LB sizing

[ATI]

I recently installed a 200A 3phase service across the back of a building. I ran 4 250XHHW conductors to the panel, along the way through 2 - 3" standard aluminum LB's. I was bounced for sizing of the LB's, but I oversized the conduit for the LB's. I've run a similar set-up many times and never have been bounced for the LB sizing.
So to the question, I can not find the formula for a LB body to calculate fill. I know from LB specs I can run 3 - 250's in a 2.5" ( even though I ran 3" ), but I need the formula for 4 conductors.

Thanks for any help or pointers

 

[raider1]

When sizing an LB you size it the same way as you do a junction box using the conduit size when the conductors installed are 4 AWG and larger. This would require that the entries on the LB be 18" apart for a 3" LB (See 314.28(A)(2)).

Now with that said 314.28(A)(3) permits an LB to be smaller than the dimensions specified in 314.28(A)(1)&(2) where the conduit body has be listed for, and is permanently marked with, the maximum number and maximum size of conductors permitted.

Chris

 

[K8MHZ]

When sizing an LB you size it the same way as you do a junction box using the conduit size when the conductors installed are 4 AWG and larger. This would require that the entries on the LB be 18" apart for a 3" LB (See 314.28(A)(2)).

Now with that said 314.28(A)(3) permits an LB to be smaller than the dimensions specified in 314.28(A)(1)&(2) where the conduit body has be listed for, and is permanently marked with, the maximum number and maximum size of conductors permitted.

Chris

A quick check showed that a 3 inch Red Dot rigid LB is only 10 1/2 inches long.

 

[Dennis Alwon]

A quick check showed that a 3 inch Red Dot rigid LB is only 10 1/2 inches long.

Yes but if you read inside the lb it may state that it will take 4- 4/0 or something to that effect. If the LB is labeled for the wire size then you don't have to follow art.314 bending rule.

 

[K8MHZ]

Yes but if you read inside the lb it may state that it will take 4- 4/0 or something to that effect. If the LB is labeled for the wire size then you don't have to follow art.314 bending rule.

The nomenclature said 3-400's were the max. No indication about 4 conductors. I would presume that the same info would be marked on the fitting.

 

[K8MHZ]

Yes but if you read inside the lb it may state that it will take 4- 4/0 or something to that effect. If the LB is labeled for the wire size then you don't have to follow art.314 bending rule.

What voltage are we talking? Conductor bending radius requirements only apply to over 600 volts.

 

[K8MHZ]

I still am looking for an article that dictates that even if the pipe is sized correctly and the body is the same size as the pipe, there exists a possibility of the body being too small.

 

[Dennis Alwon]

What voltage are we talking? Conductor bending radius requirements only apply to over 600 volts.

I was talking about box size-- sorry. angle pulls is where the bend came from. I would think if you can get 3-400kcm you should be allowed the same volume with 4 conductors of a smaller size.

 

[Dennis Alwon]

I have seen where they ran 3" conduit and used a 4" lb and reduced down.

 

[K8MHZ]

I have seen where they ran 3" conduit and used a 4" lb and reduced down.

Me too, I have also seen inspectors require mogul fittings instead of regular ones.

But, for the life of me, I can't find anything in the book that says why.

 

[ATI]

Ok so I found what I was looking for from the distributor, but I have on last question. The LB is marked for 3*250MCM conductors. The info I have says the LB is rated as long as I do not fill more than 25.2%. With some simple cross multiplication and there info 3*250 mcm fill = 16.47 % of a 3" LB. If I ran 4 through the LB it would be 21.87% of the LB. I am under the 25.2% they require but the LB is not permanently marked with the 4 conductors being allowed (all conduit bodies are rated for 3 conductors) .
Is this an inspector call or do I have legitmate reason to ask for other opinions.
Thanks again

 

[K8MHZ]

I think I found it in 314.

The LB has to be 6 times as long as the raceway diameter unless complying with permitted conductor fill that is marked on the fitting.

 

[Dennis Alwon]

Ok so I found what I was looking for from the distributor, but I have on last question. The LB is marked for 3*250MCM conductors. The info I have says the LB is rated as long as I do not fill more than 25.2%. With some simple cross multiplication and there info 3*250 mcm fill = 16.47 % of a 3" LB. If I ran 4 through the LB it would be 21.87% of the LB. I am under the 25.2% they require but the LB is not permanently marked with the 4 conductors being allowed (all conduit bodies are rated for 3 conductors) .
Is this an inspector call or do I have legitmate reason to ask for other opinions.
Thanks again

Are you using 4 250 mcm conductors? If so I would say no good. If you are using 4 conductors that are smaller then I would think the fill would apply. I would be safe and check with the ahj. What makes sense to us does not necessarily work for the ahj.

