4.6 KW air 240 volts, an electric furnace rated at 9.3 KW at 240 volts, an electric clothes dryer rated at V, a KW electric range at 240 volts and a 1.1 KW garbage disposal at 120 Volts? The dwelling has 2952 square feet of habitable space. A VA B VA C VA D VA Copyright 2005 Ted "Smitty" Smith

Load Calculation A. 9300 VA STEP 6 220.51
We can not squeeze heating and air conditioning loads. 220.60 If two loads will not be used at the same time on a service, then we only have to account for the demand of the largest of the two. Heating and air conditioning is one of the times we can use this rule. Heating 9300 VA Air Conditioning 4600 VA The largest is 9300 VA

Load Calculation What is the sized service required for a single family dwelling if the dwelling unit is equipped with a 2.1 KW volts, a 3.2 KW water 240 volts, a KW air 240 volts, an electric furnace rated at 9.3 KW at 240 volts, an electric clothes dryer rated at V, a 14.1 KW electric range at 240 volts and a 1.1 KW garbage disposal at 120 Volts? The dwelling has 2952 square feet of habitable space. A. 100 A B. 150 A C. 175 A D. 200 A Copyright 2005 Ted "Smitty" Smith

Load Calculation C. 175 A Add all the 6 Steps you have been doing
STEP 1 Lighting and Recep STEP 2 Cooking 8800 STEP 3 Dryers 5000 STEP 4 Fastened In Place Appliances 6400 STEP 5 25% of the Largest Motor STEP 6 Largest between Heat and AC 9300 VA divided by 240 Volts= Amps The next standard size service (240.6) is Amperes

Load Calculation What is the minimum sized RHH Aluminum service entrance conductor required for a single family dwelling if the dwelling unit is equipped with a 2.1 KW volts, a 3.2 KW water 240 volts, a KW air 240 volts, an electric furnace rated at 9.3 KW at 240 volts, an electric clothes dryer rated at V, a 14.1 KW electric range at 240 volts and a 1.1 KW garbage disposal at 120 Volts? The dwelling has 2952 square feet of habitable space. Assume all terminations are rated at 75 degrees C. A. 3/0 AWG B. 4/0 AWG C. 2/0 AWG D. 1/0 AWG Copyright 2005 Ted "Smitty" Smith

Load Calculation A 3/0 AWG
310.15(B)(7) allows us to size the conductor based on 83% of the service rating. The service is A 175 x .83= According to (C) we will need to size this service based on 75 degree C table because even though the wire is rated at 90 degrees C, the panel is rated at 75 degrees C. A 3/0 AL in the 75 c has an ampacity of 155 A.

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