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Weird question about 90 conduit conductors vs. LB conduit bodies???

Weird question about 90 conduit conductors vs. LB conduit bodies???

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  #1  
Old 11-06-20, 07:10 PM
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Weird question about 90 conduit conductors vs. LB conduit bodies???

So how come there are all kinds of conductor restrictions for nice roomy LB conduit bodies but you can pull many more conductors through cramped 90 conduit connectors on the same circuit? This makes no sense to me and it's ruining my life. (I don't think I can change it either.)
 
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Old 11-06-20, 07:54 PM
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Can you explain that a little further or give us a link to the specific issue.
 
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Old 11-06-20, 08:59 PM
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Thanks again PJ. I am getting all tangled up over 314.28 and some stuff I read online.

I have two conduits:
A. I want to pull two 6-AWG THHNs and one 4-AWG THHN through 1" EMT or FMS
B.I want to pull six 8-AWG THHNs and two 6-AWG THHNs through a different 1" EMT or FMS

Along the way there will be 90% turns, and both will pass through through different junction boxes.

Can I use LB conduit bodies for A and B if I use the EMT type conduit?

Do I need an 8-inch-long boxes for the 6/6/4 or can I just use a 4" box?

Am I missing anything code-wise?


This whole thing baffles me for some reason.

THank you!!!



That's 37.24% fill. Fine. I start it off with a 90 degree EMT connector coming from the box.

Now I want to turn a corner. I want to use an LB body as a pull box.

Do I run into trouble there? I read some stuff online about volume of the box, diagonal dimensions, etc. Maybe I have to use a 1-1/2" LB with a reducer?

And let's say I want to pass this EMT through a workbox to divert (not splice) wires into a different direction.
 
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Old 11-07-20, 06:39 AM
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If you are using removable covers, the rules change for the better (easier). I can't imagine those having an issue if the conduit fill is OK, and splices are not made.

“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)” as seen in part below:
  • 8–6 AWG 1 inches.
  • 4–3 AWG 2 inches.
 
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Old 11-07-20, 10:21 AM
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Thanks, Telecom guy. I researched that section of the Code and read it 20 times before posting and I still don't get it. If I use a normal LB, for 8 and 6 AWG conductors, a 1" trade size conduit body is not that deep. So what should I use?

Thanks for your patience.
 
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Old 11-07-20, 11:03 AM
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Sounds to me you are mixing up rules for conductor splices in a box vs. conductors passing through a conduit body. The fill for conduit bodies is found at the manufacturer website. The conduit fill from the NEC tables does not apply to conduit bodies. You may find that a LB carries less conductors than the same size in conduit does.
 
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Old 11-07-20, 11:09 AM
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Exactly! And I was wondering why the rules were more stringent for bodies (that you can open) than for, say, 90 degree connectors that you cannot. The possible inductance cannot be worse.

Anyway, if I use 8 conductors do I need to put boxes in every 360 degrees of conduit? How do you turn 90 degrees with 8 conductors that are at 39% fill in one inch conduit?
 
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Old 11-08-20, 04:06 AM
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Have you looked at the possible need to reduce the ampacity of the conductors due to the number in the conduit?
 
  #9  
Old 11-08-20, 09:31 AM
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Well, no. But thanks for alerting me. I think I have lucked out. (These are on 50 AMP/2 pole breakers, all inside a garage)

Conductor Type = Copper

Wire/Cable Type = THHN/THWN-2

Conductor Size = 8

Ambient Temperature = 78 - 86 F

#Current Carrying Conductors = 4 - 6

Number of Parallel Runs = 1

Ampacity = 40 Amps

Insulation Temperature Rating = 90 C

Termination Temperature Rating = 60 C

Results provided by Cerrowire at https://www.cerrowire.com/products/r...ty-calculator/
 
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Old 11-08-20, 10:54 AM
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6 x #8 THHN .0366 x 6 = .2196 sq in
2 x #6 THHN .0507 x 2 = .1014 sq in
1" conduit at 40% fill .346 sq in max. You're at .321 sq in.

You're using 2P50A breakers but the derating is showing 40A ?
 

Last edited by PJmax; 11-08-20 at 11:20 AM.
 

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