×
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

Cable Size

Cable Size

Cable Size

(OP)
Hi everyone,

I am new graduate in electrical, if my question is very simple please forgive me in advance.

I am looking at ontario Electrical safety code, Table 1.
It says for single conductor 300MCM cable the ampacity is 480A (85-90 celcius)

On table 2 it says for 300MCM not more than 3 conductors in cable or raceway the ampacity is 295 (85-90 celcius).

On table 5B correction factors for table 1 it says for 3 conductors in contact the derating factor is 0.85

The question is this :
I am expecting that according tables 1, and 5B on table 2 the ampacity for one multiconductor cable (1c-3#350 MCM) be 480*0.85= 408A not 295A. and why table 2 is needed at all if the procedure for calculation is right.

I think I am missing something between multiconductor cables and single conductors.

Any help and references would be highly appreciated.

Regards,

Newcomer2005


RE: Cable Size

Table 1 is for an individual conductor in free air. If you read some of the rules, this table also covers individual conductors with an aluminum jacket.

Table 5B is a correction factor when individual conductors are put together in free air.

Table 2 is for conductors inside a raceway or cable, or in other words when there's another jacket or conduit covering the individual conductors.

Basically, the difference between single conductors and conductors in a cable or raceway is that the heat from the conductors in a cable or raceway has to travel through another barrier before reaching free air and the cables are all together inside this insulating barrier.

RE: Cable Size

(OP)
LionelHutz,

What is the ampacity of these two cases:

1)One cable three conductors (1-3/c-300MCM) in pvc conduit
2)three 300MCM cables (3#300MCM in pvc conduit

Thanks and Regards,

Newcomer2005

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