Auxiliary Service Gutter sizing ?

[BlueFox]

After spending a considerable amount of time reading the 2011 NEC I still could use some help on sizing a sheet metal auxiliary gutter on a 350amp single phase 120/240 residential service.

Heres the proposed layout:

Overhead service 350 kcmil (as per Table 310.15(B)7 installed in a 3? rigid riser into the top of the meter can. The service disconnecting means will consist of two panels, one 200amp and one 150amp both with main breakers. One feed through panel to supply a barn through an underground feeder.

Coming out the bottom of the meter can with a 3? rigid nipple going down to an auxiliary gutter directly below the meter can. (Hopefully I can use sealing lock-nuts instead of a meyers hub in the top of the gutter). Is it ok to use sealing lock-nuts here.

After tapping onto the 350 using polaris taps was planning on leaving the gutter to the left with a 2? nipple with 3/0 copper to feed the 200amp panel in the ko' provided in the panel., and leaving the aux gutter to the right with 3/0 copper as well (just to keep things simple) to feed the 150amp panel.

This is what I figured so far looking at article 366.22 and 376.22
To allow for some extra room I figured the wire size at 500kcm for the 20% fill
for 500kcm THHN the area is 0.7073 X 3 = 2.121?
for 3/0 THHN the area is 0.2679 x 6 = 1.607
Total = 3.7293 divided by 20% = 18.65?

Don't know how much room to allow for the taps. Are polaris taps considered terminals and need to a
According to 366.58 I need to use Table 312.6(A) for width of the gutter.

The 350kcm will be going straight down inside the gutter and terminate in a polaris tap then the 3/0 conductors will come out of the tap to feed the respective panels.
The ahj inspector said to connect the GEC to the grounded conductor (neutral) in the gutter, so the tap would have four conductors on the terminal and the other terminals will have three conductors.

According to the table in 312.6(A) for width requirements it looks like for terminals with four wires sized 300-350kcm needs to be 10 inches. And those for three wires need to be 8 inches.

Have some ideas about the sizing of the gutter however since this is the first time to size one I sure could use some help.

 

[John120/240]

I'm confused:?:? Why do you need a gutter ? A 400 A meter can (320

continous) has enough room to just use 2 barrel lugs on each phase.

Exit the meter with conduit or LB, whatever suits your fancy.

 

[BlueFox]

Thats what I thought at first however the ahj was considering it parallel feeders if i used double lugs and said I could not run parallel feeders to two different locations.

 

[BlueFox]

parallel feeder

parallel feeder

the ahj said it would be considered parallel feeders and I could not use double barrel lugs and terminate at two different locations.:weeping:

 

[John120/240]

BlueFox has me confused as to his situation.:? Here we are allowed 10 ft of

service cable before the first means of disconnect. So install the panels side by

side on the inside wall. Yes I do need to read up on tap rules. So what is

the advantage to use a gutter ?

 

[BlueFox]

I really don't see an advantage at all. It seems like adding a gutter would just create more places for potential problems whereas double barrel lugs would accomplish the same thing as a gutter and it would be a much easier and neater job. The only issue I can think of is making the connection of the GEC to the neutral in the meter can although 250.24 permits the connection in the can there may not be a convenient spot for the connection and the other two neutrals.

However even if the AHJ would allow me to use double barrel lugs in the meter can I still would like to understand how to size a gutter properly so if anyone could help point me in the right direction I would greatly appreciate the help.

 

[augie47]

1st let me say I agree with others that a wireway is probably not the ideal solution and, there is some misunderstanding if the inspector is considering these as "parallel feeders" (a: they are not feeders and b: they are not parallel).
That said, at first look, your math is correct.
You would need to keep 312.6 in mind and the size of the polaris connector (often that has more to do with sizing than fill)