Conductor size

Reply

  #1  
Old 12-18-15, 12:22 AM
Member
Thread Starter
Join Date: Aug 2015
Location: Philippines
Posts: 77
Received 0 Votes on 0 Posts
Conductor size

Good day,

Sorry for asking but I was wondering what if the ampacity exceeds the ampacities on the table on the code. For example, if the computed ampacity is 900 A, what conductor size should I use?

This was not related to the chiller I post previously. I just wonder what if I got this large amount of ampacity.

Thank you to those who will answer.
 
Sponsored Links
  #2  
Old 12-18-15, 12:41 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 54,219
Received 477 Votes on 447 Posts
You're talking about a large service. You can get wire up to 1000mcm (about 600A) but you can't work with it. Anything over 500mcm is a bear to work with.

It depends on things like distance, pull points, elbows. It's what size can you pull comfortably.
You could run two parallel 600mcm (450A) but that requires massive conduit....two 4" conduits.
You could run three parallel 300mcm (300A) in three 3" conduits.
 
  #3  
Old 12-18-15, 09:21 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Generally anything that size will require an engineered design with stamped plans from an electrical engineer. The plans will spec out wire, conduits, panels, etc.
 
  #4  
Old 12-18-15, 08:53 PM
Member
Thread Starter
Join Date: Aug 2015
Location: Philippines
Posts: 77
Received 0 Votes on 0 Posts
I see. So this is what those parallel sets on plan. Anyone who knows about this parallel sets?
 
  #5  
Old 12-18-15, 10:37 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 54,219
Received 477 Votes on 447 Posts
Anyone who knows about this parallel sets?
What are you asking ?.......................
 
  #6  
Old 12-19-15, 10:22 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 10,231
Received 39 Votes on 31 Posts
Anyone who knows about this parallel sets?
Yep, numerous people on here.
 
  #7  
Old 12-22-15, 06:37 PM
Member
Thread Starter
Join Date: Aug 2015
Location: Philippines
Posts: 77
Received 0 Votes on 0 Posts
Give me some insights on how this parallel sets work. Thank you so much. need to gather some ideas.
 
  #8  
Old 12-22-15, 06:47 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 54,219
Received 477 Votes on 447 Posts
They don't make 900A wire.
So basically you would need to make two 450A runs. Two conduits next to each other with three wires plus ground in each pipe. Phase A, B, C and ground in each conduit.

However.... even that wire is too big to work with so you could run three conduits.
That would be three conduits with each one having three phases and and a ground.
You would use 300A wiring in each conduit.

Conduit 1 (300A) + conduit 2 (300A) + conduit 3 (300A) = 900A
Running three parallel sets of feeders requires special lugs as now each phase will be 3 wires.
 
  #9  
Old 12-23-15, 07:55 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
I'll add on one additional point that each parallel run needs to be as identical as possible in terms of length, route, materials, etc. Even small variations in one path can cause significant overloads on some of the conductors.
 
  #10  
Old 12-23-15, 07:19 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 10,231
Received 39 Votes on 31 Posts
As I recall, the ground wire with each set of paralleled conductors must be sized to the overcurrent device and not by the conductors it is run with. In other words, the ground must be full sized in each of the conduits. This could substantially increase the conduit size and would be a good case for using a conduit ground only.
 
Reply

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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: