×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!
  • Students Click Here

*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

Jobs

Taps

Taps

(OP)
I was ref 240.21 in the NEC on tap conductors I know its legal to make taps. My question can I tap off some #500mcm feeders with a #8 to the primary side of a XFMR which has OCP for the primary.

RE: Taps

Length of the tap conductors, which you did not mention, is a determining factor as well as tap conductor ampacity rating as a percentage of the tapped circuit rating.  Delve a little deeper into the NEC and I expect you will find your answer, but #8 tapped to 500 MCM sounds pretty small to me......and if it is short, why not go with bigger wire?

Alan

RE: Taps

racobb has your answer -- I'll go one step further. If under 10 feet and field-installed, you have a "maybe" situation, since the ampacity of the tap conductors must be at least 1/10 of the upstream overcurrent protective device setting (not the ampacity of the feeder conductors) per 240.21(B)(1)(4).  Also, the overcurrent device protecting the feeder conductors cannot take advantage of the "next higher standard size" exception.

Read 240.21(B) and all of its sub-paragraphs thoroughly.

If you want more of answer, give us a wiring diagram and distances.

Good on ya,

Goober Dave  

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!


Resources