Why did this fail????????

[don_resqcapt19]

I did not talk about multiconductor cables, but single conductors. You did not answer that question.

I read the word "cables" as some type of multiconductor assembly. What LB are we talking about? If it is marked for 3, 350kcmil, then you can install 3 350kcmil conductors. The rule in the section of the code we are talking about does not apply to installations of over 600 volts.

The question concerned an LB didn't it? Or did other tangential information came into play? I did not read EVERY single post.

There is not tangential info in my post. The rules of the sizing of an LB are the same as for a pull box. The conduit entries must be 6 times the trade size of the conduit apart. If they are not, and the conductors you are installing are #4 or larger, you can only use the size and quantity of conductors that is marked on the fitting itself. The conduit fill tables have nothing to do with the size of conductors larger than #4 that are permitted to be installed in a conduit body.

 

[jusme123]

LB's

LB's

I have run into this years ago and failed. One of the other reason for failing is that the LB may be rated for a max. conductor size.
I have used 4" LB on 3" conduit run for "Bend Radius Compliance."
to the guys that are using the big j boxs as LB I love it. I will be doing that myself. So much easier to pull wire and looks nice to. Just remember to ID the neutral.

take a look at 314.28(A)(2)EX. and table 312.6(A) col 1

 

[don_resqcapt19]

take a look at 314.28(A)(2)EX. and table 312.6(A) col 1

The exception you are citing does not change the rule that says the spacing between the conduit entries must be 6 times the trade size of the conduit for angle pulls. Standard LB conduit bodies do not have that spacing between the conduit entries. The rule that you need to look at is 314.28(A)(3) and if you want to install wires larger that what is marked on the fitting, then you need to find a fitting that complies with the 6x rule.

 

[Ranch]

Sorry for the interuption - to any moderator - when I see a subject such as this and my inquiry is related but not specific, please advise best action. Thanks

Ranch here - need some NEC help

What if anything restricts the pull through an "LB" to 3 conductors and not 4? (3P/4W circuit) Consider non metallic conduit - thanks

 

[Ranch]

What if anything restricts the pull through an "LB" to 3 conductors and not 4? (3P/4W circuit) Consider non metallic conduit - thanks

And base the response on the presumption we can use as large an "LB" as needed

give me some ideas on the 100 - 300kW range for example

Thanks

 

[don_resqcapt19]

Sorry for the interuption - to any moderator - when I see a subject such as this and my inquiry is related but not specific, please advise best action. Thanks

Ranch here - need some NEC help

What if anything restricts the pull through an "LB" to 3 conductors and not 4? (3P/4W circuit) Consider non metallic conduit - thanks

Assuming an LB that is large enough to have the 6x conduit spacing there is no restriction. However most LBs do not have that spacing and you are limited to the maximum size and number of conductors that is marked on the LB. There is no provision in the code rule that lets you convert 3 conductors of one size to 4 conductors of a smaller size.

 

[weressl]

Weressl i'm not taking sides on this but the example of (3) 350 kcmil 5 KV cables in a standard LB listed for (3) 350 conductors is not practical. The jam ratio comes in at 2.94 (2.8-3.2) and the LB would not allow for the bending radius of the cables.

Of course is not practical, but the LITERAL interpretation does not prohibit it. I used this to illustrate the silliness of the base argument which argued that only 3 conductors can be installed in the subject fitting because that is what is marked on the fitting. I maintain that from the mechanical standpoint equivalent cross sectional area conductors can be installed in the fitting, observing the fill rules. Of course we insulation thickness differs between different types so it would be more useful if the conduit fittings are listed with cross sectional fill limitation, the volume fill information with a table for ALL fittings how much fill a termination takes. Bending radius issues with directional change would be a separate issue to be addressed.

 

[don_resqcapt19]

Of course is not practical, but the LITERAL interpretation does not prohibit it.

The code section that we are talking about does not apply to the 15kV cable. The sizing rules for pull and junction boxes used with conductors over 600 volts are found in 314.71. Yes, I know it does not specify conduit bodies in that section, and am not sure where the code addrersss conduit bodies for over 600 volts but you would have to comply with the bending radius rule in 300.34.

