minmum cable cost

[Dbronx]

Lets assume these are less than 50% liner load a 3awg for 100 amps, 2/0 for 200 amps, 300mcm for 300 amps, 500mcm for 400 amps, Two 4/0 in parallel for 500 amps. If the cable rating is 92% of OCD it is allowed, and to code. By the way what code artical is that, In the mean time I'll be searching in NEC 2008, that is the current edition for this SOW. Can give further details about this I will appreciate it.

PS I am new to the Mike Holt's Forum and have not expressed my appreciation to all who have replied to my posts in the past Thank a lot

 

[iwire]

I will be happy to help but I don't understand where you got 92% or the other numbers.

Lets assume these are less than 50% liner load a 3awg for 100 amps,

3 AWG copper is rated 100 amps at 75C which is the most common temp you would use.

2/0 for 200 amps,

2/0 copper is only rated 175 amps at 75 C and you cannot load it above 175 amps but 240.4(B) allow the use of the next standard breaker.

300mcm for 300 amps,

That is only rated 285 amps and you cannot load it above 285 amps but 240.4(B) allow the use of the next standard breaker.

500mcm for 400 amps,

380 amps

Two 4/0 in parallel for 500 amps.

Not even close, 350 amps and 350 is a standard size breaker so that is the max breaker you could use.

If the cable rating is 92% of OCD it is allowed, and to code.

It is not.

By the way what code artical is that, In the mean time I'll be searching in NEC 2008, that is the current edition for this SOW. Can give further details about this I will appreciate it.

PS I am new to the Mike Holt's Forum and have not expressed my appreciation to all who have replied to my posts in the past Thank a lot

If you can give more details we can help you out.

 

[Dbronx]

I will be happy to help but I don't understand where you got 92% or the other numbers.




3 AWG copper is rated 100 amps at 75C which is the most common temp you would use.






2/0 copper is only rated 175 amps at 75 C and you cannot load it above 175 amps but 240.4(B) allow the use of the next standard breaker.





That is only rated 285 amps and you cannot load it above 285 amps but 240.4(B) allow the use of the next standard breaker.






380 amps




Not even close, 350 amps and 350 is a standard size breaker so that is the max breaker you could use.






It is not.



If you can give more details we can help you out.

SOW means (Scope of work) you could call them project spcecifcations
I'm using table 310.16 75 degree colunm a 4/0 is rated at 230 amps X 2 = 460 amps

 

[iwire]

I'm using table 310.16 75 degree colunm a 4/0 is rated at 230 amps X 2 = 460 amps

I apologize, for some reason I read 4/0 as 2/0.

There is no '92% rule' I think what you may be looking for is 240.4(B) which in some cases allows overcurrent rating above conductor rating however the calculated / connected load is still required to be below the conductor rating.

 

[Dbronx]

Thanks for the reply and artical 240.4, and connected load I will keep in mind when sizing cables over here.