Replies

1. 
   xxPaulCPxx | Feb 01, 2008 02:49am | #1

   They are looking for two things that I can think of:

   1.  What is the amperage you plan on providing from the subpanel?  Break it down to circuits and how many amps you intend to provide from this panel.
   Note, just because you have 5 20amp breakers doesn't mean you need a 100 amp panel ;).

   2.  How long will the wire need to be to reach from the main panel to your new subpanel - and how is it being run (conduit, raceway, bundles with other wire, buried underground.

   With those two numbers, load and distance, you will be able to calculate the correct gauge of wire needed to connect the two.  It might need a larger wire than normal if the wire is in a hot location (attic or bundle) or is far away (a shed 200' away)

   Rebuilding my home in Cypress, CA

   Also a CRX fanatic!

   If your hair looks funny, it's because God likes to scratch his nuts.  You nut, you.

2. 
   Stuart | Feb 01, 2008 03:31am | #2

   How about this one, posted right here on the Fine Homebuilding site:  http://www.taunton.com/finehomebuilding/PDF/Free/Service_Feeder_Calculations.pdf

   It's in the How-To section, look at the blue bar at the top of the page.

1. 
   BillHartmann | Feb 01, 2008 03:48am | #4

   Put can that be used for a sub-panel?The basic numbers can work (3 watts/sq ft, etc). But I don't think that you can take the demand factors. That is only good for an whole dewelling.I know that table 310.15(b)(6) reduced size for dewelling feeders, works like that..
   .
   A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

2. 
   woodway | Feb 01, 2008 06:41am | #5

   I tried to retrace your steps to find the "feeder calculations" table and I never did come up with the same table you did. How, step by step, did you go to the " how to" section to find that step by step table calculation?I tried the electrical section of "how to" and put in several word combinations to the search function and couldn't find that table. What am I doing wrong?

1. 
   Stuart | Feb 02, 2008 03:38am | #7

   I tried to retrace your steps to find the "feeder calculations" table and I never did come up with the same table you did. How, step by step, did you go to the " how to" section to find that step by step table calculation?

   How-to > Electrical > Design and Planning (in blue bar on left side of screen) > New Construction > Sizing an Electrical Service by Cliff Popejoy > View as PDF

   Edited 2/1/2008 7:38 pm by Stuart

1. 
   woodway | Feb 02, 2008 08:45pm | #8

   Perfect...Thanks

3. 
   pm22 | Feb 01, 2008 03:39am | #3

   This is a little form I drew up for a basic home calculation:

    

    

   Dwelling Unit Calculations

    

   (Use 120/240 volts)

    

   Step 1. General Lighting

   Area__________sq.ft. X 3 = ____________VA

   Small Appliances [2 X 1500]____3000____VA

   Laundry                    ____1500____VA

   TOTAL                      ____________VA

   First 3000 VA @ 100%       ___-3000____VA X 1 = _________VA

   3000 to 120,000            ____________VA X .35 _________VA

   Over 120,000               ____________VA X .25 _________VA

   TOTAL                                           _________VA à________VA

   Step 2. Appliances [Note: washing machine is included on the launder circuit.]

   Cold Water Heater     _________VA

   Dishwasher         _________VA

   Garbage Disposal     _________VA

   Trash Compactor     _________VA

   Other               _________VA

   TOTAL               _________VA   à or

   If more than 3         _________VA X .75 = à                     ________VA

   Step 3. Heat vs. Cold

   Air Conditioner @ 100%     _________VA

   Electric Heat           _________VA Largest à                   ________VA

   Step 4. Dryer

   5000 or Nameplate VA  [___amps X ___volts] [greater]     à       ________VA

   Step 5. Stove

   Result from 220-19 or 8000 VA à                                  ________VA

   Step 6.

   Total of 1 thru 5:                                         (6)________VA

        (6)_________  = (7) ________Amps

               240v   

   Step 7. Use Table 310-15(b)(6) if 120/240v

        Or use 310-16 [if 3 phase or above 400 Amps}

   Step 8.     Apartment = 100 Amp service

             House     = 200 Amp service

             Big house = 400 Amp service

   But for a subpanel, you would just need a list of all your expected loads. But I don't know why they would require calculations for a subpanel.

   ~Peter

4. 
   webted | Feb 01, 2008 08:58am | #6

   Hi K:

   I'm sorry I don't have it here to look at, but maybe someone else can verify this: isn't this included in the "code check" series of guides?

   http://store.taunton.com/onlinestore/item/070812.html

   If so, they're pretty good to have around, regardless.

   -t