I used this to illustrate the silliness of the base argument which argued that only 3 conductors can be installed in the subject fitting because that is what is marked on the fitting. I maintain that from the mechanical standpoint equivalent cross sectional area conductors can be installed in the fitting, observing the fill rules. Of course we insulation thickness differs between different types so it would be more useful if the conduit fittings are listed with cross sectional fill limitation, the volume fill information with a table for ALL fittings how much fill a termination takes.

What fill rules are you talking about? The conduit fill rules have nothing to do with the number of wires permitted to be installed in a conduit body that does not have the spacing that is required by 314.28(A)(1) or (2).

There is nothing in the code that says you can use the equivalent cross sectional area for the purpose of installing more conductors than what is marked on the fitting. The rule in 314.28(A)(3) acts as an exception to the 6x conduit spacing rule that is in 314.28(A)(2). The rule is very specific in stating that you can use a conduit body with a conduit spacing less than 6 times the trade size of the conduit and with conductors #4 and larger only when the fitting is marked with "The maximum number and maximum size of conductors permitted". There is nothing in the code to even suggest that some sort of field calculation can be done to increase the number of conductors that are permitted in the conduit body.

Bending radius issues with directional change would be a separate issue to be addressed.

The bending of the conductor while it is being installed is the very reason for the 6 x conduit spacing rule.

 

[weressl]

The code section that we are talking about does not apply to the 15kV cable. The sizing rules for pull and junction boxes used with conductors over 600 volts are found in 314.71. Yes, I know it does not specify conduit bodies in that section, and am not sure where the code addrersss conduit bodies for over 600 volts but you would have to comply with the bending radius rule in 300.34.

What fill rules are you talking about? The conduit fill rules have nothing to do with the number of wires permitted to be installed in a conduit body that does not have the spacing that is required by 314.28(A)(1) or (2).

There is nothing in the code that says you can use the equivalent cross sectional area for the purpose of installing more conductors than what is marked on the fitting. The rule in 314.28(A)(3) acts as an exception to the 6x conduit spacing rule that is in 314.28(A)(2). The rule is very specific in stating that you can use a conduit body with a conduit spacing less than 6 times the trade size of the conduit and with conductors #4 and larger only when the fitting is marked with "The maximum number and maximum size of conductors permitted". There is nothing in the code to even suggest that some sort of field calculation can be done to increase the number of conductors that are permitted in the conduit body.

The bending of the conductor while it is being installed is the very reason for the 6 x conduit spacing rule.

If you read carefuly what I wrote, you can perhaps avoid attributing statements to me that I did not make.

 

[LarryFine]

If they are not, and the conductors you are installing are #4 or larger, you can only use the size and quantity of conductors that is marked on the fitting itself.

I maintain that from the mechanical standpoint equivalent cross sectional area conductors can be installed in the fitting, observing the fill rules.

There is nothing in the code that says you can use the equivalent cross sectional area for the purpose of installing more conductors than what is marked on the fitting.

There is nothing in the code to even suggest that some sort of field calculation can be done to increase the number of conductors that are permitted in the conduit body.

If the argument that more smaller conductors can be substituted is valid, what about fewer larger conductors? Can we exceed the size label if we go lower than the quantity label? Hmmm.

 

[don_resqcapt19]

If you read carefuly what I wrote, you can perhaps avoid attributing statements to me that I did not make.

I quoted your post.

 

[augie47]

hey guys!
The rest of us learn a lot from your post as you are both highly intelligent and learned. Don't let it deteriorate into a spitting contest, please.

 

[weressl]

If the argument that more smaller conductors can be substituted is valid, what about fewer larger conductors? Can we exceed the size label if we go lower than the quantity label? Hmmm.

As I said from the mechanical standpoint of view that is how the rule SHOULD be established in and by the NEC. What use of establishing a fill rule for a conduit when the accompanying fitting will limit that fill that in practical terms the conduit fill can only be utilized on straight, fitting-less runs?