 

[K8MHZ]

Ok so I found what I was looking for from the distributor, but I have on last question. The LB is marked for 3*250MCM conductors. The info I have says the LB is rated as long as I do not fill more than 25.2%. With some simple cross multiplication and there info 3*250 mcm fill = 16.47 % of a 3" LB. If I ran 4 through the LB it would be 21.87% of the LB. I am under the 25.2% they require but the LB is not permanently marked with the 4 conductors being allowed (all conduit bodies are rated for 3 conductors) .
Is this an inspector call or do I have legitmate reason to ask for other opinions.
Thanks again

Volume is not the issue. Take a look at 314.28(A)(3).

I would say that unless the LB is marked (and that includes both size AND number) for what you have in it, it will have to be 18 inches long, as previously mentioned.

The inspector seems to have been correct, unfortunately for you.

 

[K8MHZ]

Are you using 4 250 mcm conductors? If so I would say no good. If you are using 4 conductors that are smaller then I would think the fill would apply. I would be safe and check with the ahj. What makes sense to us does not necessarily work for the ahj.

I can't see where the NEC discusses fill, just length.

 

[ATI]

Correct, I understand the 6 * diameter of the pipe in 314.28. My dilemma is if I qualify under the exemtions in 314.28(3) smaller dimensions. The conduit body is not marked for the 4 conductors but is rated per manufacturer specs they gave me. Problem is conduit, wire and bodies are already installed and disassembling and reassembling would be catastrophe ( maybe a little exageration ).

 

[Dennis Alwon]

Correct, I understand the 6 * diameter of the pipe in 314.28. My dilemma is if I qualify under the exemtions in 314.28(3) smaller dimensions. The conduit body is not marked for the 4 conductors but is rated per manufacturer specs they gave me. Problem is conduit, wire and bodies are already installed and disassembling and reassembling would be catastrophe ( maybe a little exageration ).

I do not see an issue. Certainly you can 4 #10 wires in a 3" LB. I think fill is mentioned in the LB info that you mentioned -- so if it meets the percentage fill then I can't imagine it is an issue.

 

[augie47]

Me too, I have also seen inspectors require mogul fittings instead of regular ones.

But, for the life of me, I can't find anything in the book that says why.

I've wrestled with this a lot as the conductors identified in the conduit body seldom conform to the actual pull. I may be reading it incorrectly, but as I read 314.28(A)(3) as long as your conduit body is sized the same as the conduit and is filled less than allowed by Table 1, Chapter 9.
I was of the opinion that if the LB was marked (3) 500 XHHW you could not use (4) 350s as there was no cu in ruling, but as I see it now, if the wire fill is legal for the conduit, the corresponding conduit body is compliant.

I may be mistaken.

 

[raider1]

I've wrestled with this a lot as the conductors identified in the conduit body seldom conform to the actual pull. I may be reading it incorrectly, but as I read 314.28(A)(3) as long as your conduit body is sized the same as the conduit and is filled less than allowed by Table 1, Chapter 9.
I was of the opinion that if the LB was marked (3) 500 XHHW you could not use (4) 350s as there was no cu in ruling, but as I see it now, if the wire fill is legal for the conduit, the corresponding conduit body is compliant.

I may be mistaken.

The way I read 314.28(A)(3) is that you are permitted to have a conductor fill in the LB less than what Chapter 9 Table 1 allows provided that the conduit body is listed for, and is permanently marked with, the maximum number and maximum size of conductors permitted.

This section does not allow the LB to just be sized per Chapter 9 Table 1 it allows the manufacturer to specify the largest size and number of wires permitted in the LB provided that the fill does not exceed Chapter 9 Table 1 fill limits.

Chris

 

[Dennis Alwon]

This section does not allow the LB to just be sized per Chapter 9 Table 1 it allows the manufacturer to specify the largest size and number of wires permitted in the LB provided that the fill does not exceed Chapter 9 Table 1 fill limits.

Chris

So if the manufacturer tells you 25% fill are you saying that you can't have 4 conductors of a smaller size. Obviously you cannot be limit to 3 #12 if they state 3- 400KCM.