Parallel 90 degC conductors in conduit

[Immerkaer]

Hi

My question is related to the derating rules applied to 90 degC cables.

When I am using a 90 degC cable in 40 degC ambient temp, I will apply correction factor 0,91 and check if this complies with 75degC conductor of same size.

Example:

Amb = 40 degC
Non-continous current = 100 A

90degC conductor - 3AWG : 115A x 0,91 = 104,65A
Check with 75 degC conductor 3AWG: 100A ampacity = OK to use 90degC 3AWG conductor.

For parallel scenario is:
6 current carrying conductors in conduit = 0,8 adjustment factor
30 degC amb = 1 correction factor

Non-continous current: 650A

2 x 500kcmil 90 degC conductors are chosen.
Total ampacity = 430*2*0,8 = 688A

Check with 75degC conductor: 380 x 2 = 760A --> OK
My question is, should I do the 75degC check as above or should I also add adjustment factors to the check as below?

380 x 2 x 0,8 = 608A --> NO OK.

Hope that my question makes sense to you.
Thanks in advance

 

[Dennis Alwon]

You did it correctly. The de-rating starts at the 90C rating of the conductor and the final ampacity would be at the 75C rating.

 

[Sahib]

The 90 degree cable with derating applied would operate at 75 degree or less temperature and that is reason derating not applied again at 75 degree IMHO.

 

[infinity]

Hi

My question is related to the derating rules applied to 90 degC cables.

When I am using a 90 degC cable in 40 degC ambient temp, I will apply correction factor 0,91 and check if this complies with 75degC conductor of same size.

Example:

Amb = 40 degC
Non-continous current = 100 A

90degC conductor - 3AWG : 115A x 0,91 = 104,65A
Check with 75 degC conductor 3AWG: 100A ampacity = OK to use 90degC 3AWG conductor.

For parallel scenario is:
6 current carrying conductors in conduit = 0,8 adjustment factor
30 degC amb = 1 correction factor

Non-continous current: 650A

2 x 500kcmil 90 degC conductors are chosen.
Total ampacity = 430*2*0,8 = 688A

Check with 75degC conductor: 380 x 2 = 760A --> OK
My question is, should I do the 75degC check as above or should I also add adjustment factors to the check as below?

380 x 2 x 0,8 = 608A --> NO OK.

Hope that my question makes sense to you.
Thanks in advance

Yes it's OK, you can use the 90° C ampacity for correction as long as it's a 90° C conductor.