help sizing a junction box

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jwjrw

Senior Member
I need to size a JB for #1 conductors (3 rhw/3 thwn). The JB will have (2) 1 1/4" emt conduits in it. One in the bottom. One out the back. Can someone walk me through sizing the box correctly? I seem to be confusing myself once again.:confused:
 

Dennis Alwon

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Location
Chapel Hill, NC
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Retired Electrical Contractor
See if this helps. Wire size does not matter it is all about the conduit size.

ry%3D400
 

jwjrw

Senior Member
I think it confused me more.:grin:

Ok the "b" dimension must be 6 times 1 1/4" = 7.5 "
The "a" dimension shows 3 inches in table 312.6(a)
So is that a box 7.5" sq and 3 " deep?
 

Dennis Alwon

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Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I think it confused me more.:grin:

Ok the "b" dimension must be 6 times 1 1/4" = 7.5 "
The "a" dimension shows 3 inches in table 312.6(a)
So is that a box 7.5" sq and 3 " deep?


7.5 " is correct but the width can be less so you can have a 4x8 that is 4" deep. More common would be 8x8x4 but it does not need to be any wider than to accommodate the conduit.
 

jwjrw

Senior Member
7.5 " is correct but the width can be less so you can have a 4x8 that is 4" deep. More common would be 8x8x4 but it does not need to be any wider than to accommodate the conduit.



Thanks Dennis. It's been a while since I had to size a JB with conduit penetrations.
 

maghazadeh

Senior Member
Location
Campbell CA
I thought the dimension "B" 1 1/4" cond. multiply by 6 for angle pull = 7.5" supposed to be minimum distance for closest section of conduit entry to the other conduit entry. So the box height should be more than 7.5".
7.5"+1 1/4"+1"=9.75" or say 10"
I would use at least 12" hieght box.
 

Dennis Alwon

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Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Here is what it states

Exception: Where a raceway or cable entry is in the wall of a box or conduit body opposite a removable cover, the distance from that wall to the cover shall be permitted to comply with the distance required for one wire per terminal in Table 312.6(A).
The distance between raceway entries enclosing the same conductor shall not be less than six times the metric designator (trade size) of the larger raceway.

You would think the distance would be between raceways but it does not appear to be.
 
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