Sizing Gutters?

[tedge]

Does anyone out there have a graphic that explains gutter sizing? Article 366 refers you to Table 312.6(A), but I can't make heads or tails of what I'm looking at there. I do mostly resi work and I'm venturing into commercial, so I've never had the need to size a gutter to maximize space and minimize cost. Any help would be appreciated.

EDIT: A little more info might be helpful I suppose. I want to tap into an existing 3-phase 400A feeder. I want to add a gutter in the existing 4" PVC conduit that is big enough for me to tap into the 2 250KCMIL/phase with a #3/phase. These tap conductors would drop directly into a 100A fused disconnect to feed a new sub-panel. I guess another question would be, can I tap only 1 of the conductors/phase, or do I need to tap each of the paralleled conductors.

 

[raider1]

Here is a Mike Holt graphic that helps explaine gutter sizing.

Chris

 

[augie47]

although, it does not have impact on your particularb job, also keep i mind the limitations of 376.22 in that therre is a 20% fill limit, and derating also applies after 30 current-carrying conductors. Also,, if the wireway is used as a pull box Art 314 applies.

More directly to your "job", I don't beleive the plan would be Code compliant. IMHO, you you need to tap both phases and your parallel taps would have to be 1/0.

 

[raider1]

IMHO, you you need to tap both phases and your parallel taps would have to be 1/0.

I agree.

Chris

 

[acrwc10]

as far as your parallel conductors goes I would terminate them into a distribution block then come out of the block with your tap conductors.

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[iwire]

as far as your parallel conductors goes I would terminate them into a distribution block then come out of the block with your tap conductors.

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Don't forget to order a cover with that block, the NEC prohibits live exposed parts in wireways

 

[raider1]

Here is a Mike Holt graphic that helps explaine gutter sizing.

Chris

I fixed the image, sorry.

Chris

 

[tkb]

Can you connect the parallels together on the block and tap with a single conductor?

 

[tedge]

OK, so IF I have parallelled tap conductors, they have to be 1/0. But TKB raises the question, if I terminate both phase conductors (2 cond./phase)to one of the terminal blocks shown above, couldn't I then run one wire as my tap conductor keeping it at #3 for 100A? Or am I not allowed to terminate them all onto one block? Seems like the best way to keep them all "the same" length. That would certainly cut down on the clutter in the gutter.

 

[augie47]

One of the many great things about the Forum is the variety of good ideas.
Using the block would allow you to use one tap condcutor. You haven;t mentioned length, so be sure to comply wth 240.21

 

[infinity]

OK, so IF I have parallelled tap conductors, they have to be 1/0. But TKB raises the question, if I terminate both phase conductors (2 cond./phase)to one of the terminal blocks shown above, couldn't I then run one wire as my tap conductor keeping it at #3 for 100A? Or am I not allowed to terminate them all onto one block? Seems like the best way to keep them all "the same" length. That would certainly cut down on the clutter in the gutter.

If you're tapping one #3 to the feeder that's protected at 400 amps you'll need to comply with the 10' tap rule, 240.21(B)(1). If you can't then your tap conductors will need to comply with the 25' tap rule which requires a tap conductor ampacity set at a minimum of 1/3 the ampacity of the 400 amp feeder 240.21(B)(2).

 

[tedge]

The OCP on the existing 3-phase feeder is a 400A circuit breaker. Each phase consisits of (2) 250 kcmil copper THHN. My new gutter and taps would be outside the building and less than 10' to a fused 100A disconnect.

If I'm reading it right, 240.21(B)(5) allows me to use any length tap with no ampacity adjustments to the taps themselves in this scenario.

75 degree column of 310.16 says #3 copper is good for 100A. I'd be using THHN.

Am I missing something?

 

[infinity]

The OCP on the existing 3-phase feeder is a 400A circuit breaker. Each phase consisits of (2) 250 kcmil copper THHN. My new gutter and taps would be outside the building and less than 10' to a fused 100A disconnect.

If I'm reading it right, 240.21(B)(5) allows me to use any length tap with no ampacity adjustments to the taps themselves in this scenario.

75 degree column of 310.16 says #3 copper is good for 100A. I'd be using THHN.

Am I missing something?

Nope, sounds like you've got it. What was missing were the words "outside the building" from you previous posts.
As you've mentioned outside the building has different tap rules regarding length (unlimited). No THHN however.

 

[acrwc10]

OK, so IF I have parallelled tap conductors, they have to be 1/0. But TKB raises the question, if I terminate both phase conductors (2 cond./phase)to one of the terminal blocks shown above, couldn't I then run one wire as my tap conductor keeping it at #3 for 100A? Or am I not allowed to terminate them all onto one block? Seems like the best way to keep them all "the same" length. That would certainly cut down on the clutter in the gutter.

The blocks come in many differing configurations, that would allow you to bring your larger paralleled feeder/service conductors into one side of the block thus meeting the requirement of 310.4(A)
Then coming off the other side of the block you can run single feeder to each disconnect or what ever it is you are going to. This makes for a really clean installation.

 

[tedge]

Yes, THWN it is. Thanks for the replies.

Anyone have a link to the distribution block catalog page? It looks like a Buss product maybe?

 

[tedge]

Another question: As Augie47 pointed out, if this gutter was considered a pull box, I'd have to comply w/ Art. 314. So, I want to cut a 4" PVC conduit to add my gutter. The 4" PVC will enter and exit the gutter directly across from one another. Could this be considered a straight pull box even though the conductors are bent over into the gutter and tapped?

 

[raider1]

Another question: As Augie47 pointed out, if this gutter was considered a pull box, I'd have to comply w/ Art. 314. So, I want to cut a 4" PVC conduit to add my gutter. The 4" PVC will enter and exit the gutter directly across from one another. Could this be considered a straight pull box even though the conductors are bent over into the gutter and tapped?

Take a look at 376.23(B).

Chris

 

[tedge]

376.23(B) would be what I should comply with IF this would be considered a pull box. I'm not pulling wires through it per se, but the conduit entries will be directly opposite each other. Would this be a pull box?

 

[raider1]

376.23(B) would be what I should comply with IF this would be considered a pull box. I'm not pulling wires through it per se, but the conduit entries will be directly opposite each other. Would this be a pull box?

I would say yes, what you have is a pull box.

Here is what that section says:

(B) Metallic Wireways Used as Pull Boxes. Where insulated conductors 4 AWG or larger are pulled through a wireway, the distance between raceway and cable entries enclosing the same conductor shall not be less than that required by 314.28(A)(1) for straight pulls and 314.28(A)(2) for angle pulls. When transposing cable size into raceway size, the minimum metric designator (trade size) raceway required for the number and size of conductors in the cable shall be used.

Chris

 

[tedge]

Damn. That means I'd need a 32" wide gutter. Hmmm. No disrespect Raider1, but I'd like to hear what others think on this. Gutters are made to have multiple conduit entries in the top, bottom, etc. I'm having trouble envisioning how they could be used as anything but a pull box by your interpretation. Yet we see them used in similar ways pretty often.

Maybe my plan is screwed by having a 4" conduit entry.