×
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

20 & 30hp 460V wire sizing

20 & 30hp 460V wire sizing

20 & 30hp 460V wire sizing

(OP)
I need a little help with my wire and conduit sizing.  I have a 30 & 20 hp 460V motors close to each other and wish to run the wires in the same conduit.  Both motors are less than 30ft from the starter (20hp) and VFD (30hp).  Would a #8 and #10 wire be the correct size for the 30hp and 20hp, and they can be ran together in a 1 1/2" conduit?

RE: 20 & 30hp 460V wire sizing

If both motors can run at the same time you need to de-rate the conductors if they are run in the same conduit.  

If you are in the US:  Check NEC Article 310 for the required derating, and size each conductor for 125% of the motor full load amps in NEC Article 430, after applying the de-rating factor.   

Then size your conduit for maximum fill of 40%.

Don't forget the ground wires.  

RE: 20 & 30hp 460V wire sizing

(OP)
Thanks dpc, but the motors must run independently of each other.  

RE: 20 & 30hp 460V wire sizing

Are you saying the motors CAN run at the same time or CANNOT run at the same time?  

RE: 20 & 30hp 460V wire sizing

(OP)
the motors are running two different conveyors, although the motors are side by side.  They are controlled by two independent controls.  They may or may not run at the same time it is according when they are needed.

RE: 20 & 30hp 460V wire sizing

Then you must de-rate the conductors as I mentioned in my first response.   

RE: 20 & 30hp 460V wire sizing

(OP)
So then I will be at #6 for the 30hp and #10 for the 20hp.  I am I correct on that.

RE: 20 & 30hp 460V wire sizing

For the 20 hp: Take 125% of the Full load amps in the NEC table in Article 430.  Divide that by 0.8 to account for the de-rating required in Article 310 for up to 6 current-carrying conductors in a conduit.  The ampacity of the conductor must be at least this high.  I believe the #10 is too small.  

If you want to post how you came up with your numbers, we can  give you some additional help.  

Cheers,

Dave

 

RE: 20 & 30hp 460V wire sizing

(OP)
30hp at 40FLA so 125% gives 50Amps
20hp at 27FLA so 125% gives 34Amps
AWG #3 THHN is 110 Amps
AWG #8 THHN is 40 Amps (but according to the astric it can only be 30 Amps)
AWG #6 THHN is 55 Amps

So looking back over everything you are right the 10 would be to small, so it looks like #3 and #8.  And if I pull (4) #3 and (4) #8 @ 40% fill then I will need 1 1/4" Conduit.

RE: 20 & 30hp 460V wire sizing

Unless you use cable that is significantly shielded for use in VFD circuits, I would NEVER run cables from a VFD to a motor in the same conduit as anything else.

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