we're going to do an example of a dwelling unit load calculation to size a service this example is a printed thing that you'll have available to you the example says this says using the general method of calculation which is what we're talking about we're not talking about the other optional we're talking about the general method it says calculate the 120 240 volt service size for a single family dwelling we're talking about a multi-family we're not about duplex quad flex none of that single family dwelling in essence a a house a single family house we've got all these different pieces and parts it says unit with the following well we've got 1452 square foot living area typical smaller home we got a 9.6 electric heat at 240 volts we got a 5 horsepower ac unit at 240 volts a 1200 va volt amp dishwasher at 120 volts half horsepower disposal at 120 volts 4.5 kw water heater at 240 volts a 4.0 kilowatt closed dryer 240 volts and a 15 kw of range at 240 volts using our dwelling unit calculation with a nine step format we're going to do this and i'm going to put it on the board step one step two step three always step nine we're gonna do them slowly so our first part is step one we're just gonna do the format and i do want you to do just step one by itself stop so our step number one says three va per square foot our square foot is hundred and fifty two we just simply multiply that a simple calculator a little cheap one take three va or three multiply by fourteen hundred fifty two square foot that equals that gives us a number our number is 4 356 and that equals ba so that's step number one step number one is now complete now we look at our step number two small appliance two times 1500 va and laundry at 1500 v8 the code requires that there's two small appliance branch circuits and there's one laundry brand circuit so step number two says we got laundry and we got small appliance the laundry is 1500 va the small appliances is times two at fifteen hundred so two times fifteen hundred is three thousand right then step number two is taken care of now step number three tells us to go to a different table so let's go to table 220.42 it says apply line demand to steps one and two so what we're doing is we're taking all we've got we add it up we got a six we got a five we've got an eight and we got an eight right that's total v8 what step number three tells us to do is use the demand factor table which is table 220.42 and the demand factor table tells us the first three thousand we're going to keep at 100 percent anything above 3000 up to 120 000 is going to be at 35 so the 100 piece is 3 000. the best way to do that is just take that 3000 and subtract it set it off to the side and keep it we're making a keep roll over here we're going to keep that what we got left we got 5856 [Music] that's the first three thousand we're going to keep it and the remainder we're going to multiply it by 35 percent cheap flow calculator 5 856 [Music] and we're going to multiply it by 35 and that gives us 2049.6 that's step number three we're going gonna keep that too we're gonna keep this two thousand forty nine point five and keep that over here so these two combined equals steps one two and three that's taken care of now for step number four we're going to look at what step number four tells us step number four tells us we're going to compare the heat against the ac and omit the smaller well with our list of things that we have our heat tells us this tells us that we've got electric heat at 9.6 kw our ac unit is 5 horsepower at 240 volts we gotta do a sidequest uh because we've got heat that's in represented by kw just so we all understand our v8 is the same thing as wattage kw is a thousand watts so our 9.6 actually is 9600 watts or 9600 volt dams same thing we've got representation of our heat in the right format but we don't have representation of our air conditioning in the right format we got to convert it to kw and how will we do that we've got to go back to our motor section find out an opacity and use our formula wheel now our formula wheel we've got uh the top one says e squared over r well r is for ohms that's resistance over here we got i squared times r again r is resistance the e is voltage the i is amperage we don't have resistance listed anywhere here so we've got this e times i that's volts times amps hence the reason why it's called voltamps both amps is volts times m's we've already got the volts it's listed we need to convert that five horsepower into amps and how do we do that well we go back in our code book to article 430 and we go to article 430.248 248 table is an opacity based on horsepower based on voltage now we've got across the spectrum we've got voltages 115 200 208 230. well 230 is the same thing as 240. we got horsepower rated here and we're looking for something five horsepower okay five horsepower five horsepower at 240 volts it says it's 28 amps so now we've got our amperage known by looking at that table so our amperage for the five horsepower at 240 volts is 28 amps well 28 amps is i that's representation 240 volts is e so e times i equals watts which is the same thing as both dips right 28 times 240 is 7 six thousand seven hundred twenty six thousand seven hundred twenty and that's ba or watts now we're on step number four step number four says compare the heat against the air conditioning and we're going to keep the larger load and we're going to get rid of or omit the smaller load so in this case all this conversion for that air conditioning tells us that our number is six thousand seven hundred and twenty well nine thousand six hundred is definitely larger so we're going to keep the heat so step number four we're going to keep it over in our keep pile at 96 100 and we're going to call that heat it's gonna be step number four and we're keeping that we're getting rid of the air conditioning that was step number four let's look at step number five step number five tells us we're gonna look at all of our different appliances and if we got four more and then they're fixed that are not cooking or drying equipment or heat or air then we can take a 75 reduction of all the name plates well in our list of appliances we've got a 1200 va dishwasher then we've got uh a half horsepower disposal and it's at 