The use of 'LB's

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warrenwaldrop

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It is my understanding after reading NEC Article 314-28(A)(3) that if I have conductors #4 and larger in a raceway and want to use an 'LB' that I have to comply with the markings inside the 'LB'. In other words if I do not violate the maximum quantity of conductors as marked on the inside of the 'LB', and do not have conductors larger then what is stamped on the inside of the 'LB' then I am in compliance with this code section.

Now if I have an 'LB' on a 3" raceway and have 4#250Kcmil & 1#2/0(G) and the raceway is marked, indicating that the maximum number of conductors allowed is three, and the maximum size conductor allowed is 400Kcmil. With this situation it is my understanding that I can not comply with this code section 314.28(a)(3).

Am I right? or what am I missing if I am wrong?

[ December 20, 2004, 03:46 PM: Message edited by: warrenwaldrop ]
 
Re: The use of 'LB's

Dave,
You would be allowed 1200kcmil TOTAL.
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Are you saying we can just use the total kcmil area without out looking at the number and size of the conductors? I don't think so. I'm not sure how you use an LB in the case that started this thread. The combination of wires to be installed is not covered by the markings on the LB. I think that in this case you have to comply with the rules in 314.28(A)(1).
Smaller Dimensions. Boxes or conduit bodies of dimensions less than those required in 314.28(A)(1) and (A)(2) shall be permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill (of conduits or tubing being used) permitted by Table 1 of Chapter 9,provided the box or conduit body has been listed for and is permanently marked with the maximum number and maximum size of conductors permitted.
Click to expand...
Don
 
Re: The use of 'LB's

Don,

When is the last time you saw an LB sized to (B)?

(A)(1),(2)and(B) are addressing "boxes" not "conduit bodies".

(A)(3) and (C) are addressing "conduit bodies".

Chapter 9 Table Notes for Table 1:
(6) For combinations of conductors of different sizes, use Table 5 and Table 5A for dimensions of conductors and Table 4 for the applicable conduit or tubing dimensions.

Area of 4 250kcmil and 1 2/0 ground.
Area x 4 = Total + Area = Total with ground.
256.1 x 4 = 904.4 + 143.4 = 1047.8

Area of 3 400kcmil = 1134.9
 
Re: The use of 'LB's

Dave,
I still find no permission to install the number and size of the conductors listed in the original post. The rules for combination of wire fill have to do with raceway size, not the size of a pull box or a conduit body. The rules in 314.28 are to prevent damage to the conductors when pulled through the conduit body or box. You are correct that 314,28(A)(3) applies to conduit bodies and gives specific permission for sizes boxes and conduit bodies that are smaller than required by (A)(1) and (A)(2), however this permission to use a smaller conduit body only applies to the number of conductors that the "conduit body has been listed for and is permanently marked with the maximum number and maximum size of conductors permitted".
Don
 
Re: The use of 'LB's

Most times an LB of the same size as the raceway (conduit) will not handle the the same conductor fill. When this becomes an issue you need to upsize the LB. Using the next larger LB with reducing bushings will usually do it.

-Hal
 
Re: The use of 'LB's

Don,

Please tell me what this means if you are only permitted to install the amount and size listed on the conduit body? This below is the permission.
...permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill...
Click to expand...
If not, how would you calculate the proper fill for conduit body?
Do conduit bodies come with manufacturers installation instructions and all of the possible fill combinations?

Again, an "LB" would have to be "six times the metric designator (trade size) of the largest raceway". That means 18" for a 3" raceway!

How about a "C Condelet"(straight through)? It would have to be (eight times the metric designator (trade size) of the largest raceway) 24" long for a 3" raceway!


Peter,
The wording under the 314.28 heading is pretty clear that it includes conduit bodies.
Click to expand...
Did you read (A)(1),(2)and(B) and find the words "conduit bodies"? Do you also think "(D) Permanent Barriers" applies to conduit bodies also?
 
Re: The use of 'LB's

You need to comply with bending raduis in coduit bodies, IMO. If you have an Appleton catalog handy, take a look at their mogul LB's. There is a lot of information there on bending radius and how to determine the correnct size LB.
 
