×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

cable ampacity table NEC

cable ampacity table NEC

cable ampacity table NEC

(OP)
Hi,

I am trying to figure out the following:

- NEC article 392.80(A)(2)(c)state that for single conductors installed in a trifoil formation with separation of 1 diameter between individual conductors we should use table 310.15(B)(17) for ampacity. This table for example gives you an ampacity of 620 A for a 500MCM, 75 C conductor at 30 C ambient temp.

-NEC article 392.80(A)(2)(d)state that for single conductors installed in a trifoil formation with separation of 2.15 diameter between conductors we should use table 310.15(B)(20) for ampacity. This table gives you an ampacity of 496 A for a 500 MCM, 75 C conductor at 40 C ambient temp, or 560 Amp at 30 C ambient temperatura (using the corection factors of table 310.15(B)(2)(B).

My question is: Why if i separate the conductors 2.15 diameters, which is more than 1 diameter, the ampacity of the table i have to use is less? This make no sense to me, if this is the case, it will be better to separate conductors just 1 diameter and not 2.15.

Regards,
Cmed.

RE: cable ampacity table NEC

(c) refers to "single conductors" in a "single layer". Not sure what your definition of "trifoil" is, but I don't think (c) and (d) are referring to the same conductor configuration.

RE: cable ampacity table NEC

(A)(2)(c) is for a single layer. That is the conductors are all laying flat in the tray with a one diameter seperation between the conductors. It is not for a triangular configuration. The rule in (d) applies to triangular configuration.

RE: cable ampacity table NEC

(OP)
thanks DPC. Regards

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close