Service wire ampacity

[dala]

I'm upgrading a service from 400amp 208volt 3 phase to 600amp 208volt 3 phase. I'm using 2 sets of 350kcmil thhn wires paralleled in 2 raceways. I calculate the adjusted ampacity of each set to be 560amps. Can you please explain to me why this is acceptable for a 600amp service?

 

[infinity]

If you're in separate raceways why do you have an adjusted ampacity?

Welcome to the forum. :smile:

 

[roger]

I'm upgrading a service from 400amp 208volt 3 phase to 600amp 208volt 3 phase. I'm using 2 sets of 350kcmil thhn wires paralleled in 2 raceways. I calculate the adjusted ampacity of each set to be 560amps. Can you please explain to me why this is acceptable for a 600amp service?

Well first of all, each set would not calculate to 560 amps, it would be the combined number of the two sets.

With that said see 240.4(B)

Welcome to the forum

Roger

 

[dala]

Because each each raceway has 4 current carrying conductors.

 

[dala]

Wouldn't each conductor derated to 80% current carrying capacity equate to 280amps? If so, wouldn't the parallel set equal 560?

 

[iwire]

Because each each raceway has 4 current carrying conductors.

Each raceway has 3 current carrying conductors.

 

[infinity]

Wouldn't each conductor derated to 80% current carrying capacity equate to 280amps? If so, wouldn't the parallel set equal 560?

You would if you had 4 CCC's but you likely only have three as Bob said. Take a look at 310.15(B)(4)(a).

 

[dala]

Thanks guys. You've been very helpful and it's much appreciated.