Re: The use of 'LB's

Originally posted by websparky:
Peter,
Did you read (A)(1),(2)and(B) and find the words "conduit bodies"? Do you also think "(D) Permanent Barriers" applies to conduit bodies also?
Click to expand...
314.28 (A)(2) Exception
 
Re: The use of 'LB's

Dave,
Please tell me what this means if you are only permitted to install the amount and size listed on the conduit body? This below is the permission.

quote:
...permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill...
Click to expand...
You have to read the complete rule, not just the part you are quoting. The wording from the quote that you are using continues with the word "provided". This places conditions on the phrase that you have quoted. The rest of the section and the restrictions or conditions are shown below.
... provided the box or conduit body has been listed for and is permanently marked with the maximum number and maximum size of conductors permitted.
Click to expand...
If the size and number of conductors being installed in the conduit body satisfies both parts of (A)(3), then the fitting size is not required to comply with (A)(1) or (A)(2). If the size and numbers of conductors being installed do not comply with the permission given in (A)(3) then (A)(1) and (A)(2) apply.
314.28(A)(3) acts as an exception to (A)(1) and (A)(2).
Do conduit bodies come with manufacturers installation instructions and all of the possible fill combinations?
Click to expand...
Yes, in many cases they do come with this information and if not you can get it from the catalogs or factory reps. Here is one such listing.
Don
 
Re: The use of 'LB's

There is a lot of reading in these various subsections.

"314.28(A)(3) Smaller Dimensions. Boxes or conduit bodies of dimensions less than those required in 314.28(A)(1) and (A)(2()"...

This language right out of the NEC makes mention of (A)(1)&(2).


The problem in most instances is one will not be able to conform to these requirements, as most conduit bodies are too small.

After reading this part of the NEC, I agree with what Don has mentioned. It is so very important to continue to read, even if we think we have found our answer in the first sentence or so.

If a conduit body states a maximum number and size of conductor(s), I do not see how we can use larger, even if the cubic inches would permit this for a box.

Pierre
 
Re: The use of 'LB's

Originally posted by websparky:
Don,

When is the last time you saw an LB sized to (B)?

(A)(1),(2)and(B) are addressing "boxes" not "conduit bodies".

(A)(3) and (C) are addressing "conduit bodies".

Chapter 9 Table Notes for Table 1:
(6) For combinations of conductors of different sizes, use Table 5 and Table 5A for dimensions of conductors and Table 4 for the applicable conduit or tubing dimensions.

Area of 4 250kcmil and 1 2/0 ground.
Area x 4 = Total + Area = Total with ground.
256.1 x 4 = 904.4 + 143.4 = 1047.8

Area of 3 400kcmil = 1134.9
Click to expand...
 
Re: The use of 'LB's

Originally posted by warrenwaldrop:
Originally posted by websparky:
You are right that you are wrong!

.....permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill....
Click to expand...
You would be allowed 1200kcmil TOTAL.
Click to expand...
Click to expand...
Okay, if I am allowed 1200Kcmil, then am I limited to the maximum of three conductors?
 
Re: The use of 'LB's

Originally posted by don_resqcapt19:
warrenwaldrop,
Did you have a comment???
Don
Click to expand...
Yes, sorry for sending a blank response.
I think I understand that you say that an LB as indicated could hold up to 1200Kcmil of conductor(s). In 314.28(A)(3) it seems to indicate that the maximum number of conductors can only be as marked on the interior of the LB, which as I stated previously is three. So based on your response then the quantity of conductors really does not matter?
 
Re: The use of 'LB's

warrenwaldrop,
I think I understand that you say that an LB as indicated could hold up to 1200Kcmil of conductor(s).
Click to expand...
No, that was Dave's statement. I do not agree. If the size and number of wires is not shown on the conduit body, then you must comply with 314.28(A)(1) or (A)(2).
Don
 
Re: The use of 'LB's

If the size and number of wires is not shown on the conduit body, then you must comply with 314.28(A)(1) or (A)(2).
Don
Click to expand...
Don,
How does complying with these code references above answer the question of "how many" of different size conductors are allowed?

What is your answer and how did you come by it?
 
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