4/0 cable into the back of a 3 1/2 inch deep panel

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Re: 4/0 cable into the back of a 3 1/2 inch deep panel

I jumped a few pages but if you use a service loop a less acute angle into the panel and a circle back around,yes it takes up space but not enough i do that with AL SER.And bending radius is OK
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Alan Manche is a very intelligent person and well respected in our industry. As a side note to this, I have attended quite a few of the national seminars and the disputes that occur there between individuals is not much different than the interesting ones we have here :) ), I think that UL requirements and NEC do not always match each other in their intent, and for field installers as opposed to factory installers we need to focus on the NEC.
It is my understanding that UL 83 wire bending radius is for factory installed bending radius (which is under more control and performed with machines) and tested by the manufacturer at the factory. I am sure you can recall some manufactured equipment with factory bends that are 90 degree angles ;) , so one does not measure the depth of the enclosure, but the distance from the back of the enclosure to the lugs.

Think about this: when you are wearing a long sleeved shirt and you bend your elbow, you can feel the pressure it exerts on the sleeve. Now picture in your mind how this will affect the insulation on the back of one of those sharp bends.

Pierre
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

A 90 degree bend in a wire is a soft or easy bend in a wire, its the radius value that you apply that is critical.

A example would be bending a piece of 4/0 wire the size of a hula hoop ,its quadrants would have about a 18" radius.

bend the same piece of 4/0 around a coffee can and the quadrants would have about a 3" radius.....

same 90 degree bends............different radius values.

John
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Originally posted by pierre:
BTW - The bending radius in 312.6(A) is to the lugs, not to the panel cover ;) , so one does not measure the depth of the enclosure, but the distance from the back of the enclosure to the lugs.
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314.28(A)(2) Angle or U Pulls. Where splices or where angle or U pulls are made, the distance between each raceway entry inside the box and the opposite wall of the box shall not be less than six times the metric designator (trade size) of the largest raceway in a row. This distance shall be increased for additional entries by the amount of the sum of the diameters of all other raceway entries in the same row on the same wall of the box. Each row shall be calculated individually, and the single row that provides the maximum distance shall be used.

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).
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So I am not sure if we have to measure from the back to the lugs or from the back to the front.

As has been pointed out you could make the bend like a ? to use up the full depth of the enclosure.

This is of course that the straight line distance from the terminals to the sides or top is still in compliance.
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Bob
I do not think for this specific type of installation you can use the section on U or angle pulls as a reference, as that is for junction boxes and conduit bodies.

The references to 408.35 do not pertain to the entrance of conductors from the back of an enclosure, but from the top, side and bottom.
312.6(A) specifically addresses this type of installation and I do not see any other way around it. Read 408.35 exception 3 very carefully.

Pierre

[ March 09, 2004, 06:15 AM: Message edited by: pierre ]
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

i wire so it seems now thast you do agree that 3126a refers to a straight line from the terminal to the top and 3126b refers to a distance from the lug or terminal to the side eh? if so where is your reference regarding anything to the back of the can excepting maybe ul 83? with the space that the manufacturers give from that openeing to the lug an fairly soft radius is obtained even though a 90 is eventually made its is a soft radius 90 mehtinks.
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Maybe I am being to simplistic.

Bending space is required in whatever direction the wire is bent. It makes no difference if it is forward, backward, up, or down.

If the conductor is installed basically in a parallel line (opposite to point of entry) wire bending space is required for two offset bends.

If the conductor is install at an angle, then space for one bend is required.

Can someone explain why this simplistic view can not be used to interpret all of the "wire bending space" requirements in the NEC including, 408.35, 408.10, 312.6, 312.11(c), and 314.28
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Originally posted by stew:
i wire so it seems now thast you do agree that 3126a refers to a straight line from the terminal to the top and 3126b refers to a distance from the lug or terminal to the side eh?
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No that is not what I think, what I think is those tables apply like you say and 312.6(A) will apply to the distance from the front to the back.

You need enough space in both directions.

Originally posted by pierre:
Bob
I do not think for this specific type of installation you can use the section on U or angle pulls as a reference, as that is for junction boxes and conduit bodies.
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I see no reason if that applies to junction boxes and conduit bodies that it would not apply to all situations that have a removable cover opposite the entrance of the conductors.

As Jim D. has put so clearly

Bending space is required in whatever direction the wire is bent. It makes no difference if it is forward, backward, up, or down.
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I see no reason a panel enclosure is any less of a "box" than a splice can, gutter, pull box, conduit body etc.
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Looks to me like we need to go to the code writing panel and pick their brains to see what they meant when they wrote that section eh?
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Iwire, Am I missing something or what? ..... I was an electrical contractor back in the late 60's and wired lots of residences the excact same way it is done today. It is hard to believe that after 35 years, the 3.5" panelboard is suddenly not meeting code using the exact same service entrance wires....... Are all of the inspectors ignorant of this "apparent" problem, or to them it never was a problem and still isn't. :)
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

I meant to ask anyone, if they have ever had a problem with an inspector rejecting the service entrance with a 3.5" panel and 4/0? :)
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Jibber seeing as I have been such a loud mouth on this thread :D

But I have never seen anyone get shot down for not derating conductors in raceways even though that is very often violated.

Does that mean the rule does not exist?
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Originally posted by iwire:
But I have never seen anyone get shot down for not derating conductors in raceways even though that is very often violated.

Does that mean the rule does not exist?
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Bob: Why don't you ask the electrician on the job I inspected today that question?....
....I'll bet he won't take it very well. :D
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Originally posted by ryan_618:
Bob: Why don't you ask the electrician on the job I inspected today that question?....
....I'll bet he won't take it very well. :(
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Re: 4/0 cable into the back of a 3 1/2 inch deep panel

It against code, not enough bending space. The required space is anywhere in the panel, not just at the lugs.
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Jibber
I went back to '71 code book and the same requirement is there, but the wording is slightly different. If an inspector passes an installation, he himself may not be aware of the requirement. This does not absolve the contractor from reprisal if something goes wrong.

Pierre
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Ryan, , Do you really think that this age old wiring of the service entrance has ever caused any genuine documented problems as a result from coming into the rear of a 3.5" panel with a 4/0?

It seems to me that by now, somewhere in the USA an inspector would have shot them down on that, and the word would have spread or have been appealed and corrected. I think that most inspectors have been applying common sense.

Is there a conflict in the NEC, or it it a real safety issue. The reason that 8' fluorescent light bulbs need not be covered is because there hasn't been many cases of someone being hurt by them breaking. Seems to me the reasoning should be the same here. Make safety codes to correct problems.
 
Re: 4/0 cable into the back of a 3 1/2 inch deep panel

Pierre, Are you aware of any problems that have been caused by this subject? ;)
 
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