HOW TO DETERMINE SIZE FOR A HOME …

1 ANOTHERG & G ELECTRIC AND PLUMBING DISTRIBUTORS, SHEETCOPYRIGHT 19893 These How-To-Do-It sheets have been reviewed in June 2007 by a professional Engineer. If you find a problem, please notifyG & G Electric & Plumbing at 1900 NE 78th Street, Ste. 101, Vancouver, Washington 98665 HOW TO DETERMINE size FORA home ELECTRICAL SERVICEWhen replacing an old electrical serviceentrance or designing an installation for a newhome, one must be aware of current andfuture energy needs. Think about the myriadof kitchen appliances we take for grantedtoday that hadn t been imagined a fewdecades ago. Who would have thought spasand hot tubs would be common luxuries formany? Most RV s require 50 amp 240 voltcircuits to adequately power their will you be plugging in your car infuture years? home electrical services must be sized tomeet these demands. It is recommended thatno residence be served with less than a 100amp rated service entrance.

2 This becomes arequirement when the load exceeds 10,000watts or has 6 or more 2-wire branch size requirements vary according toarea, so we recommend that a careful check bemade before installing a services for residentialapplications are 100, 200, or 400 amps. Thegeneral rules of thumb for determiningservice sizes are: 100 amps will service a range, waterheater, general lighting, and receptacleoutlets. Usually recommended forworkshops, vacation cabins and largerpump systems. This amount of ampacity isreally too small for a residence unless gasheat and appliances are used. 200 amps will take care of range, dryer,water heater, general lighting andreceptacles, and a considerable amount ofelectric heat, while 400 amp services are designed for use inlarger homes that require over 20kW(20,000 watts) of electric heat plus all theaforementioned have drawn out a chart to help youdetermine your service requirements.

3 It isbased on Articles 220 of the 2005 NationalElectrical Code. The chart is very liberal inthat it uses a 100% demand factor on all ofthe heat load as well as on some of theappliances that might otherwise be figured ata lesser amperage. Minimum service size canbe found by adding up the total wattage thatwill be used, counting the first 10 kW at100%, and using a 40% demand factor on allthe rest. Once the calculated demand isdetermined in terms of wattage, divide thatby 240 volts to convert it into amps. Thiswould be your required service size . Pick fromthe standard services the one that is justabove your amperage requirement. (OVER)We suggest that you study Articles 220 and the examples in Chapter 9 of the NationalElectrical Code to obtain more information pertaining to service requirements.

4 Also,check with your local governing & G ELECTRIC AND PLUMBING DISTRIBUTORS, SHEETCOPYRIGHT 19893 These How-To-Do-It sheets have been reviewed in June 2007 by a professional Engineer. If you find a problem, please notifyG & G Electric & Plumbing at 1900 NE 78th Street, Ste. 101, Vancouver, Washington 98665 Column AColumn BColumn CColumn DRow ANational ElectricalCode ReferenceType of LoadLoad in Volt-amps (watts)Load in Amperes for a120/240 Volt ServiceRowCArticle 220-82 (B)(1)General Lighting/Receptacle Load based on Square-feet in residence. SF calculated by outer dimensionsof Dwelling excluding open porches, garages, orunused spaces not adaptable for future SF by 3VA/SF (3 watts/sf)_____RowDArticle 220-82 (B)(2)Small Appliance Branch Circuits (serve Kitchen,Pantry, Dinning Room or similar room s outlets)Minimum of two per Residence. Multiply number ofsmall appliance branch ckts by 1500VA (1500 watts)_____Row EArticle 220-82 (B)(2)Laundry Branch Circuits (serve Laundry room outlets)Minimum of one per ResidenceMultiply number of laundry branch ckts by 1500VA =_____Row FArticle 220-82 (B)(3) & (4)Nameplate rating of all appliances fastened in place,with a specific circuit, or motors (Name plate ratingscan be found on the appliance or obtained from MFR).

5 Electric RangesElectric DryersWater HeatersWall Mounted OvensCounter-mounted Cook topsDish WashersHot TubsTherapeutic TubsSauna/SpaPermanently fixed power toolsSwimming pool EquipmentCentral Vacuum_____RowGArticle 220-82 (B)Add the loads in Column C, Rows C through FSubtotal ARowHSubtract 10000 from Subtotal ASubtotal BRow IMultiply Subtotal B by CRowJAdd 10000 to Subtotal CSubtotal DRowKHEATING AND AIR CONDITIONINGRowLArticle 220-82 (C)(1)100% of Nameplate ratings of all air conditioningequipmentRowMArticle 220-82 (C)(2)100% of Nameplate ratings of all heat pumps withoutsupplementary electric heatingRowNArticle 220-82 (C)(3)100% of Nameplate ratings of all electric thermalstorage and other heating systems where usual loadis expected to be continuous at nameplate 220-82 (C)(4)Sum of 100% of Nameplate ratings of the heat pumpcompressor and 65% of the supplemental electricheating for the central space heating system.

6 Ifcompressor is prevented from operating at same timeas supplemental heat, it can be waived from the 220-82 (C)(5)65% of the Nameplate ratings of electric spaceheating if less than four separately controlled 220-82 (C)(6)40% of the Nameplate ratings of electric spaceheating if four or more separately controlled 220-82 (C)Largest of the values from Column C, Rows L thru QSubtotal ERowSArticle 220-82 (A)Add Subtotals D and FRowTDivide Subtotal F by 240 VTotal Ampacity =