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#191505 - 12/31/09 02:24 PM Auxiliary Gutter Sizing
Webmaster Offline

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Registered: 10/07/00
Posts: 3142
Loc: NY, USA
Quote:
This auxiliary gutter used as a pull box is 5ft long, 14inches deep by 14inches in height. There are two 4inch conduits feeding the bottom of the gutter with 4x600MCM conductors in parallel in each which pass straight through to the two 4inch nipples which connect to the bottom of the meter assembly feeding the 800 amp breaker. Is this gutter properly sized?

shortcircuit


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#191506 - 12/31/09 03:27 PM Re: Auxiliary Gutter Sizing [Re: Webmaster]
renosteinke Offline
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Registered: 01/22/05
Posts: 5299
Loc: Blue Collar Country
Let's look at this as an exercise, for the benefit of those who have never actually 'sized' things.

In choosing a gutter, we have a couple of different criterial to meet. Not only does there need to be room for wires (cable fill), there has to be adequate bending space, and there is a limit to the number of circuits in any particular cross section. Exactly how you count the wires matters, as a spliced wire counts as two for cable fill, but not for the circuit count.

You say that the wires pass 'straight through,' so I will assume there are no splices. I will also assume that the GEC passes through the raceway.

First, the cross sectional rules: For the 4" conduits, I will assume each contains 4 copper wires, 600MCM, and the insulatiion is THWN. Table C8 tells me that 4"RMC has space for as many as six, so we're OK there.

Now .. do we have an 'auxilliary gutter"(Atricle 366), or a 'pull or junction box"(Article 314)? From the tables in 314.16, I think it's safe to assume that this section is aimed at much smaller boxes, and that Article 366 is where we need to look for guidance.

Lest there be any doubt, Article 366 begins it's definition with "enclosure used to suppliment wiring space at meter centers ..."

366.22 limits our wires to 20% of the cross sectional area of the box. Table 5 gives us an area for each 600MCM wire as 0.8676 sq. in. Since, in addition to the circuit wires, we also have a GEC and bonding jumpers in this gutter, we'll just assume 10 wires for the sake of simplicity. 10 x 0.8676 = 8.676 sq. inches. Five times that (20% rule) tells us that the minimum cross-sectional area is 43.38 sq. in. You gave the size of the gutter as 14x14", or 196 sq. in ..... so there's plenty of space.

Let's look at bending space. 366.58(B) tells us that where used as a pull box, we need to look at 314.28(A) -pull box rules - for the size of the box.

314.28(A) takes us away from wire size, and focuses on the 4" conduit used. For straight pulls, we are told the length has to be 8x the nominal pipe sixe ... 8x4" in this case ... or 32", if we consider these to be 'straight' pulls. If we consider them 'angle' pulls - and a case can be made, as the pulls are not absolutely straight - we need to look at both of the pipe runs. That is, the math is 4 (pipe sixe) x 6 (multiplier) + 4(2nd pipe size). This comes to 28".

Let's back up again, and see where we might 'cheat.' Code would have allowed us to use 3-1/2 pipe. 314.28(A) also says that the distance will not be less thn 6x the pipe size, no matter what assumptions you make. 3-1/2 x 6 = 21.

In other words, no matter how you slice it, we need 21" between the two conduit entries. The gutter is two small.

Let's look at the argument that you have a 60" gutter, so you can make the wire 'fold' in. This still gives us a need for 21" for the necessary right-angle and "U" bends, so again, the gutter is too small.

If the pipe entries were truly more-or-less in line, and the gutter simply used to adjust for minor differences between the pipe and the KO locations, I'd be willing to let it pass. There's enough offset, though, that I can't really say that you're 'pulling through' the gutter. That would be one ugly pull! I'd almost have to use single right-angle bends, and splice the wires at the far end of the gutter. The gutter, or box, however you slice it, needs to be 21" tall, or 50% larger than it is.

Please note that at no point did we look at the 'minimum bending radius' of the wire. That's really not relevant here, as we are passing through the enclosure, not making connections within it.

If I were the guy on the job .... sometimes life gives you lemons. I'd try to get approval, as I see there are real problems on the site with clearances. Then I'd make a serious note to not let this happen again!

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#191540 - 01/01/10 03:25 PM Re: Auxiliary Gutter Sizing [Re: renosteinke]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
Everything looks too low versus final grade.

