Sizing feeders.

[Mr. M]

I was discussing with my apprentice the size of conductors required to supply power for a 200 amp., residential service.

I told him we are going to use 4/0 Al., per Table 310-15 (B) 7. Due to the fact that the sub panel is a good 10' away from the point of entry,

I'm going to install a 200 amp service disconnect at the point of entry. Then run 4/0 SER Al., to the sub panel. Grounding to h2o pipe with

#4 cu. and to ground rod with #6 cu. He thought we should use 250 kcmil. Comment?

 

[jumper]

Your sub panel carries the whole load of the building, correct?

If so, you are correct. GEC sizes are also good.

PS. You are showing your age. The NEC quit using dashes after the 1999 edition.

 

[Mr. M]

Thanks, L-O-L

 

[kwired]

I was discussing with my apprentice the size of conductors required to supply power for a 200 amp., residential service.

I told him we are going to use 4/0 Al., per Table 310-15 (B) 7. Due to the fact that the sub panel is a good 10' away from the point of entry,

I'm going to install a 200 amp service disconnect at the point of entry. Then run 4/0 SER Al., to the sub panel. Grounding to h2o pipe with

#4 cu. and to ground rod with #6 cu. He thought we should use 250 kcmil. Comment?

200 amps with aluminum conductor in a dwelling application is a bad example for showing differences between 310.15(16) and 310.15(7) results.

With 310.15(16) You still end up with 4/0 aluminum unless your load calculation is over 180 amps, which is the ampacity of 4/0.We are allowed to use next size up overcurrent protection of 200 amps as long as our load is 180 amps or less.

If you have a dwelling with a load calc over 180 amps - you are probably going to bring in at least 400 amps capability if you are a wise designer, and that likely will end up being at least 2-200 amp panels each with 180 or less connected to them.