Parallel 90 degC conductors in conduit

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Immerkaer

Member
Location
Denmark
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

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
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

Senior Member
Location
India
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

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
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.
 
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