Self Help Forums

Go Back   Self Help Forums > Repair > Building Construction - Existing Home
Register FAQ Members List Calendar Today's Posts

Building Construction - Existing Home Building Construction Repair / Remodeling Ideas and Problem Solving Solutions

Reply
 
Thread Tools Display Modes
  #1   IP: 12.229.12.104
Old December 28th, 2002, 02:04 PM
dmangalo dmangalo is offline
Junior Member
 
Join Date: Dec 2002
Posts: 8
Default motor calculation/wire size 310-16

here is the question: what size wire copper thw is necessary for a 5 HP, single phase 230 volt motor?

here is my calculation:

motor = table 430-148 = 28 amps for 5 HP motor
28 * 1.25 = 35 amps

wire = Table 310-16 = #10 is listed @ 35 amps but has an astric which I beleive is for calculating derate fill of conduit not wire size
therefore I would have to use #8 which is rated @ 50 amps.

My question is: "Is this correct?"

Also whenever the FLA is given then the table in art 430 is disreguarded and the actual FLA is used to determine the wire size.
True or false?
Reply With Quote
  #2   IP: 148.78.243.121
Old December 28th, 2002, 02:38 PM
Wgoodrich's Avatar
Wgoodrich Wgoodrich is offline
Super Moderator

 
Join Date: Sep 2002
Posts: 7,383
Default

Read 430.6.1 and 2. That should provide your answer when to use the charts or name plate. Basically the only time you use the amp rating of the name plate is when sizing the overload protection per 430.6 and 430.32.

You are correct using table 430.148 for normal single phase motors to find the full load current rate of that motor then referring to 430.22 telling you to size your conductor ampacity by increasing the full load current found in table 430.148 by 125%. Then referring to TAble 310.16.

When you get to 310.16 don't forget to consider 110.14.C telling you if your conductor size hits 1 awg or smaller to use the 60 degree column regardless what your temp rating of your wire insulation or if larger than 1 awg use the 75 degree column never using the 90 degree column unless you are calculating ampacity deration then again once your calculation is done for ambient temp Table 310.16 at bottom of chart or more then 3 current carrying conductors in a raceway in Table 310.15.B.2.A.

Now you were right up to this point what you missed was the meaning of the asterik. The asterik states that UNLESS OTHERWISE MENTIONED IN THE NEC. This OTHERWISE MENTIONED IN THE NEC is referring to Chapter 4 of the NEC for motors, generators, and transformers. When using Chapter for such as this project concerning motors then you would use the 35 amps for 10 awg and ignoring the asterik altogether if you are designing your wiring for products controlled by rules in Chapter 4 for motors, transformers, or generators. However you do not ignore the derations required in table 310.15.B.2.A or ambient temp at bottom of chart in table 310.16. These derations still apply only you use the value in the chart to start your derations ignoring the asterik. Again you have the rule in Article 110.14.C concering the 60 degree column use even with motors. That rule still appies.

Hope this helps

Wg
Reply With Quote
  #3   IP: 12.229.12.104
Old December 28th, 2002, 05:12 PM
Anonymous Anonymous is offline
Senior Member 'Self Help Master with Distinction'
 
Join Date: Sep 2002
Posts: 1,999
Default

Once again you have proven to be very helpful.
This is a awesome website wich I am glad I found.
dmangalo
Reply With Quote
  #4   IP: 148.78.243.122
Old December 29th, 2002, 12:59 PM
Wgoodrich's Avatar
Wgoodrich Wgoodrich is offline
Super Moderator

 
Join Date: Sep 2002
Posts: 7,383
Default

Pleased to see you have seen benifit from what we have to offer. Hope one and all learn at least a little something. That is our goal.

Good Luck

Wg
Reply With Quote
Reply






Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
drive wire size jimjimmy Electrical = Industrial / Commercial/Power Distribution 0 January 31st, 2007 08:32 AM
Last Motor Problem Roger Electrical Exam Preparations 9 July 22nd, 2005 06:29 PM
Ground Conductor size for parallel SE Fineimages Building Codes - Residential 29 August 22nd, 2004 06:04 PM
Ground wire size for 100amp sub-panel dougs241 Electrical - Existing Home 3 October 22nd, 2003 01:39 PM
Correct size AC unit to use Anonymous Heating & Air Conditioning - Existing Home 12 October 1st, 2002 01:09 AM


All times are GMT -4. The time now is 03:55 PM.


Powered by vBulletin® Version 3.6.7
Copyright ©2000 - 2010, Jelsoft Enterprises Ltd.
(c) 2010 Self Help and More 'All Rights Reserved'
http://www.selfhelpforums.com