Residential Calculation 120/240 1 phase

[bryan kite]

Im wiring a 4000 square foot homeand need some help calculating the servise size.The appliances are mostly gas.There will be a 30 amp ac unit around 85 can lights, 15 regular light fixtures about 100 rec ,5 exhaust fans m,5 heat lamps. iI realise Im being vague . Ido mostly commercial work and its already calculated on the blue prints. Thanks in advance for any help Imight recieve.

 

[Nick]

Re: Residential Calculation 120/240 1 phase

That is an awful lot to post here. You should read article 220. It is pretty self explanatory if you understand the NEC. If you have specific questions post back for help. Personally I just don?t type fast enough.

 

[gardiner]

Re: Residential Calculation 120/240 1 phase

Hi try going here it might be helpful
http://www.mikeholt.com/documents/calculations/formulas/ResidentialLoadCalculations.xls

 

[jschultz]

Re: Residential Calculation 120/240 1 phase

4000sf x 3 va/sf = 12000
2 small appliance * 1500 va = 3000
1 laundry * 1500 va = 1500

sub total = 16500 va
first 3000 at 100% = 3000
next up to 120000 at 35% = (16500-3000)*.35=4725va

ac load = 30 amps x 240volts= 7200 va
other loads = ???? va
furnace load= 1/4 hp motor(guess) ???va
exhaust fans = ???? va
is it gas or electric dryer?
is it gas or electric washer?
is there any hot tubs, whirlpools, pools?
any heated floors or ceilings?
any other appliances in kitchen?(warming drawers, stand alone freezer, extra fridge, etc)
sewage ejector?
sump pump?
sauna?


total va= 3000+4725+7200+?????=14925va + ????
total amps= 14925/240=62 amps + ??? amps

[ March 03, 2003, 04:09 PM: Message edited by: jschultz ]

 

[mkbuck]

Re: Residential Calculation 120/240 1 phase

Bryan,

Take a look at the examples in Annex D, page 667 of the NEC. There are several examples of one-family dwellings with the Code sections referenced.

MKB

 

[z-men]

Re: Residential Calculation 120/240 1 phase

I just wired a 4000 sq foot house.A 200 amp service is plenty of power.You get a 40 circuit panel.You can also add a 100,125,or a 200 amp sub-panel to cut down on long home runs.Here is an easy way to get your load.Take a piece of paper and in one columb call that line one.In another columb call that line two.Say you have a 40 circuit panel and you have 15 single pole breakers on line one and 14 single pole breakers on line two.Change each single pole breake/circuit on line one to watts then add them up.Do the same thing to line two.If you have 240 volt circuit put 1/2 the watts on line one and 1/2 on line two.Add all the watts on line one and divide it by 120 volts,That will be your amperage on line one,Do the same for line two and get that amperage.For total power add line one and line two amperage and divide by 240 volts.You will be surprised how much power is left on the 200 amp panel.

 

[frenchelectrican]

Re: Residential Calculation 120/240 1 phase

bonsoir everyone ahh excuse me but i am new here with this forum here anyway i will cut the chase here and i did work on the 6,000 sq ft house not too long ago and the load demand what i figured out is very close for 200 a single phase but i put a sub feed on the oppise end of the house also to keep the run shorter and the second 6,000 sq ft house i working on now have 200 amps three phase the load demand figure are little diffrent than do with single phase i use the same formila with commercal buldings so it came close with it and the inspecter say that is plenty room with three phase normally i rather use 400 amps single phase

merci marc

 

[ron]

Re: Residential Calculation 120/240 1 phase

frenchelectrican,
If your calculation for the 240V single phase at the home was accurate, then the three phase will have a division of 1.73 (to account for the three phase). So if your calc was 200A for single pahse, then the three phase house will be 116A.
By the way, it is odd to have a residential service at 3 phase.

 

[jschultz]

Re: Residential Calculation 120/240 1 phase

it is a little odd to have three phase, but when you get above a certain ampere rating in some areas, they only offer 3-phase.
also, three phase is more common for multifamily residential high rise buildings where the condos are 10,000 sf.

 

[frenchelectrican]

Re: Residential Calculation 120/240 1 phase

yes indeed it is little odd in usa ( I am orginally from france) but this place i am working it was former commercal bulding and converted to residential setting and it allready have 3 phase service set up due the well pump it have very deep well it is over 250 meters deep!( little over 750 feet) the well have 5 hp 3 ph 480 volts there and have transfomer to drop voltage to the residental unit ( 120Y208 volts ) with large 75 kva transformer in electral room and i ran the feeder to panel box for it and yes i did type it wrong on formila i goofed on three phase i acctanaly use 240 volts insted of 208 volts my mistake i am sorry about my error and the panel box i ran is 150 amp ( trans sec. breaker is 200 a. ) but that place i working have 400 amp main service there ( 480 volts wye) and rest of the area i left the hids light at 277 volts that what it came with it i told my coumser he have 2 choice with hids to leave on 277 or swap with 120 v lights btw they are 400 watts MH low bays. to add more instering part that one section of bulding he use for fish farm with large 12,000 gal tanks ( that area allready change from emt to pvc due mostire in the air)


merci marc

 

[darren]

Re: Residential Calculation 120/240 1 phase

We use Article 220-30, Example #2, c. Also refer to Chapter 9 Tables and Examples; follow this example literally along with Article 220 for additional items, your goal is to provide accurate data to generate VA. Most often multiple A/C compressors will drive the potential load high.

We recently finished a 7500 sq ft home with an elevator and some other custom appliance features and this home calculated to accept a 200 Amp service (no heat/air conditioning, the demographics of high elevation do not require any air conditioning and the heat is with a boiler and floor tubes.

The most important part is accurate appliance information.

Hope this helps.

Darren

 

[jschultz]

Re: Residential Calculation 120/240 1 phase

if you have a 3hp motor for the elevator and electric oven and electric dryer, the 200amps would be really close, but would make it if you had no other large loads. All the large houses that we do tend to put in steam showers(electric) anywhere from 9kw to 30kw. So i would have put a 400 amp for that house to allow them some room to expand in the future. But i guess if they have gas appliances, then it would probably be fine as a 200.

 

[jmc]

Re: Residential Calculation 120/240 1 phase

Bonsoir, If you install a single-phase, 240/120 V, 200 ampere service, you will have 48 KVA available. If you install a 3-phase, 208/120 volt servic, you will have 70.7 KVA. More than enough power.