I was attempting to establish a clear and logical path that addresses all the major issues associated with conduit run fill and bending radius requirements. Alas the existing rules apepar to be put together as a series of afterthoughts where the problems were addressed as they arose and each had to live with the shortcomings of the previous rulings that was all encompassing in their time and place.

 

[augie47]

logic and code ? A oxymoron ??
I don't have the data available, but I wonder if one goes back to my youth and looks at the earlier wiring methods (RHH-RHW) if the conduit fill and the conduit fittings were the same.
Pure conjecture on my part, but perhaps the advent of the "smaller" conductors came after the original fitting design and most folks gave it no thought as "thats what we always used".
From some of the conduit fitting limitations I know of, they seem to be in line with the RHW fill tables.

 

[iwire]

What use of establishing a fill rule for a conduit when the accompanying fitting will limit that fill that in practical terms the conduit fill can only be utilized on straight, fitting-less runs?

I can get a 4 11/16" square box that accepts 1" conduit, does that automatically mean the box can accept any size or number of conductors that the conduit can or do I have to use my head and design my conduit run correctly?

Alas the existing rules apepar to be put together as a series of afterthoughts where the problems were addressed as they arose and each had to live with the shortcomings of the previous rulings that was all encompassing in their time and place.

I agree but will add that for better or worse that is the way of things from the NEC to Federal and state laws.

 

[weressl]

I can get a 4 11/16" square box that accepts 1" conduit, does that automatically mean the box can accept any size or number of conductors that the conduit can or do I have to use my head and design my conduit run correctly?



I agree but will add that for better or worse that is the way of things from the NEC to Federal and state laws.

No argument Bob, I agree.

I'm just sayin'.......

The beauty of logical arrangements are that you don't have to memorize endless number of combinations, once you understand the logical base that's all you need to remember and it is easier to figure out than mis-remembering.

 

[don_resqcapt19]

As I said from the mechanical standpoint of view that is how the rule SHOULD be established in and by the NEC. What use of establishing a fill rule for a conduit when the accompanying fitting will limit that fill that in practical terms the conduit fill can only be utilized on straight, fitting-less runs? ...

That would result in some very large and expensive conduit bodies, if they all had to be suitable for the maximum permitted conduit fill.

 

[weressl]

That would result in some very large and expensive conduit bodies, if they all had to be suitable for the maximum permitted conduit fill.

According to the current paradigm that is correct.

Again; try to follow the logic I presented.

 

[resistance]

hey guys!
The rest of us learn a lot from your post as you are both highly intelligent and learned. Don't let it deteriorate into a spitting contest, please.

I agree!! :smile:

 

[weressl]

How to revitalize the industry? Toolbox teaparty, CHANGE THE CODE!

How to revitalize the industry? Toolbox teaparty, CHANGE THE CODE!

I quoted your post.

Don,

You asked me what fill rules was I talking about?! None. You are talking from the Code's viewpoint, I am reasoning why the Code is not logical or consistent, or why their rules defie common sense due to the historical development of the document. I am only trying to present a scenario how it could be reworked in a conscise fashion.


Simply,

• Deal with fill first and anchor it to the conduit,(eg. fill is determined by the sum of crossectional area of the conductors, regardless of their insulation thickness. I think that the % of available fill area should be consistent, not dependent on the # of conductors)
• deal with fittings second, minimum fill is equivalent to the connecting conduit,
• Increase fitting size when:
  1. terminations or
  2. directional changes required.

Next step would be ampacity. based on the current desity and thermal dissipation ability of the raceway profile and ambient temperature. We have new energy efficiency rules, yet the motor table did not change. Size the cables and overloads to the nameplate!

All these can be built into a small handheld calculator along with other code related formulas and tables on a replaceable chip, so it can be replaced as the Code changes. It would allow the electricians to perform what is called today 'engineering calculations' to use the optimum size equipment ALL the times.

This can revolutionize the trade since with the reduction of material to the optimum needed will enble the industry to spend more money as they get more for the bang, ergo more $ is left for labor. Inspectors work would be simplified and the electricians would greatly improve their installations' accuracy.