Electrical Duct Bank Sizing

[new_ee]

For an apartment building with 3 services where the disconnect and metering equipment (for each of 3 services) is located on 2nd, 3rd, and 4th floors an electrical duct bank is needed to get the service entrance conductors to their respective main disconnect (so they'll be considered running outside of the building). This will be concrete enclosed duct bank (running vertically from ground up to each floor). Once I figure out all the conductor and conduit sizes. How do I determine the separation between the ducts? Is it just 2 inches between each one? And then 2 inches to the edge? For the conductors to be considered outside of the building? Or is there more to it than that? (ANNEX B?)

EX. Lets say that there are (3) 1200 amp services (1) on each of the 2nd, 3rd, 4th floors. Each 1200 amp service will require (4) sets of 500 kcmil (alu 75 degree) conductors each set in 4in conduit. Thats a total of 12 sets of conductors (4in conduits for all three services to the building). So by my calculations a 38" by 14" duct bank (with 2 columns and 6 rows of ducts) will be needed. Is this right?

 

[new_ee]

This is 208V, 3-Phase.

 

[RUWired]

New__ee,As far duct bank spacing,..7-1/2" center to center.With 4" pvc pipe there is 3" of space between them and 3" on sides for concrete.With a 12 pack, it should be a 26 x 33 duct bank.What poco is allowing this set up?Or is this hypothetical.
Rick

 

[RUWired]

With a 2x6 duct bank....18"x48"

 

[new_ee]

This is hypothetical. When I talked to poco they said it would be ok but owner is responsible for supplying conductors and conduit from the poco's transformer (where ever it may be located). If anyone has done a larger apartment complex like this and has a better idea, I'm all ears. Also architect wants service inside and 1st floor does not have space for electrical.

 

[new_ee]

also do the conductors have to be further derated due to the duct bank?

 

[tkb]

I would have the architech design an electric room on the ground floor for a piece of switchgear.
Have the tenant breakers unmetered for feeders on each floor to be centraly metered in an electric room on each floor.
Also I would have a metered section of the gear for the owners panels that may be required on each floor.

Forget about the vertical concrete duct bank. It would most likely cost more.

 

[ramdiesel3500]

I recently did a 6-story apartment complex design-build. We set a 3000 amp 120/208V SE switch on the first floor. Then we fed vertical 3000A bus-duct (much smaller, lighter weight, and easier to install than pipe & concrete) all the way up through the building hitting an electrical closet on each floor. At each closet we had an 800A bus head that fed a meter center for tenant meters and a house meter. POCO has a key to each closet and reads all the meters every month. POCO approved this installation as well as the inspectors/AHJ!

Whats nice about the bus-way is that it only occupies about a 12" x 18" floor space as it runs vertically. There is no issue with supporting vertical runs of conductors. It just bolts together quickly and easily. The manufacturer will send a rep to measure the installation and then take responsibility for making it fit together!

Yes, it is expensive, but we found that it was actually much less expensive than pipe & wire!

 

[new_ee]

I recently did a 6-story apartment complex design-build. We set a 3000 amp 120/208V SE switch on the first floor. Then we fed vertical 3000A bus-duct (much smaller, lighter weight, and easier to install than pipe & concrete) all the way up through the building hitting an electrical closet on each floor. At each closet we had an 800A bus head that fed a meter center for tenant meters and a house meter. POCO has a key to each closet and reads all the meters every month. POCO approved this installation as well as the inspectors/AHJ!

Whats nice about the bus-way is that it only occupies about a 12" x 18" floor space as it runs vertically. There is no issue with supporting vertical runs of conductors. It just bolts together quickly and easily. The manufacturer will send a rep to measure the installation and then take responsibility for making it fit together!

Yes, it is expensive, but we found that it was actually much less expensive than pipe & wire!

I was thinking about this exact layout as an alternative. It might be too late now, but I'll keep it in mind for next time.