120 volts then we got a 4.5 kw water heater and it's at 240 volts and that's all we've got that's not closed drying equipment or cooking equipment or heat or air we've got the same issue with this disposal as we had with the air conditioning the air conditioning we had to convert the horsepower into an amperage and then take the amperage times the voltage and come up with the v8 same process we're going to go back to article 430.248 and we're going to find it's a half horsepower and it's 120 volts cross reference it's 9.8 amps right so we take this 9.8 amps this little conversion here so it's 9.8 that's our i we got 120 times 120 that's our e and we're going to equal w or va 9.8 times 120 that equals 11.76 so 11 76 again that's watts or va we don't have four we only have one two three appliances so all we got to do with these we're going to just put them in our keep pile so our dishwasher is a 1200 va dishwasher our disposal which we now know is 1176. put that over there and our water heater which is 4500 same thing as 4.5 kw and that's step number five now we're gonna look at step number six step number six tells us dryers and remember dryers are 5000 minimum regardless of the nameplate unless the nameplace larger so we've got a dryer in our example that tells us that clothes dryer is 4.8 kw well we know that it's got to be at least five so this is a simple addition here so step number six just goes over here step number six we're gonna put 5000 for our dryer even though that we got a 4 000 list we're going to put 5 000. that's the minimum step number seven talks about that cooking equipment we have a 15 kw range so i'll write that up there and step number seven tells us we're going to go to table 220.55 well column c only applies to things cooking equipment that's not over 12 kw well we've got 15 kw that's over 12 kw so we gotta look see the notes so our note number one tells us that if it's over 12 kw through 27 the maximum demand and column c shall be increased five percent for each additional kilowatt of rating or major fraction thereof by which the rating of the individual range exceeds 12kw column c is based on 12. we got more than 12. so subtract 12 simple elementary math we got three what does that mean three five percent increases we could just simply go times three for the five and make it fifteen right column c for one range is the number is eight this is column c for one range is eight so we take that and multiply by fifteen percent more or you could do this because one times eight is eight right and then fifteen percent converted into a decimal format point one five you could do it that way and that's why i suggest that you do it for quick reference in math so take the 8 multiply by 1.15 that gives us 9.2 so 9.2 kw so all we're going to do with all this information is just go over here to our keep file right step number seven it's gonna be 9.2 or 9200 for the range step number eight says the largest motor is to be increased by 25 percent well our largest motor was the 5 horsepower motor right and that 5 horsepower motor was the ac remember the ac the ac was 28 amps times 240 volts was 67 000 or 6720 we're going to multiply that by 25 and see what that is because that's what step number eight tells us hey take the largest motor hit it by 25 and that gives us 1680. that's v8 v8 so down here at step number eight we're going to take this 25 we created here 11 sorry 16 80 and that's going to be 25 of the ac motor our last and final step is actually a two-step process and this is step number nine step number nine tells us the size of service by dividing the total va by the line voltage then apply to 310.12 table that's the first step so we're going to go over here we're just going to add them all up our keep pile now becomes very important we just add them all up so our first 3000 at the very top plus our 2049.5 the next one plus 9 600 plus 1200 plus 1176 plus 4500 plus 5000 plus 9200 plus 1680. i came up with a total of 37.405 point that's our total va for this single family dwelling unit that 1452 square feet with the appliances and the requirements according to the next letter code now we're going to do is convert that to ampacity now this is our conversion this is volt amps or what's we're going to divide that by our voltage right our voltage on the surface is 240 volts so this is our w or v8 this is our e right we're trying to find our i and we've got w and we got e so look w divided by e equals i that's the way this format works so we'll take our little calculator 37 405.5 divided by 240 volts i came up with a 155.85 and some more but that's okay that'd be rounded up to 156. that's our number that's the minimum service size we can have now with that being known we're going to go to that table 310.12 for dwelling service information well we've got the service sizes here that are the typical standards sizes we're allowed so 150 is the one of the numbers the next number up 150 175 we got to have at least 156 so 150 is not going to get it 175 would be the minimum requirement so 175 amp service according to national electric code is our answer what size wire does that have to be according to that table 3 10.12 if we're using copper we're going to use one oct and if we're going to use aluminum it'd be three ought aluminum your choice now the next piece on step number nine says what is the minimum size ground electroconductor that takes us to table 250.66 now that we know the wire size for the service we've got 250.66 we've got for copper we said one arch so why not takes us here if you look across for aluminum it's got we got ranges from number one to one ought in copper from number two out to three in aluminum for the ground electro conductor which we're going to use copper for ground electrical conductors for many reasons in the national electric code says number six so that is an example of a service calculation for a dwelling a single family dwelling unit don't get that confused because if you talk about a multi-family we've got more to do if we talk about a commercial application we've got more to do single family dwelling unit this is the nine step format there's a lot of steps a lot of pieces take them one by one don't combine them don't jump ahead and you'll come up with the right answer