DIYbanter - View Single Post - What size subpanel can I use for 150A Main panel

Pete C.[_3_]

wrote:

On Sun, 21 Sep 2014 10:07:53 -0700 (PDT), Mikepier
wrote:

There is no problem with a 100a sub panel on a 150a main. You would

feed that with #2 copper and off you go. You can protect the feeder

with a 100a breaker in the main panel and use an MLO sub panel as long

as you are in the same building.

The real limit is on the service as a whole. To know for sure whether

150a is enough you need to do a load calculation.

There are several load calculation templates on the internet you can

try.

If you have Excel the one from the city of Naperville seems pretty

good. There are 2 methods and they usually do not come out with the

same answer but you can use either one.,

Load calcs are something you measure with a micrometer, mark with

chalk and cut with an axe. Residential load calcs are just a wild

guess anyway. A frugal person would never get close to the calculated

load and a house full of people who never turn anything off will

easily exceed it.

Do I need to run #2 wire and use a 100A breaker? Or can I just run #6 to the sub-panel and use a 50A or 60A breaker in main?

Sure, the 100a is the max the sub panel can be used for but you could
use less if you want.
In residential, there are a lot of required circuits that might have
non coincidental loads. A lot depends on how many people are in the
house at any given time.

125A would be the maximum size you can use (with appropriately rated
wiring), that is the max branch circuit size allowed by code for
residential services. You'll have to special order 125A breakers though
as they are not common.