Sizing sub panel feeders & breaker


Old 02-10-00, 07:03 AM
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I am looking for info on sizing wire to feed a sub panel this is residential 220V single Phase I have installedf 100 amp 22 space panel which will have 15 20A 5 15A single pole & 1 60A 1 30A 2 pole breakers this is for general lighting and outlets in an addition as well as the 2 220 V breakers are for central a/c units. I have installed the panel & run 1 1/4 EMT to the main panel What i need is proper sizing & number of conductors as well as the breaker size to feed this panel from.

Any info would be greatly appreciated.
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Old 02-11-00, 01:53 PM
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put in a 100 amp 2 pole breaker in main panel and pull in the following
3- #3's check with local authority because here we can use #4 on subpanels 2 of which r your hots, 1 which u need to mark with white tape as your nutural, and a # 6 which u need to mark with green tape as your ground
Old 02-11-00, 08:51 PM
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I think you are oversizing, which is OK, if you plan on adding a lot later. But if you want to cut down on expenses a little you are going about it the wrong way. You conduit could be too small.
You should do the calculation first, that then determines size.
The fact you have 15 20 amp circuits is a little irrelevant. These could be one outlet circuits or could be 10 devices on a circuit.
Here is something to consider.
General use residential wattage is based on square feet. Whatever the size of your addition in sq ft, multiply by 3. Then simply add any stationary equipment, such as your ac. However, regarding AC, you only need to calculate the larger of the two, since these are considered non-coincidental loads. In other words they don't operate together.
If you are using a 60 amp breaker for your AC/Heat, you have at least a 12KW heat strip, as heat is usually larger than the cooling.
There is a chance that you could get by with less than a 100 amp service to your subpanel. That means smaller conduit, smaller wire size, smaller breaker, all at less cost.
Just points to ponder.
Old 02-15-00, 11:59 AM
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Thank you both for the info it was very helpful.

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