Ground pigtail wire size

Reply

  #1  
Old 07-17-17, 07:41 AM
N
Member
Thread Starter
Join Date: Jul 2017
Location: USA
Posts: 24
Received 0 Votes on 0 Posts
Ground pigtail wire size

I'm adding a new 240volt 30 A circuit and single receptacle. I pulled some leftover 4 gauge wire through 4 feet of FMC from sub panel to the box. What is minimum size of ground pigtail wire from main wire to the outlet and to the box? With 4 gauge I don't have a ton of room in this 4" square box.
 
  #2  
Old 07-17-17, 09:36 AM
A
Member
Join Date: Jun 2012
Location: USA
Posts: 1,650
Received 48 Votes on 43 Posts
It is stupid but you technically need to use 4 gauge to be compliant. The 30 requires 10 on all conductors so you need to upsize all proportionally.
You might be able to skip the pigtails completely and use a self-grounding receptacle.
 
  #3  
Old 07-17-17, 11:13 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,224
Received 105 Votes on 91 Posts
F MC is listed to 20 amp or less circuits for grounding.
 
  #4  
Old 07-17-17, 12:50 PM
T
Member
Join Date: Oct 2005
Location: USA
Posts: 1,693
Received 47 Votes on 46 Posts
If upsized due to voltage drop, right? But this is a 4' run?
 
  #5  
Old 07-17-17, 01:18 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,224
Received 105 Votes on 91 Posts
The ground needs to be increased by the same percentage anytime the other conductors are upsized, not just for voltage drop. This change happened in the last several code cycles.
 
  #6  
Old 07-17-17, 01:51 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,943
Received 44 Votes on 42 Posts
The ground needs to be #8 to match #4 hots. A standard 4x4" box is probably overfilled with those size conductors. You may need to add a box extender or bump up to 4-11/16" box.
 
  #7  
Old 07-17-17, 03:28 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,919
Received 1,344 Votes on 1,242 Posts
It would probably be easier at this point to replace the #4 wiring with #10 especially with the short run involved.
 
  #8  
Old 07-17-17, 06:09 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 13,808
Received 253 Votes on 221 Posts
F MC is listed to 20 amp or less circuits for grounding.
Only for circuits 6' or less AND 20 amp or less.
 
  #9  
Old 07-17-17, 06:28 PM
N
Member
Thread Starter
Join Date: Jul 2017
Location: USA
Posts: 24
Received 0 Votes on 0 Posts
Yeah this 4" box is already very filled at standard 2" depth. I don't know how you guys stuff everything in some of these boxes. It's like stuffing an alligator in an undersized sleeping bag sack tail first!

So go with the 4- 11/16" or a deeper 4" box?
 
  #10  
Old 07-20-17, 04:04 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: United States
Posts: 10,763
Received 97 Votes on 87 Posts
So go with the 4- 11/16" or a deeper 4" box?
You're only talking 4 feet. The price of the larger box and cover should easily cover the cost of buying #10 wire.
 
 

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