Subpanel wire sizing

Reply

  #1  
Old 09-13-13, 12:28 PM
braether3's Avatar
Member
Thread Starter
Join Date: Nov 2009
Location: wisconsin
Posts: 415
Subpanel wire sizing

Im installing a new subpanel to replace a old 3 wire fused subpanel, I will be running 1.5 or 2 inch conduit from the main panel outside into the garage attic and down into the basement, roughly 50 feet


Would 3-3-3-8 be the correct wire size for copper, 2-2-2-4 for alumnium?

Since most of the distance is through a open attic in the garage what would my options be with aluminum/copper service entrance cable? Xhhw? Conduit sleeve outside of course


Ben
 
Sponsored Links
  #2  
Old 09-13-13, 05:08 PM
Member
Join Date: Jun 2012
Location: USA
Posts: 1,036
How many amps does your sub really need? 3 cu would be good for 100, 2 al for 90
 
  #3  
Old 09-13-13, 07:39 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,397
Since most of the distance is through a open attic in the garage what would my options be with aluminum/copper service entrance cable? Xhhw? Conduit sleeve outside of course
You didn't say how many amps you wanted to feed the subpanel with, but judging by the conduit sizes you mentioned, I would suggest a 90A 2P breaker and #2 aluminum SER cable. That would give you three insulated #2 conductors and a #4 bare ground. SER cable is a service entrance cable and does not require conduit unless it is subject to physical damage. Many AHJs will allow you to protect #2 aluminum with a 100A breaker as #2 aluminum is suitable for a residential 100 amp service.
 
  #4  
Old 09-13-13, 09:01 PM
braether3's Avatar
Member
Thread Starter
Join Date: Nov 2009
Location: wisconsin
Posts: 415
Sorry I didn't specify on my amperage, 100 amp panel needs to be fed by 90/100 amp breaker this is the "main" Panel for the house.

Outside the house has 2 meters each with a service panel one for electric heat and one for the other loads each feed 100 amp breaker running into the house feeding a fuse panel and a breaker panel neither the fuse panel or the breaker panel have a neutral both relay on a bonded bare ground wire

Anyway the fuse panel has to go in order to sell the house

The cable would only be subject to damage outside down into the meter so it will be sleeved


Thanks guys
 
  #5  
Old 09-14-13, 03:32 AM
Member
Join Date: Jun 2008
Location: VA.
Posts: 813
Here's a scenario that would have to be used around here, if I was doing this job.

1) Upgrade service(1 meter) and install a 200 amp panel inside to replace one the existing panels, if within 6 foot rule. Then, replace fuse panel and feed off main panel.

2) Install 200 amp outdoor panel and feed both subs off of that.

3) Install 2-100 amp disconnects at meter and feed the 2 panels from those.

As Joe stated, some AHJ's allow #2 Al as mine is one of them.
 
  #6  
Old 09-14-13, 06:30 AM
braether3's Avatar
Member
Thread Starter
Join Date: Nov 2009
Location: wisconsin
Posts: 415
The beauty of 2 panels is the second One is all load management and is 5 cents a kw off peak
 
  #7  
Old 09-14-13, 07:37 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,397
The beauty of 2 panels is the second One is all load management and is 5 cents a kw off peak
I suspected you had a good reason for two meters; I'd want two also. What is the age and condition of the two meter sockets (or is it a single 2-meter socket)? What is condition of the service wiring up the the weatherhead? You might need to replace the entire service. Today you need 4 wires between the 100 amp disconnects and the two subpanels; the SER cable provides you the three insulated and one ground.
 
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
Display Modes