The underground conduits should have been re-dug and shifted. That would take less labor than this eye-sore.

If I were the GC I'd reject the work.

What's with the LB's? If the entire assembly were raised everything would start to make sense.

It's as if two different foremen schemed up this array.

The wasted materials and labor indicates foreman #2 flunked out of class.
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Tesla

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#191542 - 01/01/10 03:55 PM Re: Auxiliary Gutter Sizing [Re: Tesla]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5299
Loc: Blue Collar Country
You know, Tesla, you might be spot-on. I had not looked at the installation as a whole, but the waterproofing on the concrete does suggest that the grade was intended to be higher.

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#191550 - 01/01/10 06:32 PM Re: Auxiliary Gutter Sizing [Re: renosteinke]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
I suppose they have to be that low so the meter reader can read the top meter. I wonder if they just couldn't afford the last 18" of dirt?
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Greg Fretwell

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#191553 - 01/01/10 07:01 PM Re: Auxiliary Gutter Sizing [Re: gfretwell]
frenchelectrican Offline

Member

Registered: 02/06/03
Posts: 938
Loc: Wi/ Paris France { France for ...
IMHO .,,

They did bloody poor job on the whole thing .,,

• the whole meter stack is too low
• the service entrance conduit is out of whack
• wrong gutter size.

I did count the number of rows of prefourm blocks and they are typically 8 by 16 inches and with waterproof tarring the whole thing need to be rasied couple feet up.

Merci,Marc
_________________________
Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)


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#191555 - 01/01/10 07:15 PM Re: Auxiliary Gutter Sizing [Re: frenchelectrican]
leland Offline
Member

Registered: 08/20/07
Posts: 856
Loc: Lowell area, Ma. USA
Ugly yes,the gutter looks as if only 12" under the main (caved in).
Did they use hubs on the top? I can't zoom in to tell.

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#191556 - 01/01/10 07:21 PM Re: Auxiliary Gutter Sizing [Re: leland]
frenchelectrican Offline

Member

Registered: 02/06/03
Posts: 938
Loc: Wi/ Paris France { France for ...
Leland .,

If they used Meyers hub IMO it too tight to get corret spacing there unless they use the overhead hub with flange which I doubt with this type of metering stack.

Merci,Marc
_________________________
Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)


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#191558 - 01/01/10 07:44 PM Re: Auxiliary Gutter Sizing [Re: frenchelectrican]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5299
Loc: Blue Collar Country
The gutter is attached to the disconnect cabilet using rigid couplings and chase nipples on either end.

That close to the upper cabinets, I would not insist on a Myers' hub ... I'd call it a 'damp' location there.

PoCo's usually want the center of the meter face no more than 6-1/2 ft from grade.

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#191560 - 01/01/10 08:55 PM Re: Auxiliary Gutter Sizing [Re: Webmaster]
shortcircuit Offline
Member

Registered: 06/27/04
Posts: 608
Loc: massachusetts
Thankyou Reno for the effort to explain the proper way to size this Auxiliary Gutter. I believe also the gutter was used because the underground conduits didn't line up with the main 800amp cabinet. So if the proper sized gutter (32inch in height)were used the upper disconnects in the meter stack modules would be over the 6ft 7inch rule.

The grade is as shown in the photo. The wall was sealed above grade.

The LB's exiting the top of the meter modules are connected with myers hubs. These LB's enclose the 3/0 feeder conductors to the tennant units. Only 4 of the 8 positions have been installed.

The smaller LB connected to the center 800amp main encloses the 3/0 grounding electrode conductor. This also uses a myers hub.

The gutter does connect to the bottom of the 800amp cabinet with couplings and chase nipples. No bonding of these 2 nipples or the gutter are present. The two 4inch conduits at the bottom of the gutter are connected in a poor workmanship manner (angled with locknuts improperly seated) but effort was made to bond these conduits with a 1/0 conductor in series through bonding bushings.

Furthermore the ferrous conduit to the grounding electrode is not continous from cabinet to electrode or bonded at all. Also the concrete encased electrode present at the site is not part of the electrode system.

Code sections violated include: 110.12, 230.7, 250.64(E), 250.92, 250.94, 250.102(C), 300.7(A), 366.58(B)

The CH equipment is listed for top exit with the Myers Hubs. But think of what will happen if and when they do leak water.

shortcircuit

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