Wire Size Confusion

[JoanK]

Hi Guys,

New To the forum with first post.

We're installing a sub-panel in our garege to be fed with a 100 amp breaker (the sub panel is rated 125amps). The wire run is 40 feet, main panel is 200 amps. We installed the 200 amp main last year that passed Inspection.

We have all materials except the wire. The guys at Home Depot recommend to use 2-2-2-4 Alum SER, but the Electrical Inspector said that will only be rated for 80%. The Insp also said he can't really tell us what size to use.

This is causing the confusing.

Any help here???????

Thank in advance. NOTE: We would like to use COPPER SER ( will be easier to install for us).

JoanK.

[HayZee518]

the reason the inspector said the rating would be 80% is because according to code when you use 4 or more conductors the wire is derated a percentage of its full load carrying amps. Aluminum wire is doubled in size to its copper equivelant.
So, #2 copper ser is rated 130 amps. 80% of 130 = 109 amps. Use #2 SER copper with THHN as the insulation type. Wire size inside will be 2-2-2-4 - #4 will be the ground size.

[JoanK]

the reason the inspector said the rating would be 80% is because according to code when you use 4 or more conductors the wire is derated a percentage of its full load carrying amps. Aluminum wire is doubled in size to its copper equivelant.
So, #2 copper ser is rated 130 amps. 80% of 130 = 109 amps. Use #2 SER copper with THHN as the insulation type. Wire size inside will be 2-2-2-4 - #4 will be the ground size.

Thanks for the quick reply HayZee,

Have a happy Holidays. Thanks again