Bend space requirements

[MechEdetour]

Would be nice to get into a discussion about bend space requirements for conductors that are brought into enclosures. The NEC has requirements laid out for installations, and obviously relevant standards also have requirements that manufacturers need to comply with when manufacturing equipment (those requirements are typically duplicated tables pulled from the NEC).

I’ve had some pretty interesting conversations with people and how they interpret the requirements. Some of the verbiage seems to direct people to one table or another when stating what the requirements are. We can argue all day about what is better (especially when we get to conductors in the MCM range) when a large conductor is subject to a 90 deg bend within an 8” gutter to exit an enclosure.

But one thing I am after is how does everyone interpret bend space requirements? I have other questions too, but don’t want to write a first post that fills the whole page . . . already know I’ll have a hard time keeping it short.

Also just to address:
- Not bend radius (as related to integrity of the insulation of a conductor), but space required to bend/route conductors.
- Strictly looking for a requirement, not for something that could potentially be more optimal.

NEC 2014

312.6(B)(1) Conductors Not Entering or Leaving Opposite Wall
Table 312.6(A) shall apply where the conductor does not enter or leave the enclosure through the wall opposite its terminal.

Those with the NEC can reference the table, but I will refer to Table 312.6(A) as the “smaller requirement.”

312.6(B)(2) Conductors Entering or Leaving Opposite Wall
Table 312.6(B) shall apply where the conductor does enter or leave the enclosure through the wall opposite its terminal.

I’ll refer to Table 312.6(B) as the “larger requirement.”

Situation “A” is what I see as a representation of a conductor not entering or exiting the opposite wall. The note under table 312.6(A) also states “Bending space at terminals shall be measured in a straight line from the end of the lug or wire connector (in the direction that the wire leaves the terminal) to the wall, barrier, or obstruction.” I have this measurement addressed by dimension “B1” and graphically represented by the yellow arrow to match the verbiage.

The requirement, as I read the NEC and apply the relevant sections for situation “A”, states that dimension “B1” must be 5” for a 300MCM conductor.

Situation “B” is what I see as a representation of a conductor entering or exiting the opposite wall, whether it be “Run 1” or “Run 2.” Note 1 under table 312.6(B) states “Bending space at terminals shall be measured in a straight line from the end of the lug or wire connector in a direction perpendicular to the enclosure wall. I have this measurement addressed by “B2” and graphically represented by the red arrow to once again match verbiage.

The requirement, for this case, states that dimension “B2” must be 10” for a 300MCM conductor.

I’ve referenced several resources such as various UL standards, the NEC handbook, etc. They all bring me back to what I have shown for what is defined as “opposite wall” and which table to apply when exiting different walls.

I’m curious to know how others go through this exercise. I bring this matter up because on a few occasions now, I’ve had people argue that I have the tables backwards, and the “opposite wall” is actually the top of the enclosure. This baffles me considering that if this was true, then the case where you wouldn’t leave the “opposite wall” (top), would then require the use of the other table for the remaining left, right, and bottom walls of the enclosure.

I’m going to leave this here. I actually hope to get into the “why” it is this way, and maybe a bit more into where exactly the dimensions are to be measured from when different terminals come into play. . . but for now what is everyone else’s take?

 

[jusme123]

Table 312.6(A)
On the top of the page just above the title of the table write this:

" Conductors not leaving or entering opposite wall - Gutter Space"


Table 312.6(B)
On the top of the page just above the title of the table write this:
"conductors leaving or entering opposite wall - Straight in"

 

[jusme123]

.......

 

[Pizza]

You make some valid points, but it is very rare I ever think about bending space. Usually the enclosures are big enough and no inspector would ever think to call me on it.


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[MechEdetour]

Table 312.6(A)
On the top of the page just above the title of the table write this:

" Conductors not leaving or entering opposite wall - Gutter Space"


Table 312.6(B)
On the top of the page just above the title of the table write this:
"conductors leaving or entering opposite wall - Straight in"

So I think we're in agreement at this point.

You make some valid points, but it is very rare I ever think about bending space. Usually the enclosures are big enough and no inspector would ever think to call me on it.


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I agree also. However in the instances where it is an issue, it'd be interesting to hear what both parties' arguments are. Where I think it causes some problems, in my opinion, is when certifying bodies misinterpret which table to apply, and then manufacturers build equipment that does not provide the adequate space for terminating field conductors (ie. providing space adequate to leave side walls but not straight out the bottom due to the use of the wrong table).

 

[Pizza]

So I think we're in agreement at this point.



I agree also. However in the instances where it is an issue, it'd be interesting to hear what both parties' arguments are. Where I think it causes some problems, in my opinion, is when certifying bodies misinterpret which table to apply, and then manufacturers build equipment that does not provide the adequate space for terminating field conductors (ie. providing space adequate to leave side walls but not straight out the bottom due to the use of the wrong table).

One example that comes to mind is a meter socket and a 200 amp panel back to back with a nipple in between.
Most of the time you see it where the meter socket is on the outside of a garage and the panel in the inside of the garage.
Technically you can't run 4/0 al. In that situation because the panel depth isn't big enough for bending space requirements but you see it all the time.

 

[Carultch]

One example that comes to mind is a meter socket and a 200 amp panel back to back with a nipple in between.
Most of the time you see it where the meter socket is on the outside of a garage and the panel in the inside of the garage.
Technically you can't run 4/0 al. In that situation because the panel depth isn't big enough for bending space requirements but you see it all the time.

In such an instance, would you get to take any credit on reducing bending space, if you use finely stranded wire (and appropriate termination adaptations, of course)?

 

[Pizza]

In such an instance, would you get to take any credit on reducing bending space, if you use finely stranded wire (and appropriate termination adaptations, of course)?

Just use copper

 

[Carultch]

Just use copper

Which is probably what I'd do in that specific example. But what about the general case of bending space? Does fine stranded wire help you in a close quarters enclosure?

 

[GoldDigger]

Which is probably what I'd do in that specific example. But what about the general case of bending space? Does fine stranded wire help you in a close quarters enclosure?

In practice, yes. By code no.
AHJ discretion, at best.

 

[MechEdetour]

Does anyone know when the deflection of conductors was first introduced into the NEC? I'd like to see how it looked when it was introduced and how it evolved if at all.

 

[kwired]

You make some valid points, but it is very rare I ever think about bending space. Usually the enclosures are big enough and no inspector would ever think to call me on it.


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What you might run into though is a 200 amp main breaker panel that has lugs that accept 300kcmil conductors but bending space is only sufficient for 250 kcmil max.

One example that comes to mind is a meter socket and a 200 amp panel back to back with a nipple in between.
Most of the time you see it where the meter socket is on the outside of a garage and the panel in the inside of the garage.
Technically you can't run 4/0 al. In that situation because the panel depth isn't big enough for bending space requirements but you see it all the time.

I don't agree with that. Conduit bodies have less depth then the panel many times, it is more about where the entry is in relation to the termination. There is no rule on minimum bending radius of a conductor, there is bending space requirements at terminations though.